ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 51,2025 Issue 5
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- The Future Projections of Extreme Weather, Climate and Water Events and Strategic Responses
- A Review of Downburst Genesis Mechanism and Warning
- The Pattern Structure and Thermodynamic and Dynamic Processes of Severe Storms Associated with Linear Convective Gales
- Analysis on Extremity and Characteristics of the “21·7” Severe Torrential Rain in Henan Province
- Diagnostic Analysis on Water Vapor and Jet Characteristics of the July 2021 Severe Torrential Rain in Henan Province
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2025,51(5):517-528, DOI: 10.7519/j.issn.1000-0526.2025.033101
Abstract:
This study presents a comparative analysis of wind observations between a Doppler weather radar and a wind lidar. By integrating high-resolution vertical profiles of horizontal/vertical wind speeds and directions from the wind lidar, the radial velocities of the wind profiles relative to the Doppler weather radar are derived, and the consistency of these velocities with radial velocities from nighttime clear-air echoes observed by the weather radar is analyzed. This method was applied to evaluate the May 2023 data from the CINRAD/SA Doppler weather radar and a co-located wind lidar in Daxing, Beijing. The results indicate that there is a mean radial velocity difference of 0.37 m·s-1 between the two systems with a monthly standard deviation of 3.66 m·s-1. Daily assessments suggest that the average differences of radial velocities in 23 days between the two systems are within ±1 m·s-1, while their standard deviations in 25 days are below 4 m·s-1. The analysis demonstrates that the radial velocity of weather radar can be analyzed day by day and month by month based on wind lidar data combined with weather radar clear-air echo, supporting early detection of biases caused by equipment malfunctions or inadequate maintenance. Furthermore, the results confirm that the clear-air echo of weather radar is mainly generated by meteorological factors, and the radial velocity of clear-air echo of weather radar at night can represent the atmospheric wind field velocity. The nighttime clear-air echoes observed by the weather radar can predominantly reflect meteorological characteristics, with their radial velocities accurately representing atmospheric wind field.
This study presents a comparative analysis of wind observations between a Doppler weather radar and a wind lidar. By integrating high-resolution vertical profiles of horizontal/vertical wind speeds and directions from the wind lidar, the radial velocities of the wind profiles relative to the Doppler weather radar are derived, and the consistency of these velocities with radial velocities from nighttime clear-air echoes observed by the weather radar is analyzed. This method was applied to evaluate the May 2023 data from the CINRAD/SA Doppler weather radar and a co-located wind lidar in Daxing, Beijing. The results indicate that there is a mean radial velocity difference of 0.37 m·s-1 between the two systems with a monthly standard deviation of 3.66 m·s-1. Daily assessments suggest that the average differences of radial velocities in 23 days between the two systems are within ±1 m·s-1, while their standard deviations in 25 days are below 4 m·s-1. The analysis demonstrates that the radial velocity of weather radar can be analyzed day by day and month by month based on wind lidar data combined with weather radar clear-air echo, supporting early detection of biases caused by equipment malfunctions or inadequate maintenance. Furthermore, the results confirm that the clear-air echo of weather radar is mainly generated by meteorological factors, and the radial velocity of clear-air echo of weather radar at night can represent the atmospheric wind field velocity. The nighttime clear-air echoes observed by the weather radar can predominantly reflect meteorological characteristics, with their radial velocities accurately representing atmospheric wind field.
2025,51(5):529-541, DOI: 10.7519/j.issn.1000-0526.2025.040101
Abstract:
To evaluate the reliability of the atmospheric temperature profiles retrieved by the microwave radiometer (MWR) and the impact of sounding balloon drift on the temperature differences (δT) between MWR and radiosonde, more than two years of temperature profiles derived from MWR of Xi’an Jinghe Station in Shaanxi Province are tested against those from radiosondes. A method for quantitative assessment of bias in radiosonde temperature caused by the drift of sounding balloon is proposed. It is demonstrated that there are significant spatial and temporal changes in the consistency of the temperatures acquired by MWR (TM) and radiosonde (TS). The correlation coefficients between TM and TS are found to be higher in spring and autumn than in summer and winter, and better correlation is always detected at lower altitudes in all seasons. At a given altitude, the δT is 〖JP2〗significantly negatively correlated to the ambient temperature represented by TS. The higher the temperature, the more obvious the underestimation of the temperature by the MWR, and vice versa. This leads to a phenomenon of “overestimating low temperature and underestimating high temperature”, which is more obvious at high altitudes than at low altitudes, and more obvious in winter and summer than in spring and autumn. The drift of sounding balloon causes the sounding temperature to be higher than the actual temperature right above the radiosonde sites in all seasons, and the biases in radiosonde temperature records are negatively correlated to the ambient temperature. Therefore, sounding balloon drift causes mean deviation (MD) to be overestimated, and the degree of dispersion in δT to be underestimated, resulting in underestimation of the correlation between δT and ambient temperature as well as the severity of “overestimating low temperature and underestimating high temperature” of MWR. Overall, the influence of sounding balloon drift on the standard deviation of δT and root mean square deviation (RMSD) of the microwave radiometer and radiosonde temperature is below 2%, and its contribution to δT is much smaller than that of the retrieval algorithm.
To evaluate the reliability of the atmospheric temperature profiles retrieved by the microwave radiometer (MWR) and the impact of sounding balloon drift on the temperature differences (δT) between MWR and radiosonde, more than two years of temperature profiles derived from MWR of Xi’an Jinghe Station in Shaanxi Province are tested against those from radiosondes. A method for quantitative assessment of bias in radiosonde temperature caused by the drift of sounding balloon is proposed. It is demonstrated that there are significant spatial and temporal changes in the consistency of the temperatures acquired by MWR (TM) and radiosonde (TS). The correlation coefficients between TM and TS are found to be higher in spring and autumn than in summer and winter, and better correlation is always detected at lower altitudes in all seasons. At a given altitude, the δT is 〖JP2〗significantly negatively correlated to the ambient temperature represented by TS. The higher the temperature, the more obvious the underestimation of the temperature by the MWR, and vice versa. This leads to a phenomenon of “overestimating low temperature and underestimating high temperature”, which is more obvious at high altitudes than at low altitudes, and more obvious in winter and summer than in spring and autumn. The drift of sounding balloon causes the sounding temperature to be higher than the actual temperature right above the radiosonde sites in all seasons, and the biases in radiosonde temperature records are negatively correlated to the ambient temperature. Therefore, sounding balloon drift causes mean deviation (MD) to be overestimated, and the degree of dispersion in δT to be underestimated, resulting in underestimation of the correlation between δT and ambient temperature as well as the severity of “overestimating low temperature and underestimating high temperature” of MWR. Overall, the influence of sounding balloon drift on the standard deviation of δT and root mean square deviation (RMSD) of the microwave radiometer and radiosonde temperature is below 2%, and its contribution to δT is much smaller than that of the retrieval algorithm.
2025,51(5):542-551, DOI: 10.7519/j.issn.1000-0526.2024.111801
Abstract:
Doppler spectrum is the Ka-band cloud radar original data. Based on the consistency difference between cloud-precipitation signal and the “ghost echo” along with other noise signals in different Doppler spectral modes, this article uses the difference between short-pulse and long-pulse modes to determine the cloud signal boundary for the first time. The “ghost echo” is removed and the cloud signal boundary is adopted to calculate the noise level, forming a new denoising method. In addition, the sensitivity of cloud signal boundary changing with the difference threshold T is analyzed. Based on the small particle tracer method, the left cloud signal boundary after denoising is used to calculate the vertical air velocity. Two rainfall (snow) cases in Beijing are analyzed and compared with the in-situ aircraft observations of the vertical air velocity. It is verified that the new denoising method can effectively remove the “ghost echo”. Although a certain percentage deviation exists between the average vertical air velocity obtained by cloud radar and aircraft, the direction and magnitude correspond well in general. Thus, this method and the retrieved results are reasonable.
Doppler spectrum is the Ka-band cloud radar original data. Based on the consistency difference between cloud-precipitation signal and the “ghost echo” along with other noise signals in different Doppler spectral modes, this article uses the difference between short-pulse and long-pulse modes to determine the cloud signal boundary for the first time. The “ghost echo” is removed and the cloud signal boundary is adopted to calculate the noise level, forming a new denoising method. In addition, the sensitivity of cloud signal boundary changing with the difference threshold T is analyzed. Based on the small particle tracer method, the left cloud signal boundary after denoising is used to calculate the vertical air velocity. Two rainfall (snow) cases in Beijing are analyzed and compared with the in-situ aircraft observations of the vertical air velocity. It is verified that the new denoising method can effectively remove the “ghost echo”. Although a certain percentage deviation exists between the average vertical air velocity obtained by cloud radar and aircraft, the direction and magnitude correspond well in general. Thus, this method and the retrieved results are reasonable.
2025,51(5):552-565, DOI: 10.7519/j.issn.1000-0526.2025.021601
Abstract:
Based on the parallel observation data of GTS12 and GTS1 radiosondes from 89 high altitude meteorological observation stations in China and the CMA-GFS model field data, a comparative analysis and evaluation of the observation data of the two radiosondes on each mandatory level are conducted. The results show that the GTS12 and GTS1 radiosondes have good consistency in temperature and geopotential height observation data, and the absolute values of biases in temperature and geopotential height are less than 0.5℃ and 30.0 gpm except on a few mandatory levels. The relative humidity observed by GTS12 radio-sonde is about 4.6% higher than that by GTS1 radiosonde on average. For the stability of observation data, there is not much difference between the two types of radiosondes on the middle and lower mandatory levels. On the upper mandatory levels, the temperature and geopotential height observed by the GTS12 radio-sonde are significantly superior to those by the GTS1 radiosonde, but the relative humidity by the former is slightly worse than that by the latter. The absolute average biases of temperature observed by GTS12 and GTS1 radiosondes relative to the CMA-GFS model data are about 0.34℃ and 0.44℃, respectively. Their average root mean square errors are about 1.23℃ and 1.31℃, and the average correlation coefficients are about 0.908 and 0.916, respectively. The corresponding geopotential heights are 11.05 gpm and 14.97 gpm, 18.76 gpm and 25.16 gpm, 0.948 and 0.934 and the corresponding relative humidities are 5.26% and 8.59%, 16.19% and 18.44%, 0.687 and 0.627, which indicate that the consistency between the observation data by the GTS12 radiosonde and the CMA-GFS model data is better than that of the GTS1 radiosonde with the model. The improvement of GTS12 radiosonde sensor technology has effectively enhanced the overall observation performance of the radiosonde.
Based on the parallel observation data of GTS12 and GTS1 radiosondes from 89 high altitude meteorological observation stations in China and the CMA-GFS model field data, a comparative analysis and evaluation of the observation data of the two radiosondes on each mandatory level are conducted. The results show that the GTS12 and GTS1 radiosondes have good consistency in temperature and geopotential height observation data, and the absolute values of biases in temperature and geopotential height are less than 0.5℃ and 30.0 gpm except on a few mandatory levels. The relative humidity observed by GTS12 radio-sonde is about 4.6% higher than that by GTS1 radiosonde on average. For the stability of observation data, there is not much difference between the two types of radiosondes on the middle and lower mandatory levels. On the upper mandatory levels, the temperature and geopotential height observed by the GTS12 radio-sonde are significantly superior to those by the GTS1 radiosonde, but the relative humidity by the former is slightly worse than that by the latter. The absolute average biases of temperature observed by GTS12 and GTS1 radiosondes relative to the CMA-GFS model data are about 0.34℃ and 0.44℃, respectively. Their average root mean square errors are about 1.23℃ and 1.31℃, and the average correlation coefficients are about 0.908 and 0.916, respectively. The corresponding geopotential heights are 11.05 gpm and 14.97 gpm, 18.76 gpm and 25.16 gpm, 0.948 and 0.934 and the corresponding relative humidities are 5.26% and 8.59%, 16.19% and 18.44%, 0.687 and 0.627, which indicate that the consistency between the observation data by the GTS12 radiosonde and the CMA-GFS model data is better than that of the GTS1 radiosonde with the model. The improvement of GTS12 radiosonde sensor technology has effectively enhanced the overall observation performance of the radiosonde.
2025,51(5):566-580, DOI: 10.7519/j.issn.1000-0526.2025.011501
Abstract:
From 21 May to 21 June 2022, the heaviest dragon-boat precipitation process in the last decade occurred in South China. This extreme precipitation process, featured with strong extremity, large accumulated rainfall and frequent occurrence of severe rainfall, caused significant economic losses. In this paper, the forecast products from two operational models, TRAMS and ECMWF, which are commonly used in South China, are selected to divide the torrential rain processes during dragon-boat precipitation into front-zone torrential rain and warm-sector torrential rain. The results are verified and evaluated, so as to understand the characteristics of the two models’ biases for the front-zone torrential rain and warm-sector torrential rain under the background of the extreme dragon-boat precipitation. Compared with the traditional point-to-point method, the MODE method can effectively avoid the phenomenon of high false alarm ratio caused by precipitation position deviation in the model. Further analysis of the number, position, precipitation area and intensity of torrential rain objects based on MODE method shows that the high-resolution model TRAMS has better ability to identify and match torrential rain objects than the global model ECMWF. The location of warm-sector torrential rain predicted by TRAMS is mostly biased to the east, while the front-zone torrential rain predicted by ECMWF is basically biased to the north. The deviations in precipitation position in the above two are closely related to the forecast errors of southerly airflow at low altitude by different models. The area prediction of the front-zone torrential rain by TRAMS is close to the observation, but the forecast area of warm-sector torrential rain is larger. The forecast areas by ECMWF for both front-zone torrential rain and warm-sector torrential rain are smaller. The prediction of torrential rain intensity and extreme value by TRAMS is closer to the observation than that by ECMWF, but it still underestimates the extreme precipitation. This study can provide new experience for forecasters to understand the prediction biases of different operational models for dragon-boat precipitation process. It also has some reference values for model developers to further carry out research on error source diagnosis and technical improvement of TRAMS model.
From 21 May to 21 June 2022, the heaviest dragon-boat precipitation process in the last decade occurred in South China. This extreme precipitation process, featured with strong extremity, large accumulated rainfall and frequent occurrence of severe rainfall, caused significant economic losses. In this paper, the forecast products from two operational models, TRAMS and ECMWF, which are commonly used in South China, are selected to divide the torrential rain processes during dragon-boat precipitation into front-zone torrential rain and warm-sector torrential rain. The results are verified and evaluated, so as to understand the characteristics of the two models’ biases for the front-zone torrential rain and warm-sector torrential rain under the background of the extreme dragon-boat precipitation. Compared with the traditional point-to-point method, the MODE method can effectively avoid the phenomenon of high false alarm ratio caused by precipitation position deviation in the model. Further analysis of the number, position, precipitation area and intensity of torrential rain objects based on MODE method shows that the high-resolution model TRAMS has better ability to identify and match torrential rain objects than the global model ECMWF. The location of warm-sector torrential rain predicted by TRAMS is mostly biased to the east, while the front-zone torrential rain predicted by ECMWF is basically biased to the north. The deviations in precipitation position in the above two are closely related to the forecast errors of southerly airflow at low altitude by different models. The area prediction of the front-zone torrential rain by TRAMS is close to the observation, but the forecast area of warm-sector torrential rain is larger. The forecast areas by ECMWF for both front-zone torrential rain and warm-sector torrential rain are smaller. The prediction of torrential rain intensity and extreme value by TRAMS is closer to the observation than that by ECMWF, but it still underestimates the extreme precipitation. This study can provide new experience for forecasters to understand the prediction biases of different operational models for dragon-boat precipitation process. It also has some reference values for model developers to further carry out research on error source diagnosis and technical improvement of TRAMS model.
2025,51(5):581-594, DOI: 10.7519/j.issn.1000-0526.2025.010202
Abstract:
The refined precipitation forecasts from numerical prediction models are of a crucial support to flood control efforts within river basins. The continuous heavy rainfall during the Meiyu season in 2020 led to the heaviest flood event since the construction of the Xin’anjiang Reservoir and it was the first time that all the sluices were fully opened. Based on precipitation observation data from various stations, this paper examines the forecast performance of four global models and four regional models regarding both overall precipitation patterns and areal rainfall within Xin’anjiang Basin. Additionally, it focuses on evaluating the predictive capabilities of these models regarding extreme and cumulative precipitation effects in the basin to understand whether they can meet the demand of reservoir flood discharge forecasting service. Furthermore, an analysis is conducted to assess how terrain height influences models’ precipitation forecasts. The results show that the global models consistently underestimate the precipitation and have weaker prediction ability for extreme precipitation than the regional models. The regional models mostly overestimate the precipitation but have relatively large variations among the predictions. The regional multi-model ensemble average demonstrates a better forecast performance than single-model results. The regional models perform well in forecasting rainfall of rainstorm to heavy rainstorm, but have some discrepancies in predicting the locations and timing of heavy rainstorm. Compare to the model evaluation of single-day precipitation forecast, it is more instructive to comprehensively consider the cumulative effects and extremity of precipitation prediction. Terrain height significantly influences the prediction of rainstorm events and above. As the terrain height increases, the advantage of regional models becomes evident while the predictive ability of global models for rainstorm events decreases. Especially for ZJWARMS and ZJWARRS, the TS scores increase from below 0.10 to approximately 0.15 or so. Additionally, moderate or lighter intensity rains are not affected by terrain so obviously.
The refined precipitation forecasts from numerical prediction models are of a crucial support to flood control efforts within river basins. The continuous heavy rainfall during the Meiyu season in 2020 led to the heaviest flood event since the construction of the Xin’anjiang Reservoir and it was the first time that all the sluices were fully opened. Based on precipitation observation data from various stations, this paper examines the forecast performance of four global models and four regional models regarding both overall precipitation patterns and areal rainfall within Xin’anjiang Basin. Additionally, it focuses on evaluating the predictive capabilities of these models regarding extreme and cumulative precipitation effects in the basin to understand whether they can meet the demand of reservoir flood discharge forecasting service. Furthermore, an analysis is conducted to assess how terrain height influences models’ precipitation forecasts. The results show that the global models consistently underestimate the precipitation and have weaker prediction ability for extreme precipitation than the regional models. The regional models mostly overestimate the precipitation but have relatively large variations among the predictions. The regional multi-model ensemble average demonstrates a better forecast performance than single-model results. The regional models perform well in forecasting rainfall of rainstorm to heavy rainstorm, but have some discrepancies in predicting the locations and timing of heavy rainstorm. Compare to the model evaluation of single-day precipitation forecast, it is more instructive to comprehensively consider the cumulative effects and extremity of precipitation prediction. Terrain height significantly influences the prediction of rainstorm events and above. As the terrain height increases, the advantage of regional models becomes evident while the predictive ability of global models for rainstorm events decreases. Especially for ZJWARMS and ZJWARRS, the TS scores increase from below 0.10 to approximately 0.15 or so. Additionally, moderate or lighter intensity rains are not affected by terrain so obviously.
2025,51(5):595-606, DOI: 10.7519/j.issn.1000-0526.2024.122703
Abstract:
Based on the observation data by Guyuan C-band Doppler weather radar and X-band dual polarization radar, combined with ERA5 hourly reanalysis data, Himawari-8 satellite images and conventional observation data, we analyze the causes and radar observation characteristics of a local outsize hail (diameter ≥ 5 cm) which occurred in Liupan Moutains of Ningxia on 12 July 2021. The results show that the supercell storm formed by the merger and development of multicell storm led to the occurrence of outsize hail. The mesoscale surface convergence line, mesoscale cyclone and local circulation in Liupan Moutains were the main triggering and enhancing systems of mesoscale convective system (MCS), and also affected the moving direction of MCS. When the large hail occurred, the C-band radar reflectivity factor (Z) ≥ 65 dBz, three-body scatter spike (TBSS) length ≥ 20 km, and vertically integrated liquid water content (VIL) ≥ 40 kg·m-2. The correlation coefficient (CC) in the high-value zone of the low layer horizontal reflectivity (ZH) of X-band radar was less than 0.8, and the differential reflectivity (ZDR) and specific differential phase (KDP) of the mid- and high-layers ZH high-value zone were negative with CC＜ 0.8. When the outsize hail occurred, Z ≥ 70 dBz, TBSS length ≥ 30 km and VIL ≥ 50 kg·m-2 for the C-band radar. CC in the low layer ZH high-value zone of the X-band radar was less than 0.6, and the “hole” formed in the area with CC＜ 0.5, was useful to identify the area and altitude of outsize hail in the air. ZDR columns and CC rings near the bounded weak echo zone could indicate the position of strong updrafts in the middle and upper layers of supercell storm. So, ZH and dual polarization parameter characteristics have good indicative significance for the identification and warning of hails in different sizes.
Based on the observation data by Guyuan C-band Doppler weather radar and X-band dual polarization radar, combined with ERA5 hourly reanalysis data, Himawari-8 satellite images and conventional observation data, we analyze the causes and radar observation characteristics of a local outsize hail (diameter ≥ 5 cm) which occurred in Liupan Moutains of Ningxia on 12 July 2021. The results show that the supercell storm formed by the merger and development of multicell storm led to the occurrence of outsize hail. The mesoscale surface convergence line, mesoscale cyclone and local circulation in Liupan Moutains were the main triggering and enhancing systems of mesoscale convective system (MCS), and also affected the moving direction of MCS. When the large hail occurred, the C-band radar reflectivity factor (Z) ≥ 65 dBz, three-body scatter spike (TBSS) length ≥ 20 km, and vertically integrated liquid water content (VIL) ≥ 40 kg·m-2. The correlation coefficient (CC) in the high-value zone of the low layer horizontal reflectivity (ZH) of X-band radar was less than 0.8, and the differential reflectivity (ZDR) and specific differential phase (KDP) of the mid- and high-layers ZH high-value zone were negative with CC＜ 0.8. When the outsize hail occurred, Z ≥ 70 dBz, TBSS length ≥ 30 km and VIL ≥ 50 kg·m-2 for the C-band radar. CC in the low layer ZH high-value zone of the X-band radar was less than 0.6, and the “hole” formed in the area with CC＜ 0.5, was useful to identify the area and altitude of outsize hail in the air. ZDR columns and CC rings near the bounded weak echo zone could indicate the position of strong updrafts in the middle and upper layers of supercell storm. So, ZH and dual polarization parameter characteristics have good indicative significance for the identification and warning of hails in different sizes.
2025,51(5):607-617, DOI: 10.7519/j.issn.1000-0526.2025.031901
Abstract:
The boundary layer low-level jet can enhance the exchange of matter and energy, and is closely related to precipitation, air pollution and other issues. Studying the boundary layer low-level jet helps to improve the forecasting ability of air pollution and extreme weather. During the study of the boundary layer low-level jet in Beijing by using the Doppler wind lidar data from March 2018 to February 2019, a special jet was found. By using the numerical simulation method, this paper analyzes the formation mechanism of this phenomenon. The results are as follows. The jet intensity is about 6 m·s-1, appearing mainly from 02:00 BT to 09:00 BT. The thickness of the jet is only about 500 m, and the height of the jet axis is only 200-300 m, which is obviously lower than that of the classical boundary layer low-level jet. The vertical wind shear is obvious. The dominant wind inside the jet is northeast wind, while above the jet is southwest wind. In the wind direction conversion area, a weak wind speed zone is formed, wrapping the low-level jet, so it is called the weak wind speed zone boundary layer low-level jet (WBLLJ). Terrain forcing is the root cause for the formation of WBLLJ. Blocked by Taihang Mountains and Yanshan Mountains, under the joint action of night topographic cold discharge, a shallow northeast wind control zone, which is 130 km long, 10 km wide, and 600 m high， is formed in the plain area near the mountain. This wind zone is the location of the WBLLJ, and can also explain the cause of the low-level jet height. A large amount of cold air brought by the mountain wind at night wedges into the bottom of the plain and forms obvious topographic inversion. Under the action of the inversion layer, the atmospheric turbulent motion weakens rapidly, and the upper air flow is decoupled from the ground forming a low-level jet. With the thickening and southward expansion of the plain cold pool, the low-level jet continues to develop southward and upward. The low-level jet gradually weakens and dissipates with the dissipation of the inversion layer after sunrise. The WBLLJ plays an important role in the diffusion of atmospheric bottom-layer pollutants and the evolution of urban heat island in Beijing.
The boundary layer low-level jet can enhance the exchange of matter and energy, and is closely related to precipitation, air pollution and other issues. Studying the boundary layer low-level jet helps to improve the forecasting ability of air pollution and extreme weather. During the study of the boundary layer low-level jet in Beijing by using the Doppler wind lidar data from March 2018 to February 2019, a special jet was found. By using the numerical simulation method, this paper analyzes the formation mechanism of this phenomenon. The results are as follows. The jet intensity is about 6 m·s-1, appearing mainly from 02:00 BT to 09:00 BT. The thickness of the jet is only about 500 m, and the height of the jet axis is only 200-300 m, which is obviously lower than that of the classical boundary layer low-level jet. The vertical wind shear is obvious. The dominant wind inside the jet is northeast wind, while above the jet is southwest wind. In the wind direction conversion area, a weak wind speed zone is formed, wrapping the low-level jet, so it is called the weak wind speed zone boundary layer low-level jet (WBLLJ). Terrain forcing is the root cause for the formation of WBLLJ. Blocked by Taihang Mountains and Yanshan Mountains, under the joint action of night topographic cold discharge, a shallow northeast wind control zone, which is 130 km long, 10 km wide, and 600 m high， is formed in the plain area near the mountain. This wind zone is the location of the WBLLJ, and can also explain the cause of the low-level jet height. A large amount of cold air brought by the mountain wind at night wedges into the bottom of the plain and forms obvious topographic inversion. Under the action of the inversion layer, the atmospheric turbulent motion weakens rapidly, and the upper air flow is decoupled from the ground forming a low-level jet. With the thickening and southward expansion of the plain cold pool, the low-level jet continues to develop southward and upward. The low-level jet gradually weakens and dissipates with the dissipation of the inversion layer after sunrise. The WBLLJ plays an important role in the diffusion of atmospheric bottom-layer pollutants and the evolution of urban heat island in Beijing.
2025,51(5):618-627, DOI: 10.7519/j.issn.1000-0526.2024.121701
Abstract:
The three consecutive La Nina events that occurred from 2020 to 2023 have been widespread concerned, and they also led to various global weather and climate anomalies. By statistically analyzing the tropical cyclone datasets from the National Meteorological Centre of China Meteorological Administration and the National Hurricane Center of the United States, we find that the number of tropical cyclones generated in the North Pacific in September 2022 was far more than the historical average over the same period, with the number of tropical cyclones in the Northeast Pacific reaching a new high in the past 70 years. Based on the reanalysis data and the analysis of the dynamic genesis potential index, it is found that the vertical motion in the middle troposphere made a great contribution to the increased number of tropical cyclones in the North Pacific. Further analysis suggests that during the La Nina events, the temperature of warm pool in the Northwest Pacific continued to rise, convective activity near the Philippines enhanced and the southwesterlies over maritime continent strengthened, which forced the subtropical high over the Northwest Pacific to shift northward. The emergence of low-level cyclonic circulation developing from the anticyclonic circulation in the active tropical cyclone area of the Northwest Pacific enhanced the ascending motion of the middle troposphere, which was favorable for the genesis of tropical cyclones. At the same time, the La Nina events led to continuous increase in the meridional temperature gradient over the Northeast Pacific and the meridional Hadley cell got intensified, so the upward movement over the middle and low latitudes strengthened. As the subtropical high located in western Mexico moved eastward, the number of active tropical cyclones in the Northeast Pacific increased.
The three consecutive La Nina events that occurred from 2020 to 2023 have been widespread concerned, and they also led to various global weather and climate anomalies. By statistically analyzing the tropical cyclone datasets from the National Meteorological Centre of China Meteorological Administration and the National Hurricane Center of the United States, we find that the number of tropical cyclones generated in the North Pacific in September 2022 was far more than the historical average over the same period, with the number of tropical cyclones in the Northeast Pacific reaching a new high in the past 70 years. Based on the reanalysis data and the analysis of the dynamic genesis potential index, it is found that the vertical motion in the middle troposphere made a great contribution to the increased number of tropical cyclones in the North Pacific. Further analysis suggests that during the La Nina events, the temperature of warm pool in the Northwest Pacific continued to rise, convective activity near the Philippines enhanced and the southwesterlies over maritime continent strengthened, which forced the subtropical high over the Northwest Pacific to shift northward. The emergence of low-level cyclonic circulation developing from the anticyclonic circulation in the active tropical cyclone area of the Northwest Pacific enhanced the ascending motion of the middle troposphere, which was favorable for the genesis of tropical cyclones. At the same time, the La Nina events led to continuous increase in the meridional temperature gradient over the Northeast Pacific and the meridional Hadley cell got intensified, so the upward movement over the middle and low latitudes strengthened. As the subtropical high located in western Mexico moved eastward, the number of active tropical cyclones in the Northeast Pacific increased.
QIAO Qi, LI Ying, YANG Guowei, CHEN Yixiao, HONG Haixu, DAI Tanlong, ZHU Xiaojin, WANG Youmin, WANG Guofu
2025,51(5):628-635, DOI: 10.7519/j.issn.1000-0526.2025.031601
Abstract:
In 2024, the global mean surface air temperature was 1.49℃ above the pre-industrial average, and 0.61℃ higher than the average value from 1991 to 2020, making 2024 become the hottest year in global meteorological records. Both the global sea surface temperature and the ocean heat content above 2000 m height reached unprecedented highs in records. Antarctic and Arctic sea ice extents in 2024 were both clearly below the average. Kazakhstan, Pakistan, Afghanistan, Republic of Korea, France, Russia, Indonesia, South Africa, China, and other places experienced extremely severe rainfall, floods, landslides and other secondary disasters. Northern India and many parts of Europe suffered high temperatures and heat waves. Brazil was caught by the heaviest drought in records. The losses caused by tropical cyclones were serious, and multiple tornados occurred in the United States.
In 2024, the global mean surface air temperature was 1.49℃ above the pre-industrial average, and 0.61℃ higher than the average value from 1991 to 2020, making 2024 become the hottest year in global meteorological records. Both the global sea surface temperature and the ocean heat content above 2000 m height reached unprecedented highs in records. Antarctic and Arctic sea ice extents in 2024 were both clearly below the average. Kazakhstan, Pakistan, Afghanistan, Republic of Korea, France, Russia, Indonesia, South Africa, China, and other places experienced extremely severe rainfall, floods, landslides and other secondary disasters. Northern India and many parts of Europe suffered high temperatures and heat waves. Brazil was caught by the heaviest drought in records. The losses caused by tropical cyclones were serious, and multiple tornados occurred in the United States.
2025,51(5):636-644, DOI: 10.7519/j.issn.1000-0526.2025.042901
Abstract:
The main characteristics of the atmospheric circulation in the Northern Hemisphere in February 2025 are as follows. The polar vortex was distributed in a dipole-shaped pattern. The polar vortex in the Eastern Hemisphere, located over the central Siberian Plateau to the Sea of Okhotsk, was weaker than normal, and a low vortex which was split from the polar vortex controlled the mid-latitude northwestern Pacific Region. The average trough above the eastern part of East Asia was stronger than usual, and the southern branch trough was more eastward and active. The national mean temperature in February was 0.4℃ lower than in the same period of previous years, while the mean temperatures in southern part of Northeast China, central Inner Mongolia, northern part of North China, western Guizhou Province and western Guangxi Province were 2-4℃ lower than usual. The national average precipitation was about 35% less than normal. The precipitation in Xinjiang, west-central Inner Mongolia, North China, the west-central part of the Huanghuai Region, the Jianghuai Region, and the east-central part of South China was more than 80% less than usual. However, most parts of Southwest China and the east-central part of Northwest China received precipitation more than doubled. During this month, cold air activities occurred frequently and there were two strong cold air processes and one cold wave event, among which the cold wave from 6 to 8 February caused a sharp drop in temperature and significant low temperature. The southern branch trough guided the warm-moist air from low latitudes to flow into southern China, where it joined the southward-moving cold air, leading to five large-scale rain and snow events. Overall, the key challenge in forecasting lies in how to timely use multi-source observational real-time data within medium- and short-term lead time period to conduct forecast verification, adjust intensity and movement paths of high- and low-level systems, and improve the accuracy of temperature drop and precipitation forecasts.
The main characteristics of the atmospheric circulation in the Northern Hemisphere in February 2025 are as follows. The polar vortex was distributed in a dipole-shaped pattern. The polar vortex in the Eastern Hemisphere, located over the central Siberian Plateau to the Sea of Okhotsk, was weaker than normal, and a low vortex which was split from the polar vortex controlled the mid-latitude northwestern Pacific Region. The average trough above the eastern part of East Asia was stronger than usual, and the southern branch trough was more eastward and active. The national mean temperature in February was 0.4℃ lower than in the same period of previous years, while the mean temperatures in southern part of Northeast China, central Inner Mongolia, northern part of North China, western Guizhou Province and western Guangxi Province were 2-4℃ lower than usual. The national average precipitation was about 35% less than normal. The precipitation in Xinjiang, west-central Inner Mongolia, North China, the west-central part of the Huanghuai Region, the Jianghuai Region, and the east-central part of South China was more than 80% less than usual. However, most parts of Southwest China and the east-central part of Northwest China received precipitation more than doubled. During this month, cold air activities occurred frequently and there were two strong cold air processes and one cold wave event, among which the cold wave from 6 to 8 February caused a sharp drop in temperature and significant low temperature. The southern branch trough guided the warm-moist air from low latitudes to flow into southern China, where it joined the southward-moving cold air, leading to five large-scale rain and snow events. Overall, the key challenge in forecasting lies in how to timely use multi-source observational real-time data within medium- and short-term lead time period to conduct forecast verification, adjust intensity and movement paths of high- and low-level systems, and improve the accuracy of temperature drop and precipitation forecasts.
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Available online: May 28, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.040401
Abstract:
Due to the limitations of the limited area, lateral boundary perturbations are one of the primary perturbation methods for regional ensemble prediction. However, it remains unclear how to construct lateral boundary perturbations for the high-resolution regional ensemble prediction system of the China Meteorological Administration (CMA) to improve forecast skill. This paper develops a mixed lateral boundary perturbation method using the perturbation field of the CMA global ensemble prediction and lateral boundary field of the regional deterministic model, and adjusts the perturbation magnitude through dynamic perturbation coefficients. The results showed that the absence of lateral boundary perturbations suppresses the growth of perturbation energy at later forecast ranges, leading to insufficient ensemble spreads. The mixed lateral boundary perturbation scheme can enhance the perturbation energy spectra at meso-α and large scales, as well as improve the spread-skill relationships and probabilistic forecast skills for isobaric element and precipitation. Compared to the mixed lateral boundary perturbation scheme, the dynamic mixed lateral boundary perturbation scheme can enhance the spectral energy above 100 km, improve the spread-skill relationships, as well as the probabilistic forecast skills for low-level variables and precipitation beyond 24 hours, exhibiting good potential for operational application.
Due to the limitations of the limited area, lateral boundary perturbations are one of the primary perturbation methods for regional ensemble prediction. However, it remains unclear how to construct lateral boundary perturbations for the high-resolution regional ensemble prediction system of the China Meteorological Administration (CMA) to improve forecast skill. This paper develops a mixed lateral boundary perturbation method using the perturbation field of the CMA global ensemble prediction and lateral boundary field of the regional deterministic model, and adjusts the perturbation magnitude through dynamic perturbation coefficients. The results showed that the absence of lateral boundary perturbations suppresses the growth of perturbation energy at later forecast ranges, leading to insufficient ensemble spreads. The mixed lateral boundary perturbation scheme can enhance the perturbation energy spectra at meso-α and large scales, as well as improve the spread-skill relationships and probabilistic forecast skills for isobaric element and precipitation. Compared to the mixed lateral boundary perturbation scheme, the dynamic mixed lateral boundary perturbation scheme can enhance the spectral energy above 100 km, improve the spread-skill relationships, as well as the probabilistic forecast skills for low-level variables and precipitation beyond 24 hours, exhibiting good potential for operational application.
Available online: May 14, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.041602
Abstract:
Based on data from automatic weather stations, buoy observation stations, and ERA5 reanalysis spanning from 2015 to 2023, this study analyzes the characteristics of sea fog at Yangshan Port. Classification decision tree models were trained and validated using a comprehensive case database of sea fog events, and compared and verified their forcast results with those of the EC model. The results indicate that 2016 recorded the highest number of foggy days, with spring and early summer being the peak season, followed by winter. During dense fog events, the dominant wind directions ranged from northeast to north and southeast. Southeast winds prevailed during non-precipitation periods, while north winds dominated during precipitation. Monthly wind patterns transitioned from predominantly northerly in winter to northeasterly and southeasterly in spring. In the development stage of sea fog, southeast winds were dominant; during the mature stage, northeast winds prevailed; and during dissipation, north winds dominated. Fog events accompanied by precipitation were more frequent and longer-lasting. The classification decision tree models identified the temperature-dewpoint spread as a key factor in the formation of various sea fog types. Decision tree models demonstrated a lower miss rate and higher prediction performance than the EC model, particularly in forecasting the formation and duration of advection fog, while providing valuable insights into frontal and radiation fog events.
Based on data from automatic weather stations, buoy observation stations, and ERA5 reanalysis spanning from 2015 to 2023, this study analyzes the characteristics of sea fog at Yangshan Port. Classification decision tree models were trained and validated using a comprehensive case database of sea fog events, and compared and verified their forcast results with those of the EC model. The results indicate that 2016 recorded the highest number of foggy days, with spring and early summer being the peak season, followed by winter. During dense fog events, the dominant wind directions ranged from northeast to north and southeast. Southeast winds prevailed during non-precipitation periods, while north winds dominated during precipitation. Monthly wind patterns transitioned from predominantly northerly in winter to northeasterly and southeasterly in spring. In the development stage of sea fog, southeast winds were dominant; during the mature stage, northeast winds prevailed; and during dissipation, north winds dominated. Fog events accompanied by precipitation were more frequent and longer-lasting. The classification decision tree models identified the temperature-dewpoint spread as a key factor in the formation of various sea fog types. Decision tree models demonstrated a lower miss rate and higher prediction performance than the EC model, particularly in forecasting the formation and duration of advection fog, while providing valuable insights into frontal and radiation fog events.
Available online: May 14, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.031002
Abstract:
A localized severe convective rainfall event over eastern Sichuan basin under the background of southwest vortex on 8 August 2021 was analyzed by using the Chongqing S-band dual-pol radar, ERA5 reanalysis data and CMPAS multi-source precipitation product. The results are as follow: At the early development of convection, radar observed some relative weak convective characteristics. Snow particles play a major role in ice-phase particles at middle-upper level. The proportion of drizzle identification ranges from 20% to 40%, raindrops’ size and surface rain rate are both small. During the rapid intensification, radar measurements increased rapidly as well. ZDR and KDP columns can extend well above 8 km. Uplifted droplet generates supercooled water which facilitate ice-phase process over the melting layer. Melting of descending ice hydrometeors lead to the enhancement of liquid particles’ size and concentration at low level, which intensified the surface rain rate. Convective cells were merged with each other and shift eastward subsequently. As the system weakened, dry and wet snow particles become the main component of ice-phase at middle-upper level again. Both size and number of liquid particles at middle-lower level are decreased and surface rainrate gets weakened accordingly. Dual-pol variables and hydrometeor identification can basically exhibit the characteristic of hydrometeor transformation within the convective systems and cohere reasonably with the variation of surface rain rate.
A localized severe convective rainfall event over eastern Sichuan basin under the background of southwest vortex on 8 August 2021 was analyzed by using the Chongqing S-band dual-pol radar, ERA5 reanalysis data and CMPAS multi-source precipitation product. The results are as follow: At the early development of convection, radar observed some relative weak convective characteristics. Snow particles play a major role in ice-phase particles at middle-upper level. The proportion of drizzle identification ranges from 20% to 40%, raindrops’ size and surface rain rate are both small. During the rapid intensification, radar measurements increased rapidly as well. ZDR and KDP columns can extend well above 8 km. Uplifted droplet generates supercooled water which facilitate ice-phase process over the melting layer. Melting of descending ice hydrometeors lead to the enhancement of liquid particles’ size and concentration at low level, which intensified the surface rain rate. Convective cells were merged with each other and shift eastward subsequently. As the system weakened, dry and wet snow particles become the main component of ice-phase at middle-upper level again. Both size and number of liquid particles at middle-lower level are decreased and surface rainrate gets weakened accordingly. Dual-pol variables and hydrometeor identification can basically exhibit the characteristic of hydrometeor transformation within the convective systems and cohere reasonably with the variation of surface rain rate.
Available online: May 08, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.022101
Abstract:
On December 28, 2022, multiple vehicle collisions occurred at the Zhengzhou-Xinxiang Yellow River Bridge due to heavy fog. Using ERA5 reanalysis and ground observation data, the "Anomaly-based synoptic analysis" was used to diagnose and analyze the heavy fog episode. It was found that: (1) the heavy fog weather has the characteristics of strong local suddenness, low visibility, and significant nighttime cooling; The low visibility caused by heavy fog, as well as the ice and slippery bridge deck caused by high humidity and low temperature, are the meteorological reasons for rear end vehicle accidents. (2) The weather situation is stable, with weak cold air at the bottom and warm ridges in the southwest transporting warm and humid airflow in the foggy area, and the circulation pattern is favorable for the generation of fog. (3) The water vapor flux near the Bridge is high, with weak water vapor convergence and a shallow inversion layer. The radiation cooling effect is strong, providing favorable thermal, dynamic, and stratification conditions for the occurrence and persistence of radiation fog. (4) The disturbance signals of meteorological elements can better reflect the predictable signals of heavy fog compared to signals based on the entire field. The comprehensive analysis of multiple disturbance factors can determine the dissipation time of fog.
On December 28, 2022, multiple vehicle collisions occurred at the Zhengzhou-Xinxiang Yellow River Bridge due to heavy fog. Using ERA5 reanalysis and ground observation data, the "Anomaly-based synoptic analysis" was used to diagnose and analyze the heavy fog episode. It was found that: (1) the heavy fog weather has the characteristics of strong local suddenness, low visibility, and significant nighttime cooling; The low visibility caused by heavy fog, as well as the ice and slippery bridge deck caused by high humidity and low temperature, are the meteorological reasons for rear end vehicle accidents. (2) The weather situation is stable, with weak cold air at the bottom and warm ridges in the southwest transporting warm and humid airflow in the foggy area, and the circulation pattern is favorable for the generation of fog. (3) The water vapor flux near the Bridge is high, with weak water vapor convergence and a shallow inversion layer. The radiation cooling effect is strong, providing favorable thermal, dynamic, and stratification conditions for the occurrence and persistence of radiation fog. (4) The disturbance signals of meteorological elements can better reflect the predictable signals of heavy fog compared to signals based on the entire field. The comprehensive analysis of multiple disturbance factors can determine the dissipation time of fog.
Available online: May 06, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.041802
Abstract:
Based on the China Meteorological Administration (CMA) convection-permitting ensemble prediction system (CMA-CPEPS) and regional ensemble prediction system (CMA-REPS), the precipitation forecasting performance during the 2023 flood season (from 15 June to 28 August) in China, and a case analysis of July 2023 severe torrential rain in North China was objectively and comprehensively evaluated. The results indicate that CMA-REPS has an issue with systematically overestimating precipitation forecasts, CMA-CPEPS has significantly improved this problem. Compared to CMA-REPS, CMA-CPEPS shows significantly superiority in predictive capacity for weather changes and its temporal changes, with better probability forecasting and resolution ability of precipitation. Both CMA-CPEPS and CMA-REPS exhibit low spread values, while spread/RMSE value and the spatial correlation between spread and RMSE of CMA-CPEPS and CMA-REPS are equivalent. In the July 2023 severe torrential rain in North China, CMA-CPEPS has better ability to capture precipitation details compared to CMA-REPS. CMA-CPEPS outperforms in forecasting precipitation intensity, the evolution trend of precipitation intensity, and spatio-temporal resolution of heavy precipitation, especially in short-duration heavy precipitation events. Overall, CMA-CPEPS represents a significantly enhancement over CMA-REPS in precipitation forecasting for the 2023 flood season in China.
Based on the China Meteorological Administration (CMA) convection-permitting ensemble prediction system (CMA-CPEPS) and regional ensemble prediction system (CMA-REPS), the precipitation forecasting performance during the 2023 flood season (from 15 June to 28 August) in China, and a case analysis of July 2023 severe torrential rain in North China was objectively and comprehensively evaluated. The results indicate that CMA-REPS has an issue with systematically overestimating precipitation forecasts, CMA-CPEPS has significantly improved this problem. Compared to CMA-REPS, CMA-CPEPS shows significantly superiority in predictive capacity for weather changes and its temporal changes, with better probability forecasting and resolution ability of precipitation. Both CMA-CPEPS and CMA-REPS exhibit low spread values, while spread/RMSE value and the spatial correlation between spread and RMSE of CMA-CPEPS and CMA-REPS are equivalent. In the July 2023 severe torrential rain in North China, CMA-CPEPS has better ability to capture precipitation details compared to CMA-REPS. CMA-CPEPS outperforms in forecasting precipitation intensity, the evolution trend of precipitation intensity, and spatio-temporal resolution of heavy precipitation, especially in short-duration heavy precipitation events. Overall, CMA-CPEPS represents a significantly enhancement over CMA-REPS in precipitation forecasting for the 2023 flood season in China.
Available online: April 28, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.040601
Abstract:
Abstract: Abstract: Based on observation data and ballistic theory, a simple model was established to analyze the influence of atmospheric vertical structure on the weather modification rocket ballistic performance during the ascending phase. The results indicate that the intensity and direction of the horizontal wind field have significant impact on ballistic performance, especially in low level wind fields below 1000m height. The impact of air density was relatively small. The model could be beneficial for ballistic correction, include ballistic height, deflection, and distance. It would provide relatively accurate prediction trajectory of weather modification rocket.
Abstract: Abstract: Based on observation data and ballistic theory, a simple model was established to analyze the influence of atmospheric vertical structure on the weather modification rocket ballistic performance during the ascending phase. The results indicate that the intensity and direction of the horizontal wind field have significant impact on ballistic performance, especially in low level wind fields below 1000m height. The impact of air density was relatively small. The model could be beneficial for ballistic correction, include ballistic height, deflection, and distance. It would provide relatively accurate prediction trajectory of weather modification rocket.
Available online: April 23, 2025 , DOI: 10.7519/j.issn.1000-0526.2024.123102
Abstract:
Constructing a quantitative index to characterize the intensity of low-temperature freezing injury on winter wheat and revealing its spatial-temporal variation characteristics is crucial for scientific prevention of low-temperature freezing injury of winter wheat. Based on daily meteorological observation data of winter in Jiangsu Province from 1972 to 2022, disaster data of freezing injury on winter wheat from 2010 to 2022, and yield data of historical extreme freezing injury years, the impact weights of causing factors on different types of freezing injury were determined, and three main types of freezing injury indices were established: low-temperature freezing injury(November to March), freezing injury during overwintering period(Late December to mid February), and freezing injury during regreening-jointing period(Late February to March). Multiple mathematical statistical methods such as Mann-Kendall mutation test and k-means clustering were used to conduct spatial-temporal analysis and evaluation of low-temperature freezing injury on winter wheat. Based on the ranking of freezing injury intensity during overwintering period and regreening-jointing period, two types of freezing injury are classified into three levels respectively: mild, moderate and severe. The results show that there is a significant difference in the intensity index of low-temperature freezing injury between the north and south of Jiangsu Province, which can be divided into high-risk zones (Xuzhou, Lianyungang, Suqian, Huaian, Yancheng), medium-risk zones (Nanjing, Yangzhou, Taizhou, Nantong), and low-risk zones (Zhenjiang, Changzhou, Suzhou, Wuxi). Over the past 51 years, the intensity index of low-temperature freezing injury on winter wheat experienced a sudden decline in 1989 in Jiangsu Province. The severe freezing injury during overwintering period and regreening-jointing period both jumped from a relatively multi period to a relatively low period in the late 1980s. Although the frequency of freezing injury during the growth period of winter wheat shows a decreasing trend, the intensity of extreme freezing injury is increasing, and even the freezing injury index in some areas exceeded the historical record of 1977 in the 21st century.
Constructing a quantitative index to characterize the intensity of low-temperature freezing injury on winter wheat and revealing its spatial-temporal variation characteristics is crucial for scientific prevention of low-temperature freezing injury of winter wheat. Based on daily meteorological observation data of winter in Jiangsu Province from 1972 to 2022, disaster data of freezing injury on winter wheat from 2010 to 2022, and yield data of historical extreme freezing injury years, the impact weights of causing factors on different types of freezing injury were determined, and three main types of freezing injury indices were established: low-temperature freezing injury(November to March), freezing injury during overwintering period(Late December to mid February), and freezing injury during regreening-jointing period(Late February to March). Multiple mathematical statistical methods such as Mann-Kendall mutation test and k-means clustering were used to conduct spatial-temporal analysis and evaluation of low-temperature freezing injury on winter wheat. Based on the ranking of freezing injury intensity during overwintering period and regreening-jointing period, two types of freezing injury are classified into three levels respectively: mild, moderate and severe. The results show that there is a significant difference in the intensity index of low-temperature freezing injury between the north and south of Jiangsu Province, which can be divided into high-risk zones (Xuzhou, Lianyungang, Suqian, Huaian, Yancheng), medium-risk zones (Nanjing, Yangzhou, Taizhou, Nantong), and low-risk zones (Zhenjiang, Changzhou, Suzhou, Wuxi). Over the past 51 years, the intensity index of low-temperature freezing injury on winter wheat experienced a sudden decline in 1989 in Jiangsu Province. The severe freezing injury during overwintering period and regreening-jointing period both jumped from a relatively multi period to a relatively low period in the late 1980s. Although the frequency of freezing injury during the growth period of winter wheat shows a decreasing trend, the intensity of extreme freezing injury is increasing, and even the freezing injury index in some areas exceeded the historical record of 1977 in the 21st century.
Available online: April 18, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.041801
Abstract:
The study of drought in the water source and receiving areas of the middle route project of South-to-North Water Diversion Project is of great significance for the water resource scheduling and operation management of the project. Based on the NCEP-NCAR reanalysis data and the daily average temperature, precipitation, and meteorological drought composite index of all meteorological stations in the water source and receiving areas of middle route project of South to North Water Diversion Project from 1961 to 2023, this article conducts identification and evaluation of regional drought processes in water source area and water receiving area. The results show that the annual values of drought days in the water source area and water receiving area are 101 days and 114 days, respectively, showing an overall spatial distribution characteristic of "more in the middle and less at both ends". The northern part of Henan and the southern part of Hebei in the water receiving area are high-value areas for drought days. The number of drought days in most of the water source areas, most of the water receiving areas in Henan, and eastern Hebei is increasing, while the number of drought days in most of the water receiving areas in northern, western, and southern Hebei, Beijing, and Tianjin is decreasing. Using the dynamic regional drought process identification method, a total of 97 regional drought processes have been identified in the study area since 1961. Using the percentile method to divide the intensity index of regional drought processes, threshold values corresponding to different intensity levels are obtained, and a total of 4 "extremely strong", 15 "strong", 30 "relatively strong", and 48 "moderate" regional drought processes occur in the study area. The strongest three regional drought processes occurred in 1968, 2001, and 1997, and the differences in circulation characteristics led to significant differences in the spatial and temporal distribution of drought days and the proportion of drought stations at different levels among the three processes. Among the 97 regional drought processes in the study area, 54.6% are caused by drought in the water source area but not in the water receiving area, which is beneficial for engineering water diversion. At the same time, in some years, the entire region is uniformly dry or the water source area is dry while the water receiving area is not dry, which is not conducive to engineering water diversion. Therefore, water resource scheduling of the middle route project of South-to-North Water Diversion Project needs to carry out targeted water diversion work based on the actual situation.
The study of drought in the water source and receiving areas of the middle route project of South-to-North Water Diversion Project is of great significance for the water resource scheduling and operation management of the project. Based on the NCEP-NCAR reanalysis data and the daily average temperature, precipitation, and meteorological drought composite index of all meteorological stations in the water source and receiving areas of middle route project of South to North Water Diversion Project from 1961 to 2023, this article conducts identification and evaluation of regional drought processes in water source area and water receiving area. The results show that the annual values of drought days in the water source area and water receiving area are 101 days and 114 days, respectively, showing an overall spatial distribution characteristic of "more in the middle and less at both ends". The northern part of Henan and the southern part of Hebei in the water receiving area are high-value areas for drought days. The number of drought days in most of the water source areas, most of the water receiving areas in Henan, and eastern Hebei is increasing, while the number of drought days in most of the water receiving areas in northern, western, and southern Hebei, Beijing, and Tianjin is decreasing. Using the dynamic regional drought process identification method, a total of 97 regional drought processes have been identified in the study area since 1961. Using the percentile method to divide the intensity index of regional drought processes, threshold values corresponding to different intensity levels are obtained, and a total of 4 "extremely strong", 15 "strong", 30 "relatively strong", and 48 "moderate" regional drought processes occur in the study area. The strongest three regional drought processes occurred in 1968, 2001, and 1997, and the differences in circulation characteristics led to significant differences in the spatial and temporal distribution of drought days and the proportion of drought stations at different levels among the three processes. Among the 97 regional drought processes in the study area, 54.6% are caused by drought in the water source area but not in the water receiving area, which is beneficial for engineering water diversion. At the same time, in some years, the entire region is uniformly dry or the water source area is dry while the water receiving area is not dry, which is not conducive to engineering water diversion. Therefore, water resource scheduling of the middle route project of South-to-North Water Diversion Project needs to carry out targeted water diversion work based on the actual situation.
Available online: April 17, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.041601
Abstract:
Based on the monthly rainfall of 643 stations in China, NCEP reanalysis data and NOAA ERSST sea surface temperature data from 1961 to 2023, impacts of early and late onset of El Ni?o on summer precipitation in China are analyzed. The results are as followed. Westerly wind anomalies in the equatorial west-central Pacific are more pronounced in June-August of years with early El Ni?o onset than in years with late El Ni?o onset, resulting in a more obvious warming of the sea surface temperature in the equatorial east-central Pacific in earlier onset years, the sea surface temperature in the quarter continues to rise. However, the positive anomaly of sea surface temperature in the equatorial east-central Pacific Ocean in the later onset years is not obvious and changes slowly. There is obvious differences in summer precipitation in central and eastern China between the El Ni?o earlier onset years and the El Ni?o later onset years, especially in July and August. In the El Ni?o earlier onset years, the Western North Pacific anticyclone (WNPAC) generally appears around August, the summer precipitation in central and eastern China is distributed in "-+-" from south to north, with more precipitation than normal in Jianghuai Region, and less precipitation than normal in other areas. In June, the Western Pacific Ocean is an abnormal cyclone, the precipitation in most of China’s central and eastern parts is less than normal. In July, the abnormal cyclone in the Western Pacific Ocean retreats southward significantly, the precipitation in regions of the Jiangnan, Northwest and North China continues to be less than normal. And the abnormal anticyclone to the east of Japan significantly extends westward and presses southward, the southeast coastal areas of China turns to abnormal southerly winds, leading to precipitation along the southern China coast, Jianghuai basin turn to more than normal. In August, Northwest Pacific Ocean turns into an anomalous anticyclone, WNPAC begins to appear, the precipitation over the middle and lower reaches of the Yangtze River and most parts of its south is more than normal, while the precipitation in most parts of northern China is less than normal. In the later onset years, WNPAC usually appears in October or later, the Western Pacific Ocean has been an abnormal cyclone from June to August. The summer precipitation in the central and eastern regions of China is distributed in "+-+" from south to north, and the precipitation persistence characteristics of each month are obvious.
Based on the monthly rainfall of 643 stations in China, NCEP reanalysis data and NOAA ERSST sea surface temperature data from 1961 to 2023, impacts of early and late onset of El Ni?o on summer precipitation in China are analyzed. The results are as followed. Westerly wind anomalies in the equatorial west-central Pacific are more pronounced in June-August of years with early El Ni?o onset than in years with late El Ni?o onset, resulting in a more obvious warming of the sea surface temperature in the equatorial east-central Pacific in earlier onset years, the sea surface temperature in the quarter continues to rise. However, the positive anomaly of sea surface temperature in the equatorial east-central Pacific Ocean in the later onset years is not obvious and changes slowly. There is obvious differences in summer precipitation in central and eastern China between the El Ni?o earlier onset years and the El Ni?o later onset years, especially in July and August. In the El Ni?o earlier onset years, the Western North Pacific anticyclone (WNPAC) generally appears around August, the summer precipitation in central and eastern China is distributed in "-+-" from south to north, with more precipitation than normal in Jianghuai Region, and less precipitation than normal in other areas. In June, the Western Pacific Ocean is an abnormal cyclone, the precipitation in most of China’s central and eastern parts is less than normal. In July, the abnormal cyclone in the Western Pacific Ocean retreats southward significantly, the precipitation in regions of the Jiangnan, Northwest and North China continues to be less than normal. And the abnormal anticyclone to the east of Japan significantly extends westward and presses southward, the southeast coastal areas of China turns to abnormal southerly winds, leading to precipitation along the southern China coast, Jianghuai basin turn to more than normal. In August, Northwest Pacific Ocean turns into an anomalous anticyclone, WNPAC begins to appear, the precipitation over the middle and lower reaches of the Yangtze River and most parts of its south is more than normal, while the precipitation in most parts of northern China is less than normal. In the later onset years, WNPAC usually appears in October or later, the Western Pacific Ocean has been an abnormal cyclone from June to August. The summer precipitation in the central and eastern regions of China is distributed in "+-+" from south to north, and the precipitation persistence characteristics of each month are obvious.
Available online: April 16, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.041501
Abstract:
Based on the reanalysis data of atmospheric circulation field with ERA5 time resolution of hourly and horizontal resolution of 0.25 ° * 0.25 °, combined with temperature field, the Northeast cold vortex process from 1979 to 2023 was objectively identified, and the climate and climate change characteristics of the Northeast cold vortex were analyzed. The results indicate that: (1) there were more Northeast cold vortex processes in the early 1990s and mid-2000s, and relatively fewer in the 2010s; The distribution of Northeast cold vortex is highest in June and lowest in March; The average duration is 4 days, with April being the shortest and January the longest. (2) The Northeast cold vortex is mostly generated between 45 ° -60 ° N and disappears (moves out) between 40 ° -55 ° N. The center of the Northeast cold vortex is mainly concentrated between 115 ° -135 ° E and 45 ° -55 ° N. The Northeast cold vortex mainly moves towards the east and southeast. (3) To the east of 120 ° E, the average strength of the cold vortex is stronger in the northeast and weaker in the west. The intensity of Northeast cold vortex showed a significant weakening trend from 1979 to 2023; The intensity distribution of the Northeast cold vortex within the year is stronger in the cold season than in the warm season. The strength difference between the grids in the analysis area is the largest in March, and the strength difference between the grids is the smallest in June. (4) There is a significant negative correlation between the intensity of the Northeast cold vortex in the Northeast region and the temperature in most months; There is a significant positive correlation with precipitation in April and June.
Based on the reanalysis data of atmospheric circulation field with ERA5 time resolution of hourly and horizontal resolution of 0.25 ° * 0.25 °, combined with temperature field, the Northeast cold vortex process from 1979 to 2023 was objectively identified, and the climate and climate change characteristics of the Northeast cold vortex were analyzed. The results indicate that: (1) there were more Northeast cold vortex processes in the early 1990s and mid-2000s, and relatively fewer in the 2010s; The distribution of Northeast cold vortex is highest in June and lowest in March; The average duration is 4 days, with April being the shortest and January the longest. (2) The Northeast cold vortex is mostly generated between 45 ° -60 ° N and disappears (moves out) between 40 ° -55 ° N. The center of the Northeast cold vortex is mainly concentrated between 115 ° -135 ° E and 45 ° -55 ° N. The Northeast cold vortex mainly moves towards the east and southeast. (3) To the east of 120 ° E, the average strength of the cold vortex is stronger in the northeast and weaker in the west. The intensity of Northeast cold vortex showed a significant weakening trend from 1979 to 2023; The intensity distribution of the Northeast cold vortex within the year is stronger in the cold season than in the warm season. The strength difference between the grids in the analysis area is the largest in March, and the strength difference between the grids is the smallest in June. (4) There is a significant negative correlation between the intensity of the Northeast cold vortex in the Northeast region and the temperature in most months; There is a significant positive correlation with precipitation in April and June.
Available online: April 16, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.022402
Abstract:
Short duration heavy rainfall is an important unstable factor affecting the safe operation of the city. Based on the minute by minute precipitation observation data from Wuhan National meteorological station since 1950s, the sliding accumulation method was used to identify short-duration heavy rainfall events, and the rain pattern of a single rainfall event was determined by fuzzy identification method, and the fuzzy identification method is used to determine the rain pattern of every single rainfall event. In addition, the temporal and spatial characteristics of short-duration heavy rainfall in Wuhan were systematically analyzed from the aspects of occurrence frequency, intensity and rain type, and preliminarily explore the influence of urbanization on short-duration heavy rainfall . The results show that: From 1954 to 2022, the short-duration heavy rainfall events in Wuhan showed an increasing trend, which suggests that the annual frequency of heavy rainfall , annual heavy rainfall , annual maximum 60-minute heavy rainfall and annual maximum single heavy rainfall were respectively 6.9 times, 289.9mm, 98.0mm and 282.2mm, while the increasing rates were 0.3 times /10a, 16.7mm/10a, 1.4mm/10a and 0.9mm/10a, respectively. However the changing trends did not pass the 95% confidence test. Among them, the frequency and amount of annual heavy precipitation exhibit interdecadal characteristics, approximately presenting a "W" shape of "decrease increase decrease increase".The incidence and contribution rate of heavy rainfall lasting 60~120 minutes were the largest, 41.6% and 32.2%, respectively. Heavy rainfall in Wuhan mainly occurs from late June to mid-July, accounting for 33.6% of the whole year. The peak of the average minute heavy rainfall frequency occurred at 05:11-05:40, and the trough occurred at 15:58-16:47. Nevertheless, the main peak of the average minute rain intensity appeared in 16:04-17:34, and the trough could be found in 07:53-08:27. The average rain intensity during the day was greater than that at night, especially during 14-20. The average frequency of peaks and valleys per minute in spring is earlier than the annual average.In terms of individual rain patterns, the heavy rainfall at each station in Wuhan was dominated by the type Ⅰ and type Ⅳ rain patterns, while the heavy rainfall in 0-60 minutes was dominated by the type Ⅰ and type Ⅲ rain, and the heavy rainfall in more than 180 minutes contributes the most to the type IV heavy rainfall . Urbanization also played an important role in increasing the frequency and duration of heavy rainfall in Wuhan city to a certain extent, and further increased the heavy rainfall .
Short duration heavy rainfall is an important unstable factor affecting the safe operation of the city. Based on the minute by minute precipitation observation data from Wuhan National meteorological station since 1950s, the sliding accumulation method was used to identify short-duration heavy rainfall events, and the rain pattern of a single rainfall event was determined by fuzzy identification method, and the fuzzy identification method is used to determine the rain pattern of every single rainfall event. In addition, the temporal and spatial characteristics of short-duration heavy rainfall in Wuhan were systematically analyzed from the aspects of occurrence frequency, intensity and rain type, and preliminarily explore the influence of urbanization on short-duration heavy rainfall . The results show that: From 1954 to 2022, the short-duration heavy rainfall events in Wuhan showed an increasing trend, which suggests that the annual frequency of heavy rainfall , annual heavy rainfall , annual maximum 60-minute heavy rainfall and annual maximum single heavy rainfall were respectively 6.9 times, 289.9mm, 98.0mm and 282.2mm, while the increasing rates were 0.3 times /10a, 16.7mm/10a, 1.4mm/10a and 0.9mm/10a, respectively. However the changing trends did not pass the 95% confidence test. Among them, the frequency and amount of annual heavy precipitation exhibit interdecadal characteristics, approximately presenting a "W" shape of "decrease increase decrease increase".The incidence and contribution rate of heavy rainfall lasting 60~120 minutes were the largest, 41.6% and 32.2%, respectively. Heavy rainfall in Wuhan mainly occurs from late June to mid-July, accounting for 33.6% of the whole year. The peak of the average minute heavy rainfall frequency occurred at 05:11-05:40, and the trough occurred at 15:58-16:47. Nevertheless, the main peak of the average minute rain intensity appeared in 16:04-17:34, and the trough could be found in 07:53-08:27. The average rain intensity during the day was greater than that at night, especially during 14-20. The average frequency of peaks and valleys per minute in spring is earlier than the annual average.In terms of individual rain patterns, the heavy rainfall at each station in Wuhan was dominated by the type Ⅰ and type Ⅳ rain patterns, while the heavy rainfall in 0-60 minutes was dominated by the type Ⅰ and type Ⅲ rain, and the heavy rainfall in more than 180 minutes contributes the most to the type IV heavy rainfall . Urbanization also played an important role in increasing the frequency and duration of heavy rainfall in Wuhan city to a certain extent, and further increased the heavy rainfall .
Available online: April 15, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.031001
Abstract:
Based on conventional observation data, Doppler weather radar data and ERA5 reanalysis data, the physical process responsible for the enhancement and maintenance of a strong squall line affecting the Bohai Sea area during the night of July 31, 2021 was analyzed. The results show that coastal terrain and sea surface temperature were key factors affecting the intensity of squall lines. The warm water areas in the central and western Bohai Sea exhibited favorable conditions for thermal instability, and the areas with high wind speeds corresponded to the areas with high sea surface temperatures. The horn-shaped coastal terrain around the Bohai Bay exhibited the "narrow tube effect", resulting in significant wind field convergence on the windward side of the coast, which was conducive to the triggering of convection. In the early stage, the cold pool outflow formed by multi-cell storms on land converged with environmental airflow, causing the storms to propagate eastward and move into the sea. The non-uniform onshore winds caused by the complex coastal terrain of the Bohai Bay were conducive to the formation of new coastal thunderstorms. These thunderstorms merged and strengthened, ultimately evolving into squall lines. The mesoscale vortices formed by the cold pool outflow of squall lines and the environmental airflow along the northern coast of Bohai Bay promoted the propagation and strengthening of squall lines along the coastline. The development of coastal convection led to the spread of cold density towards the sea, which strengthened the intensity of the sea surface cold pool and was conducive to the development of offshore squall lines. In the process of strengthening squall lines over the sea, boundary layer frontogenesis played a crucial role. Compared with the cold pool effect, the influence of boundary layer temperature and environmental airflow was more significant, ultimately leading to the development and strengthening of squall lines in the warm water area of the Bohai Sea and their weakening and dissipation in the cold water area.
Based on conventional observation data, Doppler weather radar data and ERA5 reanalysis data, the physical process responsible for the enhancement and maintenance of a strong squall line affecting the Bohai Sea area during the night of July 31, 2021 was analyzed. The results show that coastal terrain and sea surface temperature were key factors affecting the intensity of squall lines. The warm water areas in the central and western Bohai Sea exhibited favorable conditions for thermal instability, and the areas with high wind speeds corresponded to the areas with high sea surface temperatures. The horn-shaped coastal terrain around the Bohai Bay exhibited the "narrow tube effect", resulting in significant wind field convergence on the windward side of the coast, which was conducive to the triggering of convection. In the early stage, the cold pool outflow formed by multi-cell storms on land converged with environmental airflow, causing the storms to propagate eastward and move into the sea. The non-uniform onshore winds caused by the complex coastal terrain of the Bohai Bay were conducive to the formation of new coastal thunderstorms. These thunderstorms merged and strengthened, ultimately evolving into squall lines. The mesoscale vortices formed by the cold pool outflow of squall lines and the environmental airflow along the northern coast of Bohai Bay promoted the propagation and strengthening of squall lines along the coastline. The development of coastal convection led to the spread of cold density towards the sea, which strengthened the intensity of the sea surface cold pool and was conducive to the development of offshore squall lines. In the process of strengthening squall lines over the sea, boundary layer frontogenesis played a crucial role. Compared with the cold pool effect, the influence of boundary layer temperature and environmental airflow was more significant, ultimately leading to the development and strengthening of squall lines in the warm water area of the Bohai Sea and their weakening and dissipation in the cold water area.
Available online: April 11, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.020101
Abstract:
A statistical analysis of the characteristic of typhoon track deflection relative to the steering flow in East China is conducted with the CMA tropical cyclone best track dataset and the ECMWF ERA5 reanalysis data from 1950 to 2022. The results show that: Of 54 landfall typhoons, 85.2% of the typhoon tracks deviate to the left of the steering flow at the time of landing, and the underlying surface will produce an averaged deflection angle of about 6°～7° from the steering flow. The deflection angle between the typhoon tracks and the steering flow at the landing time has a good correspondence with the thermal asymmetry parameters. Generally, a cyclone with a nearly symmetric thermal structure at the time of landing corresponds to a smaller deflection angle, while the obvious thermal asymmetric structure will increase the possibility of a large deflection angle. The underlying surface is prone to triggering asymmetric convection on the left side of the cyclone near the landing, affecting the distribution of thermal structure and causing the typhoon tracks to deviate to the left of the steering flow. The development of convection on the left side of the cyclone can sometimes decrease the thermal asymmetry parameter at the time of landing. So, more attention should be paid to the evolution of thermal asymmetry near the landing instead of the asymmetry itself for more accurate prediction of typhoon track deflection.
A statistical analysis of the characteristic of typhoon track deflection relative to the steering flow in East China is conducted with the CMA tropical cyclone best track dataset and the ECMWF ERA5 reanalysis data from 1950 to 2022. The results show that: Of 54 landfall typhoons, 85.2% of the typhoon tracks deviate to the left of the steering flow at the time of landing, and the underlying surface will produce an averaged deflection angle of about 6°～7° from the steering flow. The deflection angle between the typhoon tracks and the steering flow at the landing time has a good correspondence with the thermal asymmetry parameters. Generally, a cyclone with a nearly symmetric thermal structure at the time of landing corresponds to a smaller deflection angle, while the obvious thermal asymmetric structure will increase the possibility of a large deflection angle. The underlying surface is prone to triggering asymmetric convection on the left side of the cyclone near the landing, affecting the distribution of thermal structure and causing the typhoon tracks to deviate to the left of the steering flow. The development of convection on the left side of the cyclone can sometimes decrease the thermal asymmetry parameter at the time of landing. So, more attention should be paid to the evolution of thermal asymmetry near the landing instead of the asymmetry itself for more accurate prediction of typhoon track deflection.
Available online: April 11, 2025 , DOI: 10.7519/j.issn.1000-0526.2024.122601
Abstract:
From 29 to 30 June 2023, a local abrupt torrential rainstorm occurred in the western region of Hunan Province, but the forecasters and numerical models both failed to forecast the rainfall intensity. Based on conventional surface and upper-air observation data, Doppler radar and FY-4A data, ERA5 reanalysis data and numerical forecast products, the mesoscale characteristics and forecast difficulties of this heavy rainfall event were analyzed. The results show that this is a severe torrential rain process under the background of the northwest airflow behind the upper-level trough. The northwest airflow drives the cold air behind the northeast cold vortex to the south, and merges with the southwester warm-humid air flows strengthened at night, which leads to the occurrence of this process. The severe torrential rain is caused by a back-building and quasi-stationary meso-α-scale convective system ( MCS ), which is composed of several strongly developing γ-scale MCSs. On the doppler radar image, the MCS shows as an organized linear echo band, and the echo belongs to the warm cloud precipitation echo of low centroid and high rainfall efficiency. Under the favorable environmental background, the long-term maintenance of the boundary layer convergence line，the wind velocity pulsation of the low-level jet and the vertical structure of low-level convergence and high-level divergence lead to the initiation and organization of the convective cells, the consolidation strengthening, backward propagation of MCS and convective cell train effect are important reasons for the severe torrential rains. The significant deviations in the subjective forecast of short-term timeliness was possibly caused by the forecasting deviation of the lower troposphere dynamic and thermal fields of the numerical models, the deficiency of forecaster"s ability to correct the model forecast and the uncertainty of the heavy rainstorm forecast increased by the complex topography in western Hunan.. Therefore, it is very crucial for forecasters to use the automatic weather station data, satellite data and radar data with high spatiotemporal resolutions to analyze the changes of the mesoscale environmental conditions, strengthen the short-term nowcasting, and issue early warning signals in time.
From 29 to 30 June 2023, a local abrupt torrential rainstorm occurred in the western region of Hunan Province, but the forecasters and numerical models both failed to forecast the rainfall intensity. Based on conventional surface and upper-air observation data, Doppler radar and FY-4A data, ERA5 reanalysis data and numerical forecast products, the mesoscale characteristics and forecast difficulties of this heavy rainfall event were analyzed. The results show that this is a severe torrential rain process under the background of the northwest airflow behind the upper-level trough. The northwest airflow drives the cold air behind the northeast cold vortex to the south, and merges with the southwester warm-humid air flows strengthened at night, which leads to the occurrence of this process. The severe torrential rain is caused by a back-building and quasi-stationary meso-α-scale convective system ( MCS ), which is composed of several strongly developing γ-scale MCSs. On the doppler radar image, the MCS shows as an organized linear echo band, and the echo belongs to the warm cloud precipitation echo of low centroid and high rainfall efficiency. Under the favorable environmental background, the long-term maintenance of the boundary layer convergence line，the wind velocity pulsation of the low-level jet and the vertical structure of low-level convergence and high-level divergence lead to the initiation and organization of the convective cells, the consolidation strengthening, backward propagation of MCS and convective cell train effect are important reasons for the severe torrential rains. The significant deviations in the subjective forecast of short-term timeliness was possibly caused by the forecasting deviation of the lower troposphere dynamic and thermal fields of the numerical models, the deficiency of forecaster"s ability to correct the model forecast and the uncertainty of the heavy rainstorm forecast increased by the complex topography in western Hunan.. Therefore, it is very crucial for forecasters to use the automatic weather station data, satellite data and radar data with high spatiotemporal resolutions to analyze the changes of the mesoscale environmental conditions, strengthen the short-term nowcasting, and issue early warning signals in time.
Available online: April 01, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.012402
Abstract:
A warm sector severe convective event dominated by short-term heavy precipitation occurred in southern Anhui early in the morning of 27 May, 2023. The train effect formed by a number of north-south trend parallel meso-β scale short convections caused more than 100 mm sudden local heavy precipitation in 2 hours. The numerical simulation of this event was carried out by using WRF-EnKF, a rapid update assimilation system for service operation in Anhui Meteorological Observatory. The results show that (1) the interaction between large-scale environmental field and mesoscale convective system results in the increase of horizontal scale and intensification of several short convections. In terms of dynamic action, after the occurrence of convection, a meso-γ scale cyclonic vortex formed between the short convection and the low level jet core, causing the development of eastward convection. Meanwhile, the surface convergence line formed between the outflow of thunderstorm and the environmental wind triggers new convection in the south side of the short convection, making continuously development linearly to the south for the short convection. In terms of environmental conditions, multiple parallel low level jet cores provide favorable dynamic and thermal conditions for the development of convection. Inverse secondary circulation in the middle and upper levels occurred by the strong development of convection leads to the significant enhancement of atmospheric instability on the south side and the development of convection leads to the strengthen of deep vertical wind shear. (2) The interaction between the convections causes the maintenance of the short convection structure. Parallel convection forms parallel thunderstorm high pressure, and the interaction between the outflow of adjacent thunderstorms leads to the formation of multiple parallel positive and negative divergence pairs, thus bringing about multiple parallel zonal-vertical circulations between adjacent convections in the vertical direction. This is conducive to the maintenance and development of the structure of multiple short convections.
A warm sector severe convective event dominated by short-term heavy precipitation occurred in southern Anhui early in the morning of 27 May, 2023. The train effect formed by a number of north-south trend parallel meso-β scale short convections caused more than 100 mm sudden local heavy precipitation in 2 hours. The numerical simulation of this event was carried out by using WRF-EnKF, a rapid update assimilation system for service operation in Anhui Meteorological Observatory. The results show that (1) the interaction between large-scale environmental field and mesoscale convective system results in the increase of horizontal scale and intensification of several short convections. In terms of dynamic action, after the occurrence of convection, a meso-γ scale cyclonic vortex formed between the short convection and the low level jet core, causing the development of eastward convection. Meanwhile, the surface convergence line formed between the outflow of thunderstorm and the environmental wind triggers new convection in the south side of the short convection, making continuously development linearly to the south for the short convection. In terms of environmental conditions, multiple parallel low level jet cores provide favorable dynamic and thermal conditions for the development of convection. Inverse secondary circulation in the middle and upper levels occurred by the strong development of convection leads to the significant enhancement of atmospheric instability on the south side and the development of convection leads to the strengthen of deep vertical wind shear. (2) The interaction between the convections causes the maintenance of the short convection structure. Parallel convection forms parallel thunderstorm high pressure, and the interaction between the outflow of adjacent thunderstorms leads to the formation of multiple parallel positive and negative divergence pairs, thus bringing about multiple parallel zonal-vertical circulations between adjacent convections in the vertical direction. This is conducive to the maintenance and development of the structure of multiple short convections.
Available online: March 31, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.032901
Abstract:
South China is an important water vapor transport channel. Studying the water vapor budget in South China is essential for forecasting precipitation processes in South China and its neighboring areas, and comprehending the impact of atmospheric circulation changes on weather and climate in China. Based on ERA5 data, the variation trend of water vapor budget and its relationship with precipitation in South China during the recent 40 years (1983—2022) are analyzed. The results show that water vapor budget in South China mainly inputs from the southern and western boundaries, outputs from the northern and eastern boundaries. The net budget is negative. The water vapor budget shows declining trend, with a significant decrease in output from the eastern boundary. In the four seasons, the input and output significant declines during spring. Water vapor primarily inputs the South China region through the southwest direction of the Indian Ocean—Bay of Bengal and the southeast direction of the Western Pacific. Water vapor in the middle and lower layers (700 hPa) primarily transported from the Indian Ocean—Bay of Bengal, while water vapor in the lower layer (925 hPa) mainly originates from the Western Pacific. In the recent 40 years, water vapor transport in the Indian Ocean—Bay of Bengal and Western Pacific has weakened, and water vapor transport in the direction of northeast to southwest has appeared in South China. Water vapor transport was positively correlated with precipitation in most areas of Guangxi and Guangdong (correlation coefficient >0.6). The strengthening of water vapor transport in southwest China is the key reason of precipitation occurrence. In addition, there is a trend of wetting in the South China region, with a 2.32% increase in precipitation water vapor (PWV) during the recent 40 years, which is related to the decrease trend of total water vapor outflow in the region than that of total inflow. The results of this study can provide a reference for further understanding of water vapor budget changes and abnormal precipitation events in South China.
South China is an important water vapor transport channel. Studying the water vapor budget in South China is essential for forecasting precipitation processes in South China and its neighboring areas, and comprehending the impact of atmospheric circulation changes on weather and climate in China. Based on ERA5 data, the variation trend of water vapor budget and its relationship with precipitation in South China during the recent 40 years (1983—2022) are analyzed. The results show that water vapor budget in South China mainly inputs from the southern and western boundaries, outputs from the northern and eastern boundaries. The net budget is negative. The water vapor budget shows declining trend, with a significant decrease in output from the eastern boundary. In the four seasons, the input and output significant declines during spring. Water vapor primarily inputs the South China region through the southwest direction of the Indian Ocean—Bay of Bengal and the southeast direction of the Western Pacific. Water vapor in the middle and lower layers (700 hPa) primarily transported from the Indian Ocean—Bay of Bengal, while water vapor in the lower layer (925 hPa) mainly originates from the Western Pacific. In the recent 40 years, water vapor transport in the Indian Ocean—Bay of Bengal and Western Pacific has weakened, and water vapor transport in the direction of northeast to southwest has appeared in South China. Water vapor transport was positively correlated with precipitation in most areas of Guangxi and Guangdong (correlation coefficient >0.6). The strengthening of water vapor transport in southwest China is the key reason of precipitation occurrence. In addition, there is a trend of wetting in the South China region, with a 2.32% increase in precipitation water vapor (PWV) during the recent 40 years, which is related to the decrease trend of total water vapor outflow in the region than that of total inflow. The results of this study can provide a reference for further understanding of water vapor budget changes and abnormal precipitation events in South China.
Available online: March 26, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.032001
Abstract:
Using autumn precipitation data from 373 meteorological observation stations in West China from 1961 to 2022 and ERA5 daily reanalysis data provided by the European Centre for Medium-Range Weather Forecasts (ECMWF). This study analysed the recent changes in the characteristics of both persistent and non-persistent types of extreme precipitation events during
Using autumn precipitation data from 373 meteorological observation stations in West China from 1961 to 2022 and ERA5 daily reanalysis data provided by the European Centre for Medium-Range Weather Forecasts (ECMWF). This study analysed the recent changes in the characteristics of both persistent and non-persistent types of extreme precipitation events during
Available online: March 20, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.031902
Abstract:
Based on C-band weather radar products and multi-source observations, the persistent severe storm weather process and two major rainstorm monomers in southwest Yunnan was analyzed on 13-15 March 2023, and the results were as followed. The severe storm weather process occurred in the circulation background of the eastward retreat of the cold front on the ground, the establishment and intensification of the southwesterly rapids in the low (upper) air, and the persistent intrusion of the mid-level northwesterly flow, and the storm singletons mainly developed and intensified near the angle of the intersection of the mid- and high-altitude rapids. The continuous and stable transport of the low-level warm advection and the mid-level cold advection in southwest Yunnan intensifies the unstable stratification of the ambient atmosphere. The effective potential energy of convection is 826.6-1481.6 J·kg-1, the vertical wind shear from 0 to 3 km becomes 14.4-19.9 m·s-1, and that from 0 to 6 km becomes 27.6-34.5 m·s-1, and the unstable stratification of the high-level stratification and the strong shear environment are the main reasons for the development and maintenance of the catastrophic storms.The daytime storm was triggered by the coupling of southerly wind uplift forced by warm advection with weak surface convergence lines. The significant thermal and moisture contrast on either side of the Wuliang Mountains enhanced the storm"s development. In contrast, the nighttime storm initially formed near the mid-to-low-level baroclinic frontogenesis zone and was triggered by upslope lifting during its eastward movement, intensifying under the influence of the low-level southwesterly jet.Under the influence of diurnal variations and diverse topographic forcing, the radar echo characteristics of the storm cells exhibited distinct features. (1) Storm monomer No. 1 displayed radar echo morphologies such as an inflow notch, a bounded weak echo region (BWER), and a "V" notch, with radial velocity indicating a mesocyclone structure. During the hailfall period, the average composite reflectivity was 60.5 dBz, the average vertically integrated liquid (VIL) was 36.1 kg·m?2, and the average VIL density (VILD) was 4.0 g·m?3. In contrast, Storm monomer No. 2 exhibited a prominent rear-inflow jet (RIJ) and a forward-flank inflow notch (FIN), with more pronounced topographic responses in its echo, after crossing the Lancang River, the strong echo area, VIL, and VILD increased abruptly, with VILD rising from 1.7 g·m?3 to 4.5 g·m?3. (2) The life cycles and surface severe weather manifestations of the storm cells differed significantly. Cell 1 had a lifespan of 6 hours, accompanied by continuous hailfall during its influence period, with thunderstorm winds observed before and after its passage. The precipitation phase transitioned to a mix of hail and short-term heavy rainfall exceeding 20 mm·h?1 in the later stage. Cell 2 had a lifespan of 3 hours, with hailfall occurring only in the later stage of its development, and other types of convective weather were less intense.
Based on C-band weather radar products and multi-source observations, the persistent severe storm weather process and two major rainstorm monomers in southwest Yunnan was analyzed on 13-15 March 2023, and the results were as followed. The severe storm weather process occurred in the circulation background of the eastward retreat of the cold front on the ground, the establishment and intensification of the southwesterly rapids in the low (upper) air, and the persistent intrusion of the mid-level northwesterly flow, and the storm singletons mainly developed and intensified near the angle of the intersection of the mid- and high-altitude rapids. The continuous and stable transport of the low-level warm advection and the mid-level cold advection in southwest Yunnan intensifies the unstable stratification of the ambient atmosphere. The effective potential energy of convection is 826.6-1481.6 J·kg-1, the vertical wind shear from 0 to 3 km becomes 14.4-19.9 m·s-1, and that from 0 to 6 km becomes 27.6-34.5 m·s-1, and the unstable stratification of the high-level stratification and the strong shear environment are the main reasons for the development and maintenance of the catastrophic storms.The daytime storm was triggered by the coupling of southerly wind uplift forced by warm advection with weak surface convergence lines. The significant thermal and moisture contrast on either side of the Wuliang Mountains enhanced the storm"s development. In contrast, the nighttime storm initially formed near the mid-to-low-level baroclinic frontogenesis zone and was triggered by upslope lifting during its eastward movement, intensifying under the influence of the low-level southwesterly jet.Under the influence of diurnal variations and diverse topographic forcing, the radar echo characteristics of the storm cells exhibited distinct features. (1) Storm monomer No. 1 displayed radar echo morphologies such as an inflow notch, a bounded weak echo region (BWER), and a "V" notch, with radial velocity indicating a mesocyclone structure. During the hailfall period, the average composite reflectivity was 60.5 dBz, the average vertically integrated liquid (VIL) was 36.1 kg·m?2, and the average VIL density (VILD) was 4.0 g·m?3. In contrast, Storm monomer No. 2 exhibited a prominent rear-inflow jet (RIJ) and a forward-flank inflow notch (FIN), with more pronounced topographic responses in its echo, after crossing the Lancang River, the strong echo area, VIL, and VILD increased abruptly, with VILD rising from 1.7 g·m?3 to 4.5 g·m?3. (2) The life cycles and surface severe weather manifestations of the storm cells differed significantly. Cell 1 had a lifespan of 6 hours, accompanied by continuous hailfall during its influence period, with thunderstorm winds observed before and after its passage. The precipitation phase transitioned to a mix of hail and short-term heavy rainfall exceeding 20 mm·h?1 in the later stage. Cell 2 had a lifespan of 3 hours, with hailfall occurring only in the later stage of its development, and other types of convective weather were less intense.
Available online: March 19, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.011604
Abstract:
In view of the extremely strong extreme rainstorm process caused by Typhoon Haikui (2311) , Doksuri (2305) and Megi (1617) in the coastal area of South China, using multi-source data such as National Ground Encryption Automatic Station Data, ERA5 and GDAS reanalysis data, the HYSPLIT 5.0 trajectory model Quantitative analysis the contribution of cold air and water vapor to transport paths and their different sources, the effects of different intensity cold air cooling and warming modes and water vapor transport on extreme precipitation were compared. The results show that different cold air intensity, path and water vapor transportation effect lead to different typhoon heavy precipitated area and intensity. Heavy precipitation area of Haikui tends to be zonal type along the easterly wind under the influence of the denatured cold air that originated in Mongolia. The weak cold air on the east and west routes of Megi originated from East and Central Asia in the West Siberia, respectively. And the precipitation have meridional type of Megi along the inverted trough under the influence of cold air. Even if there is no cold air affect Doksuri, the continuous train effect caused by Doksuri lead to extreme precipitation which along the southwest jet stream. The analysis also shows that the water vapor transport in the South China Sea and the western Pacific passage between Haikui and Doksuri is dominant(the contribution rate of water vapor is 90.4 % and 100 %, respectively), Rainfall is extreme; poor water vapor transport (25.5 %) in the South China Sea and the western Pacific leads to lower precipitation intensity in Megi than in Haikui and Doksuri, but the wider cold air affects the range of Megi extreme precipitation areas.
In view of the extremely strong extreme rainstorm process caused by Typhoon Haikui (2311) , Doksuri (2305) and Megi (1617) in the coastal area of South China, using multi-source data such as National Ground Encryption Automatic Station Data, ERA5 and GDAS reanalysis data, the HYSPLIT 5.0 trajectory model Quantitative analysis the contribution of cold air and water vapor to transport paths and their different sources, the effects of different intensity cold air cooling and warming modes and water vapor transport on extreme precipitation were compared. The results show that different cold air intensity, path and water vapor transportation effect lead to different typhoon heavy precipitated area and intensity. Heavy precipitation area of Haikui tends to be zonal type along the easterly wind under the influence of the denatured cold air that originated in Mongolia. The weak cold air on the east and west routes of Megi originated from East and Central Asia in the West Siberia, respectively. And the precipitation have meridional type of Megi along the inverted trough under the influence of cold air. Even if there is no cold air affect Doksuri, the continuous train effect caused by Doksuri lead to extreme precipitation which along the southwest jet stream. The analysis also shows that the water vapor transport in the South China Sea and the western Pacific passage between Haikui and Doksuri is dominant(the contribution rate of water vapor is 90.4 % and 100 %, respectively), Rainfall is extreme; poor water vapor transport (25.5 %) in the South China Sea and the western Pacific leads to lower precipitation intensity in Megi than in Haikui and Doksuri, but the wider cold air affects the range of Megi extreme precipitation areas.
Available online: March 14, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.012301
Abstract:
An extreme torrential rain event occurred in Yichang on 22 April 2018, which was mainly caused by highly organized severe rainfall mesoscale convection system (MCS).Based on conventional observations,the data from regional automatic weather stations, radar data and ERA5 reanalysis data,we have performed the organizational characteristics and formation mechanism of extreme severe rainfall MCS.Results are as follows.(1)The extreme rainstorm event occurred under the background of weak forcing at high level and weak forcing turning into strong forcing at low level which was accompanied by strong frontogenesis.High temperature, high humidity and extremely unstable atmospheric environment were conducive to the occurrence of heavy rainfall.(2)That, the warm and wet easterly air at low level was forced to lift by the ‘C’ terrain in the east of Yichang, triggered the severe rainfall echoes in mountainous plain transition area.The warm and wet southeast or easterly wind at top of the boundary layer reverted warm trough triggered dispersed flocculent convection in the plain area from Yidu to Gongan.(3)The organization of extreme severe rainfall MCS had experienced merging stage and vortex stage.Under the influence of weak synoptic-scale forcing, MCS in mountainous plain transition area spread to southeast along the low-lying terrain, and merged along three paths with the warm area flocculent echoes from the plain to north.The third one was the continuous merger of the east-west MCS formed by the low-level east-west frontal zone and the ground convergence line,which moved toward west under the guidance of the middle and low level easterly jet, and the south-north MCS in mountainous plain transition area, which resulted in the strongest precipitation stage.The mesoscale cyclonic circulation, composed of MCS cold outflow and ambient airflow, and the latent heat of heavy rainfall heating the middle atmosphere were conducive to the organization, development and strengthening of vortex MCS. The water vapor energy transport of the low-level warm and wet easterly jet stream was conducive to the long-term maintenance of the vortex MCS. (4)The extreme heavy precipitation mainly occurred in the merging stage and the long-duration vortex stage of MCS. Synoptic-scale system forcing, low-level strong frontogenesis, mesoscale topography and positive feedback of mesoscale weather system were the important causes of the formation of this extreme severe rainfall.
An extreme torrential rain event occurred in Yichang on 22 April 2018, which was mainly caused by highly organized severe rainfall mesoscale convection system (MCS).Based on conventional observations,the data from regional automatic weather stations, radar data and ERA5 reanalysis data,we have performed the organizational characteristics and formation mechanism of extreme severe rainfall MCS.Results are as follows.(1)The extreme rainstorm event occurred under the background of weak forcing at high level and weak forcing turning into strong forcing at low level which was accompanied by strong frontogenesis.High temperature, high humidity and extremely unstable atmospheric environment were conducive to the occurrence of heavy rainfall.(2)That, the warm and wet easterly air at low level was forced to lift by the ‘C’ terrain in the east of Yichang, triggered the severe rainfall echoes in mountainous plain transition area.The warm and wet southeast or easterly wind at top of the boundary layer reverted warm trough triggered dispersed flocculent convection in the plain area from Yidu to Gongan.(3)The organization of extreme severe rainfall MCS had experienced merging stage and vortex stage.Under the influence of weak synoptic-scale forcing, MCS in mountainous plain transition area spread to southeast along the low-lying terrain, and merged along three paths with the warm area flocculent echoes from the plain to north.The third one was the continuous merger of the east-west MCS formed by the low-level east-west frontal zone and the ground convergence line,which moved toward west under the guidance of the middle and low level easterly jet, and the south-north MCS in mountainous plain transition area, which resulted in the strongest precipitation stage.The mesoscale cyclonic circulation, composed of MCS cold outflow and ambient airflow, and the latent heat of heavy rainfall heating the middle atmosphere were conducive to the organization, development and strengthening of vortex MCS. The water vapor energy transport of the low-level warm and wet easterly jet stream was conducive to the long-term maintenance of the vortex MCS. (4)The extreme heavy precipitation mainly occurred in the merging stage and the long-duration vortex stage of MCS. Synoptic-scale system forcing, low-level strong frontogenesis, mesoscale topography and positive feedback of mesoscale weather system were the important causes of the formation of this extreme severe rainfall.
Available online: March 11, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.022601
Abstract:
A cumuliform cloud with supercooled water is the condition required for the icing test flight, which is referred to as supercooled cumuliform cloud in this paper. On the basis of the cloud phase state, cloud classification and liquid water top height data from CloudSat-CALIPSO cloud products and the air temperature from ERA5 reanalysis data, focusing on the local solar afternoon data with good interannual continuity, the historical supercooled cloud sample data over China from 2006-2019 were derived, and the spatiotemporal distribution characteristics of supercooled cumuliform clouds were analyzed. The supercooled cumuliform clouds in China most occur in the eastern part of the Qinghai?Xizang Plateau and extend to central China via the Yunnan–Guizhou–Sichuan region, with an annual average occurrence frequency of 0.4. The high value areas of supercooled cumuliform clouds are more westward than that of supercooled stratiform cloud and the occurrence frequency is higher. The occurrence frequencies of the four types of supercooled cumuliform clouds in descending order were as follows: altocumulus over Southwest China, Central China, and East China; stratocumulus over the plateau and the eastern sea surface; cumulus over the southern side of the plateau; and deep convection over Yunnan, Central China, and the southeast land and sea. In winter, there are three high-value centers over Sichuan, Guizhou, the ocean over eastern China, and the Sea of Japan, while the high-value center in summer extends from the eastern part of the Qinghai–Xizang Plateau to other locations on the plateau and the surrounding mountainous areas. In addition, the interannual variation of supercooled cumuliform clouds showed significant increasing trends in January in central China, the west of Northwest China and the west of the Qinghai-Xizang Plateau.
A cumuliform cloud with supercooled water is the condition required for the icing test flight, which is referred to as supercooled cumuliform cloud in this paper. On the basis of the cloud phase state, cloud classification and liquid water top height data from CloudSat-CALIPSO cloud products and the air temperature from ERA5 reanalysis data, focusing on the local solar afternoon data with good interannual continuity, the historical supercooled cloud sample data over China from 2006-2019 were derived, and the spatiotemporal distribution characteristics of supercooled cumuliform clouds were analyzed. The supercooled cumuliform clouds in China most occur in the eastern part of the Qinghai?Xizang Plateau and extend to central China via the Yunnan–Guizhou–Sichuan region, with an annual average occurrence frequency of 0.4. The high value areas of supercooled cumuliform clouds are more westward than that of supercooled stratiform cloud and the occurrence frequency is higher. The occurrence frequencies of the four types of supercooled cumuliform clouds in descending order were as follows: altocumulus over Southwest China, Central China, and East China; stratocumulus over the plateau and the eastern sea surface; cumulus over the southern side of the plateau; and deep convection over Yunnan, Central China, and the southeast land and sea. In winter, there are three high-value centers over Sichuan, Guizhou, the ocean over eastern China, and the Sea of Japan, while the high-value center in summer extends from the eastern part of the Qinghai–Xizang Plateau to other locations on the plateau and the surrounding mountainous areas. In addition, the interannual variation of supercooled cumuliform clouds showed significant increasing trends in January in central China, the west of Northwest China and the west of the Qinghai-Xizang Plateau.
Available online: March 10, 2025 , DOI: 10.7519/j.issn.1000-0526.2024.122602
Abstract:
This study investigates the evolution mechanism of a long-life convective-scale updraft in outer rainband of numerically simulated sheared tropical cyclone (TC). The updraft originates on the downshear right quadrant of outer rainband within a sheared TC with a lifespan of 2.5-hour. This updraft undergoes two intensification processes and displays complex evolutionary characteristics with two peaks in vertical mass flux. Results show that strong localized vertical wind shear and low-level high-value equivalent potential temperature are the main favorable environmental factors maintaining an updraft long life cycle. The strengthening and weakening of neighboring convective cells lead to different responses to updraft intensity by adjusting the variation of local equivalent potential temperature. The vertical momentum budget suggests that an updraft is growing when it is dominated by positive buoyancy pressure gradient acceleration and positive thermal buoyancy, yet there are differences between the two strengthening mechanisms. In the first intensification stage, the development of neighboring convective cells cause an increase in the equivalent potential temperature at lower levels. Moreover, the increase in updraft tilt and the latent heating lead to a significant increase in thermal buoyancy, resulting in a larger vertical velocity. In the early second intensification stage, the occurrence and development of new convective cells in the vicinity of the focused updraft induce an increase in localized equivalent potential temperature. Subsequently, however, the mature and dissipation of these neighboring convective cells lead to downward motion stronger and localized equivalent potential temperature decrease, resulting in smaller thermal buoyancy and smaller vertical velocity. Analogous to the weakening mechanism of convective cells in mid-latitudes, during the weakening phase, the focused updraft exhibits a decrease in tilt, and then force a downdraft directly beneath it. This downdraft and downdrafts of neighboring convective cells carry low-value equivalent potential temperature toward the lower layers to form a surface cold pool. Consequently, thermal buoyancy tends to decrease with decreasing equivalent potential temperature at lower layers, which suppress the growth of the focused updraft. In addition, the negative contribution of water loading is harmful to the development of the focused updraft. The imbalance between thermal buoyancy, buoyancy pressure gradient acceleration, and water loading constitute the primary physical mechanism responsible for the prolonged evolution of the updraft. However, a tilted updraft structure can also influence its own development.
This study investigates the evolution mechanism of a long-life convective-scale updraft in outer rainband of numerically simulated sheared tropical cyclone (TC). The updraft originates on the downshear right quadrant of outer rainband within a sheared TC with a lifespan of 2.5-hour. This updraft undergoes two intensification processes and displays complex evolutionary characteristics with two peaks in vertical mass flux. Results show that strong localized vertical wind shear and low-level high-value equivalent potential temperature are the main favorable environmental factors maintaining an updraft long life cycle. The strengthening and weakening of neighboring convective cells lead to different responses to updraft intensity by adjusting the variation of local equivalent potential temperature. The vertical momentum budget suggests that an updraft is growing when it is dominated by positive buoyancy pressure gradient acceleration and positive thermal buoyancy, yet there are differences between the two strengthening mechanisms. In the first intensification stage, the development of neighboring convective cells cause an increase in the equivalent potential temperature at lower levels. Moreover, the increase in updraft tilt and the latent heating lead to a significant increase in thermal buoyancy, resulting in a larger vertical velocity. In the early second intensification stage, the occurrence and development of new convective cells in the vicinity of the focused updraft induce an increase in localized equivalent potential temperature. Subsequently, however, the mature and dissipation of these neighboring convective cells lead to downward motion stronger and localized equivalent potential temperature decrease, resulting in smaller thermal buoyancy and smaller vertical velocity. Analogous to the weakening mechanism of convective cells in mid-latitudes, during the weakening phase, the focused updraft exhibits a decrease in tilt, and then force a downdraft directly beneath it. This downdraft and downdrafts of neighboring convective cells carry low-value equivalent potential temperature toward the lower layers to form a surface cold pool. Consequently, thermal buoyancy tends to decrease with decreasing equivalent potential temperature at lower layers, which suppress the growth of the focused updraft. In addition, the negative contribution of water loading is harmful to the development of the focused updraft. The imbalance between thermal buoyancy, buoyancy pressure gradient acceleration, and water loading constitute the primary physical mechanism responsible for the prolonged evolution of the updraft. However, a tilted updraft structure can also influence its own development.
Available online: February 28, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.010203
Abstract:
By using automatic station, reanalysis data, lightning location and multi-band radar, the environmental conditions and severe storm structure of the winter elevated thunderstorm in Zhejiang Province on February 21, 2024 were analyzed. The results show that: This process occurred in front of the upper south trough and the north side of the surface cold front. The stratification configuration was "cold and wet - cold and dry - warm and wet" from bottom to top, and the low-level stratification was stable, so it belonged to a typical elevated thunderstorm. The deep inversion layer and strong vertical wind shear were conducive to the occurrence of elevated thunderstorms. The saturation pseudo-equivalent potential temperature above the inversion layer decreased with height, and the slope of the pseudoequivalent potential temperature contours in the middle layer are greater than the absolute geostrophic momentum, which mean conditional instability and conditional symmetric instability, could result to the rapidly developed convection. Severe storm was of a forward propagating type and always Leaned forward while moving. During the intense development stage of the storm, the frequency of cloud flash increased significantly, and the area of hail corresponded to the area of dense cloud flash. The cloud flash distribution height was 4～14km. The ZH core over the hail point was initially located above the 0℃ layer height, and there are many ice crystal particles in the core area, which melt during the falling process to form a mixed particle accumulation area, and fell to the ground as rain and hail.
By using automatic station, reanalysis data, lightning location and multi-band radar, the environmental conditions and severe storm structure of the winter elevated thunderstorm in Zhejiang Province on February 21, 2024 were analyzed. The results show that: This process occurred in front of the upper south trough and the north side of the surface cold front. The stratification configuration was "cold and wet - cold and dry - warm and wet" from bottom to top, and the low-level stratification was stable, so it belonged to a typical elevated thunderstorm. The deep inversion layer and strong vertical wind shear were conducive to the occurrence of elevated thunderstorms. The saturation pseudo-equivalent potential temperature above the inversion layer decreased with height, and the slope of the pseudoequivalent potential temperature contours in the middle layer are greater than the absolute geostrophic momentum, which mean conditional instability and conditional symmetric instability, could result to the rapidly developed convection. Severe storm was of a forward propagating type and always Leaned forward while moving. During the intense development stage of the storm, the frequency of cloud flash increased significantly, and the area of hail corresponded to the area of dense cloud flash. The cloud flash distribution height was 4～14km. The ZH core over the hail point was initially located above the 0℃ layer height, and there are many ice crystal particles in the core area, which melt during the falling process to form a mixed particle accumulation area, and fell to the ground as rain and hail.
Available online: February 19, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.021801
Abstract:
Based on the hourly precipitation data of 122 national meteorological stations in Shandong from 1966 to 2023, the frequency variation of heavy precipitation are analyzed. Different marginal distribution functions are used to fit the duration and amount of precipitation and the change patterns of the return periods of heavy precipitation with different durations based on Copula function are investigated. The results are as followed. There is a significant dependence relation between the duration and amount of heavy precipitation, which can be fitted well using generalized extreme values and logarithmic normal distribution functions. The Gumbel Copula and Clayton Copula functions are suitable for portraying the dependence structure of the binary variables of the short-duration heavy precipitation in Shandong, while the Clayton Copula function is more appropriate when the precipitation lasts more than 8 h. The return period estimated by daily precipitation may seriously underestimate the hazard of short-duration heavy precipitation. For a short-duration heavy precipitation event under the same hazard-bearing condition, the shorter the duration, the longer the joint return period. The high-value areas of joint return period estimated by the Copula function gradually narrow down from the east and the south of Shandong to the east of Shandong with the increase of precipitation duration, and especially, the hazard of heavy precipitation that comes along once every 60 years is higher in the east and the south of Shandong. This method can more scientifically describe the disaster risks of heavy precipitation in different scenarios, especially in the short-duration heavy precipitation scenario, providing scientific reference for disaster prevention and mitigation planning and disaster risk managing in Shandong.
Based on the hourly precipitation data of 122 national meteorological stations in Shandong from 1966 to 2023, the frequency variation of heavy precipitation are analyzed. Different marginal distribution functions are used to fit the duration and amount of precipitation and the change patterns of the return periods of heavy precipitation with different durations based on Copula function are investigated. The results are as followed. There is a significant dependence relation between the duration and amount of heavy precipitation, which can be fitted well using generalized extreme values and logarithmic normal distribution functions. The Gumbel Copula and Clayton Copula functions are suitable for portraying the dependence structure of the binary variables of the short-duration heavy precipitation in Shandong, while the Clayton Copula function is more appropriate when the precipitation lasts more than 8 h. The return period estimated by daily precipitation may seriously underestimate the hazard of short-duration heavy precipitation. For a short-duration heavy precipitation event under the same hazard-bearing condition, the shorter the duration, the longer the joint return period. The high-value areas of joint return period estimated by the Copula function gradually narrow down from the east and the south of Shandong to the east of Shandong with the increase of precipitation duration, and especially, the hazard of heavy precipitation that comes along once every 60 years is higher in the east and the south of Shandong. This method can more scientifically describe the disaster risks of heavy precipitation in different scenarios, especially in the short-duration heavy precipitation scenario, providing scientific reference for disaster prevention and mitigation planning and disaster risk managing in Shandong.
Available online: February 18, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.011603
Abstract:
On August 13, 2022, a local severe convection occurred near the coast of Shanghai under the control of Western Pacific subtropical high. This event displayed characteristics of a short life span, strong local manifestation, and high intensity. Using data from minute-level ground automatic weather stations, FY-4A geostationary meteorological satellite visible light cloud images, and dual-polarization radar reflectivity factor, a study was conducted on the short-range forecasting techniques and causes of this local strong convection, employing diagnostic variables such as Q vector, perturbation dew point temperature and perturbation temperature. The findings are as follows:(1) The occurrence of precipitation at the ground level was identified as the sign of local strong convective events. By analyzing radar reflectivity factor, satellite visible light cloud images, and Q vector divergence combined with perturbation dew point temperature and perturbation temperature data from ground automatic weather stations, advanced warnings of the convective event could be issued 23, 70, and 100 minutes in advance, respectively. This integrated monitoring and mutual verification of the atmospheric, satellite, and ground observations not only improved the lead time of early warnings for local severe convection but also reduced missed detections. (2) Under the control of the Western Pacific subtropical high-pressure system, temperatures exceeding 35 ℃, combined with the perturbations in temperature and dew point near the urban area, provided favorable thermodynamic conditions for the initiation of deep convection. Simultaneously, differences in land and water underlying characteristics led to higher temperatures on urban land compared to the adjacent Yangtze River water, generating onshore winds. On one hand, this process experienced abrupt changes in land-water underlying characteristics and complex urban land surfaces, causing convergence of wind direction and speed. On the other hand, the convergence of warm and cold air led to atmospheric instability, providing favorable local dynamic forcing conditions. (3) Further analysis reveals that the appearance of significant Q vector divergence convergence at the surface, persisting until surface precipitation occurs, indicates the generation of vertical upward motion due to the dynamic and thermal forcing at the surface. Furthermore, the interaction between the sea breeze front and the convergence-induced updrafts from the urban heat island results in local severe convection.
On August 13, 2022, a local severe convection occurred near the coast of Shanghai under the control of Western Pacific subtropical high. This event displayed characteristics of a short life span, strong local manifestation, and high intensity. Using data from minute-level ground automatic weather stations, FY-4A geostationary meteorological satellite visible light cloud images, and dual-polarization radar reflectivity factor, a study was conducted on the short-range forecasting techniques and causes of this local strong convection, employing diagnostic variables such as Q vector, perturbation dew point temperature and perturbation temperature. The findings are as follows:(1) The occurrence of precipitation at the ground level was identified as the sign of local strong convective events. By analyzing radar reflectivity factor, satellite visible light cloud images, and Q vector divergence combined with perturbation dew point temperature and perturbation temperature data from ground automatic weather stations, advanced warnings of the convective event could be issued 23, 70, and 100 minutes in advance, respectively. This integrated monitoring and mutual verification of the atmospheric, satellite, and ground observations not only improved the lead time of early warnings for local severe convection but also reduced missed detections. (2) Under the control of the Western Pacific subtropical high-pressure system, temperatures exceeding 35 ℃, combined with the perturbations in temperature and dew point near the urban area, provided favorable thermodynamic conditions for the initiation of deep convection. Simultaneously, differences in land and water underlying characteristics led to higher temperatures on urban land compared to the adjacent Yangtze River water, generating onshore winds. On one hand, this process experienced abrupt changes in land-water underlying characteristics and complex urban land surfaces, causing convergence of wind direction and speed. On the other hand, the convergence of warm and cold air led to atmospheric instability, providing favorable local dynamic forcing conditions. (3) Further analysis reveals that the appearance of significant Q vector divergence convergence at the surface, persisting until surface precipitation occurs, indicates the generation of vertical upward motion due to the dynamic and thermal forcing at the surface. Furthermore, the interaction between the sea breeze front and the convergence-induced updrafts from the urban heat island results in local severe convection.
Available online: February 16, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.021401
Abstract:
Based on the weather radar equation, identify the key factors that affect the accuracy of weather radar echo intensity measurement. Radar transmission power is the key variable that is most prone to fluctuations in radar performance parameters, which affects the accuracy of radar measurement; The dynamic range of the receiver is a key indicator for measuring the stability of the receiving channel, which directly affects the measurement results of the echo power. An excellent weather radar system should have functions such as online monitoring, calibration, and correction of key performance parameters. This paper statistically analyzed data samples accumulated over the years from 12 networked radars in Guangdong, and tested the effectiveness of CINRAD/SA-D radar intensity calibration and online correction; The necessity of offline calibration of networked radar is demonstrated through the comparison and stability analysis of key performance parameters. Additionally, the first volume scan data collected when th
Based on the weather radar equation, identify the key factors that affect the accuracy of weather radar echo intensity measurement. Radar transmission power is the key variable that is most prone to fluctuations in radar performance parameters, which affects the accuracy of radar measurement; The dynamic range of the receiver is a key indicator for measuring the stability of the receiving channel, which directly affects the measurement results of the echo power. An excellent weather radar system should have functions such as online monitoring, calibration, and correction of key performance parameters. This paper statistically analyzed data samples accumulated over the years from 12 networked radars in Guangdong, and tested the effectiveness of CINRAD/SA-D radar intensity calibration and online correction; The necessity of offline calibration of networked radar is demonstrated through the comparison and stability analysis of key performance parameters. Additionally, the first volume scan data collected when th
Available online: February 08, 2025 , DOI: 10.7519/j.issn.1000-0526.2024.111501
Abstract:
A comprehensive meteorological risk early warning method for mountain torrent disasters is proposed using the fuzzy evaluation method in this paper. The method is based on the dynamic critical rainfall for mountain torrent early warning that considers soil water content saturation, then a correspondence between meteorological risk warning levels and fuzzy scores for mountain torrent disasters is established based on the fuzzy evaluation method. The weight algorithms are constructed respectively using the weighted average method, the coefficient of determination, and the relative error of peak flow. With this method , together with the fuzzy scores for meteorological risk warning calculated by using the precipitation forecasts from CMA-MESO, CMA-SH9, CMA-BJ and intelligent grid forecasting，the comprehensive meteorological risk level is determined. The results show that the hit rate of the comprehensive risk early warning results based on the fuzzy evaluation method is comparable to that of the CMA-BJ and higher than other models, the miss rate and false alarm rate are also comparable to those of the CMA-BJ and lower than other models,the TS scores are all higher than those of other models, through the application and verification of the mountain torrent disaster in Hengshui of Anyang River from 17 to 22 July 2021. This method can extend the lead time of mountain torrent prediction and improve the accuracy of early warning. This research result provides a new approach for the meteorological risk warning service of small watershed mountain torrent disasters in China.
A comprehensive meteorological risk early warning method for mountain torrent disasters is proposed using the fuzzy evaluation method in this paper. The method is based on the dynamic critical rainfall for mountain torrent early warning that considers soil water content saturation, then a correspondence between meteorological risk warning levels and fuzzy scores for mountain torrent disasters is established based on the fuzzy evaluation method. The weight algorithms are constructed respectively using the weighted average method, the coefficient of determination, and the relative error of peak flow. With this method , together with the fuzzy scores for meteorological risk warning calculated by using the precipitation forecasts from CMA-MESO, CMA-SH9, CMA-BJ and intelligent grid forecasting，the comprehensive meteorological risk level is determined. The results show that the hit rate of the comprehensive risk early warning results based on the fuzzy evaluation method is comparable to that of the CMA-BJ and higher than other models, the miss rate and false alarm rate are also comparable to those of the CMA-BJ and lower than other models,the TS scores are all higher than those of other models, through the application and verification of the mountain torrent disaster in Hengshui of Anyang River from 17 to 22 July 2021. This method can extend the lead time of mountain torrent prediction and improve the accuracy of early warning. This research result provides a new approach for the meteorological risk warning service of small watershed mountain torrent disasters in China.
Available online: January 16, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.011502
Abstract:
To provide reference for the prediction of major floods in the upper reaches of the Han River during the autumn flood season, based on NCEP/NCAR reanalysis data and conventional meteorological and hydrological observation data, the water and rainfall characteristics, rainfall response relationships, abnormal large-scale circulation patterns, and causes of flood precipitation of the Han River during the autumn flood season since the 21st century were studied. The research results showed that: ①The flood process in the Han River Basin during the autumn flood season in the 21st century gradually increased. The heavy rainfall center during the autumn flood season was mainly located in the southern and western parts of the upper reaches of the Han River. The frequency of precipitation on the southern bank was much higher than that on the northern bank, and in mountainous areas it was greater than in rivers and basins. The upstream was greater than the downstream; There were three centers: the area around Micang Mountain and Daba Mountain on the south side of the Han River Basin, the riverside valley above Ankang Reservoir, and the Danjiang River section at the southern foot of the outer mountain and the southwest slope of Funiu Mountain. ②The flood peak generally presents in three forms: single peak, double peak, and multi peak. It was feasible to judge single peak, multi peak, or bimodal floods based on precipitation intensity, time, and frequency. There was generally a pre discharge time of about 1-2 days from the occurrence of the strongest precipitation during the process period to the formation of floods.③The abnormally high precipitation during the autumn flood season in the upper reaches of the Han River was related to weather factors such as the 500hPa mid high latitude circulation pattern, the western Pacific subtropical high pressure, the southerly pressure high pressure and subtropical westerly jet, the plateau trough, the blocking high pressure and cold air activity, and water vapor transport. Under abnormal circulation conditions, when continuous rainy weather was combined with higher initial inflow of Danjiangkou Reservoir, flood peaks were likely to form in the upper reaches of the Han River.
To provide reference for the prediction of major floods in the upper reaches of the Han River during the autumn flood season, based on NCEP/NCAR reanalysis data and conventional meteorological and hydrological observation data, the water and rainfall characteristics, rainfall response relationships, abnormal large-scale circulation patterns, and causes of flood precipitation of the Han River during the autumn flood season since the 21st century were studied. The research results showed that: ①The flood process in the Han River Basin during the autumn flood season in the 21st century gradually increased. The heavy rainfall center during the autumn flood season was mainly located in the southern and western parts of the upper reaches of the Han River. The frequency of precipitation on the southern bank was much higher than that on the northern bank, and in mountainous areas it was greater than in rivers and basins. The upstream was greater than the downstream; There were three centers: the area around Micang Mountain and Daba Mountain on the south side of the Han River Basin, the riverside valley above Ankang Reservoir, and the Danjiang River section at the southern foot of the outer mountain and the southwest slope of Funiu Mountain. ②The flood peak generally presents in three forms: single peak, double peak, and multi peak. It was feasible to judge single peak, multi peak, or bimodal floods based on precipitation intensity, time, and frequency. There was generally a pre discharge time of about 1-2 days from the occurrence of the strongest precipitation during the process period to the formation of floods.③The abnormally high precipitation during the autumn flood season in the upper reaches of the Han River was related to weather factors such as the 500hPa mid high latitude circulation pattern, the western Pacific subtropical high pressure, the southerly pressure high pressure and subtropical westerly jet, the plateau trough, the blocking high pressure and cold air activity, and water vapor transport. Under abnormal circulation conditions, when continuous rainy weather was combined with higher initial inflow of Danjiangkou Reservoir, flood peaks were likely to form in the upper reaches of the Han River.
Available online: January 14, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.011001
Abstract:
To obtain the X-band dual-polarization radar characteristics of hail in the southwestern Yunnan, a statistical analysis method was used to analyze 22 hail sample data detected by the Menglian X-band dual-polarization radar.The results show that hailstorm cells have the following characteristics:Maximum horizontal reflectivity factor (ZH) ≥58 dBz;The 45 dBz echo development height (H45) ≥7.1 km, with a height difference between H45 and the wet-bulb 0℃ level ≥3.3 km;86% of hail cells have H45 exceeding the height of the -20°C layer;The 50 dBz echo development height (H50) ≥5.7 km, with a height difference between H50 and the -20℃ level ranging from -1.2 to 2.7 km;Vertical integrated liquid water content (VIL) density ≥2.8 g·m-3, and the VIL increased by 4.7–18.3 kg·m-2 in the volume scan preceding hailfall.Differential reflectivity (ZDR) and specific differential phase (KDP) average and median values, above 0℃ layer, concentrated near 0 value, predominantly negative; below 0℃layer within 1 km, transition from negative to positive values, gradually increasing with height decrease, maximum in the near-surface layer, reaching approximately 1.5 dB and 0.7 °/km respectively. The range of values for each parameter above the 0℃ layer, ZDR -1.92 to 1.35 dB, KDP -1.97 to 1.29 °/km, correlation coefficient (CC) 0.86 to 0.99; below the 0℃ layer, ZDR -1.92 to 3.74 dB, KDP -2.98 to 2.66 °/km, CC 0.79 to 0.98.The research results provide a reference for the detection and identification of hail characteristics by the X-band dual-polarization radar in the southwestern Yunnan region.
To obtain the X-band dual-polarization radar characteristics of hail in the southwestern Yunnan, a statistical analysis method was used to analyze 22 hail sample data detected by the Menglian X-band dual-polarization radar.The results show that hailstorm cells have the following characteristics:Maximum horizontal reflectivity factor (ZH) ≥58 dBz;The 45 dBz echo development height (H45) ≥7.1 km, with a height difference between H45 and the wet-bulb 0℃ level ≥3.3 km;86% of hail cells have H45 exceeding the height of the -20°C layer;The 50 dBz echo development height (H50) ≥5.7 km, with a height difference between H50 and the -20℃ level ranging from -1.2 to 2.7 km;Vertical integrated liquid water content (VIL) density ≥2.8 g·m-3, and the VIL increased by 4.7–18.3 kg·m-2 in the volume scan preceding hailfall.Differential reflectivity (ZDR) and specific differential phase (KDP) average and median values, above 0℃ layer, concentrated near 0 value, predominantly negative; below 0℃layer within 1 km, transition from negative to positive values, gradually increasing with height decrease, maximum in the near-surface layer, reaching approximately 1.5 dB and 0.7 °/km respectively. The range of values for each parameter above the 0℃ layer, ZDR -1.92 to 1.35 dB, KDP -1.97 to 1.29 °/km, correlation coefficient (CC) 0.86 to 0.99; below the 0℃ layer, ZDR -1.92 to 3.74 dB, KDP -2.98 to 2.66 °/km, CC 0.79 to 0.98.The research results provide a reference for the detection and identification of hail characteristics by the X-band dual-polarization radar in the southwestern Yunnan region.
Available online: January 13, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.011301
Abstract:
Based on the prediction results of Beijing Climate Center-climate prediction system version 3-subseasonal to seasonal version 2 (BCC-CPSv3-S2Sv2), various evaluation and test methods are used to test the prediction effect of the model in the flood season of the Yangtze River Basin, and to evaluate the prediction skills of daily/ten-day precipitation in the flood season of the Yangtze River Basin. The model error characteristics are studied, and the available forecasting time-scale of model precipitation is analyzed. The results show that the model has systematically overestimated the precipitation in flood season in the Yangtze River Basin as a whole, and the prediction skill in the middle and lower reaches of the Yangtze River is higher than that in the upper reaches of the Yangtze River, and the prediction effect in August is significantly better than that in June and July; the prediction skill of the model is improved with the approaching of the starting time. The effective prediction time of the model for the daily quantitative prediction of the flood season in the Yangtze River Basin is about ten days, and the qualitative prediction of the precipitation anomaly in the flood season is similar: the prediction skill of ten days in advance is the highest, and the prediction of twenty to thirty days in advance also has some reference value. In addition, the model"s prediction skill under the less rain scenario is better than that under the more rain scenario, but its prediction ability for extreme climate events is still relatively weak.
Based on the prediction results of Beijing Climate Center-climate prediction system version 3-subseasonal to seasonal version 2 (BCC-CPSv3-S2Sv2), various evaluation and test methods are used to test the prediction effect of the model in the flood season of the Yangtze River Basin, and to evaluate the prediction skills of daily/ten-day precipitation in the flood season of the Yangtze River Basin. The model error characteristics are studied, and the available forecasting time-scale of model precipitation is analyzed. The results show that the model has systematically overestimated the precipitation in flood season in the Yangtze River Basin as a whole, and the prediction skill in the middle and lower reaches of the Yangtze River is higher than that in the upper reaches of the Yangtze River, and the prediction effect in August is significantly better than that in June and July; the prediction skill of the model is improved with the approaching of the starting time. The effective prediction time of the model for the daily quantitative prediction of the flood season in the Yangtze River Basin is about ten days, and the qualitative prediction of the precipitation anomaly in the flood season is similar: the prediction skill of ten days in advance is the highest, and the prediction of twenty to thirty days in advance also has some reference value. In addition, the model"s prediction skill under the less rain scenario is better than that under the more rain scenario, but its prediction ability for extreme climate events is still relatively weak.
Available online: September 29, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.092401
Abstract:
Thunderstorm gales refer to strong winds with a wind speed ≥17 m·s-1 caused by strong convective weather systems, which are one of meso-scale and micro-scale strong convective weather that causes huge disasters. Understanding their formation mechanisms and conducting accurate nowcasting and early warning are the keys to disaster prevention and mitigation. This paper summarizes the existing studies on the formation mechanisms and nowcasting of thunderstorm gales, including synoptic patterns, environmental characteristics, different formation mechanisms and windstorm morphologies, as well as nowcasting technology. Most thunderstorm gales are generated in supercells, squall lines, and bow echoes through strong downdraft, gust front, momentum transmission, horizontal pressure gradient between outflow and ambient wind, dynamic forcing and superimposed effect of mesoscale vortex, and pumping effect of updraft on low-level warm and moist inflow, etc. On the basis of above review, the difficulties and much-need issues of the formation mechanisms and nowcasting of thunderstorm gales are discussed.
Thunderstorm gales refer to strong winds with a wind speed ≥17 m·s-1 caused by strong convective weather systems, which are one of meso-scale and micro-scale strong convective weather that causes huge disasters. Understanding their formation mechanisms and conducting accurate nowcasting and early warning are the keys to disaster prevention and mitigation. This paper summarizes the existing studies on the formation mechanisms and nowcasting of thunderstorm gales, including synoptic patterns, environmental characteristics, different formation mechanisms and windstorm morphologies, as well as nowcasting technology. Most thunderstorm gales are generated in supercells, squall lines, and bow echoes through strong downdraft, gust front, momentum transmission, horizontal pressure gradient between outflow and ambient wind, dynamic forcing and superimposed effect of mesoscale vortex, and pumping effect of updraft on low-level warm and moist inflow, etc. On the basis of above review, the difficulties and much-need issues of the formation mechanisms and nowcasting of thunderstorm gales are discussed.
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2012,38(12):1482-1491, DOI: 10.7519/j.issn.1000-0526.2012.12.005
Abstract:
By using the conventional meteorological data, Doppler radar data and NCEP/NCAR reanalysis data, the characteristics of Doppler radar’s reflectivity, environmental condition and trigger mechanism of the heavy rain are analyzed and compared between two abrupt heavy rain processes occurring in Sichuan Basin on 3 July (7.3) and 23 July (7.23) 2011. The results show that: the “7.3” heavy rain happened under a typical circulation background, and moisture transporting to the heavy rain area from the South China Sea was smoothly, thus the heavy rainfall maintained so long, but the “7.23” heavy rain occurred behind the upper cold vortex, and convective unstable energy was abundant and vertical wind shear was strong, thus this heavy rain process happened with hail and thunderstorm weather accompanied, its radar reflectivity was 5 dBz stronger than “7.3” case and had the characteristics of severe storms such as the low level weak reflectivity and the upper echo overhang. As a whole, the non equilibrium force is contributed to the occurrence of heavy rain and it is the excited mechanism of the two heavy rainfalls, and the change of the divergence evolvement is consistent with the strength and the position of the heavy rain which would happen 6 hours later．
By using the conventional meteorological data, Doppler radar data and NCEP/NCAR reanalysis data, the characteristics of Doppler radar’s reflectivity, environmental condition and trigger mechanism of the heavy rain are analyzed and compared between two abrupt heavy rain processes occurring in Sichuan Basin on 3 July (7.3) and 23 July (7.23) 2011. The results show that: the “7.3” heavy rain happened under a typical circulation background, and moisture transporting to the heavy rain area from the South China Sea was smoothly, thus the heavy rainfall maintained so long, but the “7.23” heavy rain occurred behind the upper cold vortex, and convective unstable energy was abundant and vertical wind shear was strong, thus this heavy rain process happened with hail and thunderstorm weather accompanied, its radar reflectivity was 5 dBz stronger than “7.3” case and had the characteristics of severe storms such as the low level weak reflectivity and the upper echo overhang. As a whole, the non equilibrium force is contributed to the occurrence of heavy rain and it is the excited mechanism of the two heavy rainfalls, and the change of the divergence evolvement is consistent with the strength and the position of the heavy rain which would happen 6 hours later．
2017,43(7):769-780, DOI: 10.7519/j.issn.1000-0526.2017.07.001
Abstract:
The spatial distributions of severe convective wind (SCW) and nonsevere thunderstorms (NT) over South China, occurring between 08:00 BT and 20:00 BT during spring and summer in 2010-2014, were analyzed by using the observational data from China Meteorological Administration. And then, their environmental characteristics were compared between SCW and NT in spring and summer. It was found that SCW in summer is more frequently than that in spring and that NT in summer is about 3.6 times the counts of NT in spring. SCW events mainly concentrate in the western Guangdong to the Pearl River Delta Region. Compared to NT, SCW is generally associated with stronger baroclinity, instability and stronger dynamic forcing. The precipitable water and averaged relative humidity between 700-500 hPa of SCW tend to be higher than those of NT in spring, while the opposite is the case for the pattern in summer. In conclusion, it is obvious that the dynamic forcing for SCW in spring is much better than these in summer, while the thermal condition is more significant in summer.
The spatial distributions of severe convective wind (SCW) and nonsevere thunderstorms (NT) over South China, occurring between 08:00 BT and 20:00 BT during spring and summer in 2010-2014, were analyzed by using the observational data from China Meteorological Administration. And then, their environmental characteristics were compared between SCW and NT in spring and summer. It was found that SCW in summer is more frequently than that in spring and that NT in summer is about 3.6 times the counts of NT in spring. SCW events mainly concentrate in the western Guangdong to the Pearl River Delta Region. Compared to NT, SCW is generally associated with stronger baroclinity, instability and stronger dynamic forcing. The precipitable water and averaged relative humidity between 700-500 hPa of SCW tend to be higher than those of NT in spring, while the opposite is the case for the pattern in summer. In conclusion, it is obvious that the dynamic forcing for SCW in spring is much better than these in summer, while the thermal condition is more significant in summer.
2010,36(3):9-18, DOI: 10.7519/j.issn.1000-0526.2010.3.002
Abstract:
Potential vorticity (PV) is one of the important concepts in advanced synoptic and dynamic meteorology. This paper is a brief introduction to the theory of potential vorticity, including the concept of PV, the conservation and invertibility of PV, PV thinking, moist PV (MPV), and the application of PV theory.
Potential vorticity (PV) is one of the important concepts in advanced synoptic and dynamic meteorology. This paper is a brief introduction to the theory of potential vorticity, including the concept of PV, the conservation and invertibility of PV, PV thinking, moist PV (MPV), and the application of PV theory.
2006,32(10):64-69, DOI: 10.7519/j.issn.1000-0526.2006.10.010
Abstract:
Based on the data of CINRAD Doppler Radar which located at Xinle of Hebei Province,the hail,strong wind and heavy rainfall weather events in mid-south Hebei in 2004 are statistically analyzed.The routine radar products,such as echo reflectivity,radial velocity,Vertically Integrated Liquid(VIL)Water,hail index,mesocyclone,velocity azimuth display wind profile,etc.are used in this statistics.The results show that hail's VIL value is larger than generic thunder storm's.At the same time,greater VIL value and longer sustaining will bring about greater diameter hail and larger effect area.It is the very useful index to indicate strong wind in mesocyclone products and the wind direction sudden change in radial velocity products.A reference based on analyzing this type synoptic forecast with radar system in future is proposed.
Based on the data of CINRAD Doppler Radar which located at Xinle of Hebei Province,the hail,strong wind and heavy rainfall weather events in mid-south Hebei in 2004 are statistically analyzed.The routine radar products,such as echo reflectivity,radial velocity,Vertically Integrated Liquid(VIL)Water,hail index,mesocyclone,velocity azimuth display wind profile,etc.are used in this statistics.The results show that hail's VIL value is larger than generic thunder storm's.At the same time,greater VIL value and longer sustaining will bring about greater diameter hail and larger effect area.It is the very useful index to indicate strong wind in mesocyclone products and the wind direction sudden change in radial velocity products.A reference based on analyzing this type synoptic forecast with radar system in future is proposed.
FU Jiaolan, MA Xuekuan, CHEN Tao, ZHANG Fang, ZHANG Xidi, SUN Jun, QUAN Wanqing, YANG Shunan, SHEN Xiaolin
2017,43(5):528-539, DOI: 10.7519/j.issn.1000-0526.2017.05.002
Abstract:
An extremely severe precipitation event took place in North China in 19-20 July 2016. It was characterized by large rainfall, persistent rainfall, warm cloud rainfall, strong local rainfall intensity and orographic precipitation. Its rainfall was larger than that of the extreme rainfall in 3-5 August 1996, and only next to the amount of the 2-7 August 1963 extreme rainfall event. It occurred under the circulation background of the South Asia high moving eastward, the West Pacific subtropical high moving northwestward and the low vortex in the westerlies developing in mid high latitude. The abnormal development of Huanghuai cyclone, southwest and southeast low level jets, and the abnormally abundant moisture indicates that the dynamic lifting and moisture conditions favored this severe rainfall process significantly. The whole rainfall event presented clearly the phase characteristics, and could be divided into two stages. The first stage was the orographic rainfall caused by the easterly winds ahead of the trough from the early morning to the daytime of 19 July, while the second part was produced by spiral rain bands in the north side of Huanghuai cyclone from the night of 19 to the daytime of 20 July. In the first stage, the easterly low level jet was lifted by the Taihang Mountains, which continuously triggered the convective cells along the east edge of the mountains. The weak dry and cold advection at mid level and the strong warm and wet advection at low level jointly maintained the convective instability. The cold pool generated by heavy rainfall and the mesoscale frontogenesis process created by local orographic effect provided favorable conditions for severe convections to occur continuously. The second stage rainfall was mainly related to the development of cut off vortex and Huanghuai cyclone. The blocking of the high pressure system slowed the steps of Huanghuai cyclone in North China, thus leading to the long lasting rainfall process.
An extremely severe precipitation event took place in North China in 19-20 July 2016. It was characterized by large rainfall, persistent rainfall, warm cloud rainfall, strong local rainfall intensity and orographic precipitation. Its rainfall was larger than that of the extreme rainfall in 3-5 August 1996, and only next to the amount of the 2-7 August 1963 extreme rainfall event. It occurred under the circulation background of the South Asia high moving eastward, the West Pacific subtropical high moving northwestward and the low vortex in the westerlies developing in mid high latitude. The abnormal development of Huanghuai cyclone, southwest and southeast low level jets, and the abnormally abundant moisture indicates that the dynamic lifting and moisture conditions favored this severe rainfall process significantly. The whole rainfall event presented clearly the phase characteristics, and could be divided into two stages. The first stage was the orographic rainfall caused by the easterly winds ahead of the trough from the early morning to the daytime of 19 July, while the second part was produced by spiral rain bands in the north side of Huanghuai cyclone from the night of 19 to the daytime of 20 July. In the first stage, the easterly low level jet was lifted by the Taihang Mountains, which continuously triggered the convective cells along the east edge of the mountains. The weak dry and cold advection at mid level and the strong warm and wet advection at low level jointly maintained the convective instability. The cold pool generated by heavy rainfall and the mesoscale frontogenesis process created by local orographic effect provided favorable conditions for severe convections to occur continuously. The second stage rainfall was mainly related to the development of cut off vortex and Huanghuai cyclone. The blocking of the high pressure system slowed the steps of Huanghuai cyclone in North China, thus leading to the long lasting rainfall process.
Zhou Yuquan, Chen Yingying, Li Juan, Huang Yimei, He Xiaodong, Zhou Feifei, Wu Menxin, Hu Bo, Mao Jietai
2008,34(12):27-35, DOI: 10.7519/j.issn.1000-0526.2008.12.004
Abstract:
Cloud macro and micro physical characteristic parameters play an important role not only in the field of the analysis and forecast of the weather and climate, but also in the field of weather modification to identify the seeding c ondition. Based on the data from FY-2C/D stationary satellite and SBDART radiati on transfer model, associated with the sounding data and surface information, a method retrieving cloud macro and micro physical parameters is established in th is research. These parameters include cloud top height, cloud top temperature, d epth of super-cooled layer, depth of warm layer, cloud bottom height, depth of c loud, cloud optical thickness, cloud effective particle radius and cloud liquid water content. It has been run operationally. In this paper, the correlated info rmation such as physical meaning, retrieving method and technology, retrieving p rocess and data format are simply introduced. Furthermore, comparing with the ob servation of Cloudsat up to the minute, the retrieving results of main cloud par ameters are proved to be reasonable and usable. By contrast with same kind produ cts of MODIS, it also shows good corresponding relationship.
Cloud macro and micro physical characteristic parameters play an important role not only in the field of the analysis and forecast of the weather and climate, but also in the field of weather modification to identify the seeding c ondition. Based on the data from FY-2C/D stationary satellite and SBDART radiati on transfer model, associated with the sounding data and surface information, a method retrieving cloud macro and micro physical parameters is established in th is research. These parameters include cloud top height, cloud top temperature, d epth of super-cooled layer, depth of warm layer, cloud bottom height, depth of c loud, cloud optical thickness, cloud effective particle radius and cloud liquid water content. It has been run operationally. In this paper, the correlated info rmation such as physical meaning, retrieving method and technology, retrieving p rocess and data format are simply introduced. Furthermore, comparing with the ob servation of Cloudsat up to the minute, the retrieving results of main cloud par ameters are proved to be reasonable and usable. By contrast with same kind produ cts of MODIS, it also shows good corresponding relationship.
2013,39(10):1284-1292, DOI: 10.7519/j.issn.1000-0526.2013.10.006
Abstract:
Based on the fog observation data during 24-27 December 2006 (advection radiation fog), NCEP NC reanalysis data (2.5°×2.5°) and GDAS global meteorological data (1°×1°), detailed trajectory analysis of the boundary layer characteristics and water vapor transport of the fog is investigated, combined with the weather condition, meteorological elements and physical quantity field. The results show that: (1) there is thick inversion layer, even multi layer inversion throughout the dense fog event. Temperatures of different inversion tops in the middle and high levels are 2-5℃ higher than the surface temperature. The thickness of inversion layer is more than 200 m, and it gets to 500 m at 08:00 BT 26 December, indicating the atmosphere is very stable and conducive to the convergence of water vapor before the fog forms. However, it is not favorable for the divergence of water vapor after the formation of fog, which helps the development and maintenance of the fog, causing the fog to last about 64 hours with dense fog (visibility <50 m) about 37 hours; (2) The divergence of water vapor flux in low level is negative in the advection fog event. The upper air has persistent moisture convergence and the strongest moisture convergence appears at 02:00 BT 25 December, being -30×10-7 g·s-1·cm-2·hPa-1. The accumulation of low level water vapor makes fog form and develop while the divergence of water vapor flux speeds up its dissipation. 〖JP2〗The long lasting advection radiation fog is mainly caused by the continuous water vapor convergence; (3) The water vapor path is from the coastal area in easten China to Nanjing. The water vapor is continuously supplied from sea during the fog event, with the water vapor flux maximum getting to 2 g·s-1·hPa-1·cm-1. The sufficient supply and supplementary of water vapor determines the duration of the fog.
Based on the fog observation data during 24-27 December 2006 (advection radiation fog), NCEP NC reanalysis data (2.5°×2.5°) and GDAS global meteorological data (1°×1°), detailed trajectory analysis of the boundary layer characteristics and water vapor transport of the fog is investigated, combined with the weather condition, meteorological elements and physical quantity field. The results show that: (1) there is thick inversion layer, even multi layer inversion throughout the dense fog event. Temperatures of different inversion tops in the middle and high levels are 2-5℃ higher than the surface temperature. The thickness of inversion layer is more than 200 m, and it gets to 500 m at 08:00 BT 26 December, indicating the atmosphere is very stable and conducive to the convergence of water vapor before the fog forms. However, it is not favorable for the divergence of water vapor after the formation of fog, which helps the development and maintenance of the fog, causing the fog to last about 64 hours with dense fog (visibility <50 m) about 37 hours; (2) The divergence of water vapor flux in low level is negative in the advection fog event. The upper air has persistent moisture convergence and the strongest moisture convergence appears at 02:00 BT 25 December, being -30×10-7 g·s-1·cm-2·hPa-1. The accumulation of low level water vapor makes fog form and develop while the divergence of water vapor flux speeds up its dissipation. 〖JP2〗The long lasting advection radiation fog is mainly caused by the continuous water vapor convergence; (3) The water vapor path is from the coastal area in easten China to Nanjing. The water vapor is continuously supplied from sea during the fog event, with the water vapor flux maximum getting to 2 g·s-1·hPa-1·cm-1. The sufficient supply and supplementary of water vapor determines the duration of the fog.
2012,38(10):1255-1266, DOI: 10.7519/j.issn.1000-0526.2012.10.012
Abstract:
Precipitation characteristics, environment conditions, generation and development of the mesoscale convective system that brought about the extreme torrential rain in Beijing on 21 July 2012 were analyzed comprehensively in this paper by using various conventional and unconventional data. The results showed that the extreme torrential rain had the characteristics of long duration, great rainfall and wide coverage area and its process consisted of warm area precipitation and frontal precipitation. The warm area rainfall started earlier, the severe precipitation center was scattered and lasted long while the frontal rainfallprocess contained several severe rainfall centers with high precipitation efficiency, lasting a short time.Environment conditions of the mesoscale convective system that triggered this extreme severe rainfall were analyzed. The results showed that interactions of high level divergence, the wind shear and convergence with the vortex in the lower troposphere and the surface wind convergence line provided favorable environment to the severe extreme rain. The warm humid airs from the tropical and sub tropical zones converged over the torrential rain region, continuous and sufficient water vapor manifested as high atmospheric column of precipitable water and strong low level water vapor convergence and other extreme vapor conditions for the torrential rain. In addition, the intense precipitation was triggered by the vortex wind shear, wind disturbance on low level jet, surface wind convergence line and the effect of terrain under the condition of the plentiful water vapour and maintained. With the cold front moved eastward, heavy frontal rainfall was brought by the development and evolution of convective system made by the cold air and the suitable vertical wind shear.Generation and development processes of the mesoscale convective system were also studied. The findings suggested that stratiform cloud precipitation and dispersed convective precipitation occurred firstly in the precipitation process. The warm and steady stratiform cloud precipitation changed to be highly organized convectional precipitation as the cold dry air invaded. Many small scale and mesoscale convective clusters developed into mesoscale convective complex (MCC), leading to the extreme severe precipitation. Since all the directions of the echo long axis, terrain and echo movement were parallel, train effect was obviously seen in the radar echo imegery during this precipitation process. Meanwhile, the radar echo had the characteristics of backward propagation and low centroid which was similar to tropical heavy rainfalls. Finally, a series of scientific problems were proposed according to the integrated analysis on the observation data of this rare torrential rain event, such as the causes for the extreme torrential rain and the extreme rich water vapor, mechanisms for the warm area torrential rain in the north of China, the mechanism for the train effect and backward propagation, mechanisms for the organization and maintenance of the convective cells, the simulation and analysis ability of the numerical models to extreme torrential rains and so on.
Precipitation characteristics, environment conditions, generation and development of the mesoscale convective system that brought about the extreme torrential rain in Beijing on 21 July 2012 were analyzed comprehensively in this paper by using various conventional and unconventional data. The results showed that the extreme torrential rain had the characteristics of long duration, great rainfall and wide coverage area and its process consisted of warm area precipitation and frontal precipitation. The warm area rainfall started earlier, the severe precipitation center was scattered and lasted long while the frontal rainfallprocess contained several severe rainfall centers with high precipitation efficiency, lasting a short time.Environment conditions of the mesoscale convective system that triggered this extreme severe rainfall were analyzed. The results showed that interactions of high level divergence, the wind shear and convergence with the vortex in the lower troposphere and the surface wind convergence line provided favorable environment to the severe extreme rain. The warm humid airs from the tropical and sub tropical zones converged over the torrential rain region, continuous and sufficient water vapor manifested as high atmospheric column of precipitable water and strong low level water vapor convergence and other extreme vapor conditions for the torrential rain. In addition, the intense precipitation was triggered by the vortex wind shear, wind disturbance on low level jet, surface wind convergence line and the effect of terrain under the condition of the plentiful water vapour and maintained. With the cold front moved eastward, heavy frontal rainfall was brought by the development and evolution of convective system made by the cold air and the suitable vertical wind shear.Generation and development processes of the mesoscale convective system were also studied. The findings suggested that stratiform cloud precipitation and dispersed convective precipitation occurred firstly in the precipitation process. The warm and steady stratiform cloud precipitation changed to be highly organized convectional precipitation as the cold dry air invaded. Many small scale and mesoscale convective clusters developed into mesoscale convective complex (MCC), leading to the extreme severe precipitation. Since all the directions of the echo long axis, terrain and echo movement were parallel, train effect was obviously seen in the radar echo imegery during this precipitation process. Meanwhile, the radar echo had the characteristics of backward propagation and low centroid which was similar to tropical heavy rainfalls. Finally, a series of scientific problems were proposed according to the integrated analysis on the observation data of this rare torrential rain event, such as the causes for the extreme torrential rain and the extreme rich water vapor, mechanisms for the warm area torrential rain in the north of China, the mechanism for the train effect and backward propagation, mechanisms for the organization and maintenance of the convective cells, the simulation and analysis ability of the numerical models to extreme torrential rains and so on.
ZHANG Xiaoling, ZHANG Tao, LIU Xinhua, ZHOU Qingliang, CHEN Yun, ZHOU Xiaoxia, ZHENG Yongguang, ZHAO Surong
2010,36(7):143-150, DOI: 10.7519/j.issn.1000-0526.2010.7.021
Abstract:
Mesoscale severe weather forecasting ability is limited, in some sense for a lack of valid analysis on mesoscale convective systems and its favorable environments. This paper introduces the mesoscale weather chart analysis techniq ue which was tested in the National Meteorological Center (NMC). Mesoscale weath er chart analyzes the favorable environmental conditions of mesoscale convective systems based on observational data and numerical weather forecast outputs. It includes upper air composite chart and surface chart. In the upper air composite ch art, by analyzing wind, temperature, moisture, temperature change and height change, the diagnostic systems and features in all the lower, middle and upper t roposphere isobaric layers are combined into one plot, which can clearly displa y the available environments and synoptic pattern of severe convective weather. In the surface chart, the analysis contents are pressure, wind, temperature, moi sture, convective weather phenomena and all kinds of boundaries (fronts). The te st in NMC shows that mesoscale weather chart analysis is a dependable means for severe convective weather outlook forecasting.
Mesoscale severe weather forecasting ability is limited, in some sense for a lack of valid analysis on mesoscale convective systems and its favorable environments. This paper introduces the mesoscale weather chart analysis techniq ue which was tested in the National Meteorological Center (NMC). Mesoscale weath er chart analyzes the favorable environmental conditions of mesoscale convective systems based on observational data and numerical weather forecast outputs. It includes upper air composite chart and surface chart. In the upper air composite ch art, by analyzing wind, temperature, moisture, temperature change and height change, the diagnostic systems and features in all the lower, middle and upper t roposphere isobaric layers are combined into one plot, which can clearly displa y the available environments and synoptic pattern of severe convective weather. In the surface chart, the analysis contents are pressure, wind, temperature, moi sture, convective weather phenomena and all kinds of boundaries (fronts). The te st in NMC shows that mesoscale weather chart analysis is a dependable means for severe convective weather outlook forecasting.
2009,35(1):55-64, DOI: 10.7519/j.issn.1000-0526.2009.1.007
Abstract:
A strong rainstorm is analysis which occurred in Xinghua located the north of Ji angsu province on 25 July 2007. Results show that wind disaster originated from two kinds of rainstorm. One kind was the gust front which occurred at the front of the storm. Strong wind of grade 7-9 was attained when it happened. Another ki nd was the downburst arose in the multi cell storm. The original height of refl ectivity core was higher than -20℃ isotherm. It had the characteristics of conv ergence on the mid level and descending of reflectivity core. The strong wind ab ove grade 10 was attained, when the descending airflow diverged strongly on the ground. A new cell was combined with the former storm above the gust front, thus the storm enhanced. When the downburst happened, the storm weakened, and another new cell was combin ed with the former storm. The downburst happened continuously, and the impact of gust front persisted.
A strong rainstorm is analysis which occurred in Xinghua located the north of Ji angsu province on 25 July 2007. Results show that wind disaster originated from two kinds of rainstorm. One kind was the gust front which occurred at the front of the storm. Strong wind of grade 7-9 was attained when it happened. Another ki nd was the downburst arose in the multi cell storm. The original height of refl ectivity core was higher than -20℃ isotherm. It had the characteristics of conv ergence on the mid level and descending of reflectivity core. The strong wind ab ove grade 10 was attained, when the descending airflow diverged strongly on the ground. A new cell was combined with the former storm above the gust front, thus the storm enhanced. When the downburst happened, the storm weakened, and another new cell was combin ed with the former storm. The downburst happened continuously, and the impact of gust front persisted.
2014,40(2):133-145, DOI: 10.7519/j.issn.1000-0526.2014.02.001
Abstract:
By using the NCEP reanalysis data, the vapor budget of the area covered by the severe torrential rain over the northeast of North China on 21 July, 2012 is calculated according to the vapor budget equation. The results show that meridional water vapor transportation is dominant while the extremely heavy rain hits Beijing Region, where most moist vapor comes from the southern boundary below 500 hPa. The low level regional moisture convergence is consistent with the time and space when the torrential rain breaks out and develops. Above the middle level the vertical vapor transport is more prominent. Then the variation features of the vapor transport corridors and their moisture contributions are got through the HYSPLIT mode. The backward trajectory analyses illustrate two major vapor transport corridors. The moistest vapor derived from Yellow Sea and East China Sea along the low level make the main moisture contribution during the heavy precipitation. Moisture from the South China Sea and the Bay of Bengal strengthens the water vapor in the region when the heavy rain starts and develops. Also the drier vapor corridor along the high level from the northwest of China plays an important role in this case.
By using the NCEP reanalysis data, the vapor budget of the area covered by the severe torrential rain over the northeast of North China on 21 July, 2012 is calculated according to the vapor budget equation. The results show that meridional water vapor transportation is dominant while the extremely heavy rain hits Beijing Region, where most moist vapor comes from the southern boundary below 500 hPa. The low level regional moisture convergence is consistent with the time and space when the torrential rain breaks out and develops. Above the middle level the vertical vapor transport is more prominent. Then the variation features of the vapor transport corridors and their moisture contributions are got through the HYSPLIT mode. The backward trajectory analyses illustrate two major vapor transport corridors. The moistest vapor derived from Yellow Sea and East China Sea along the low level make the main moisture contribution during the heavy precipitation. Moisture from the South China Sea and the Bay of Bengal strengthens the water vapor in the region when the heavy rain starts and develops. Also the drier vapor corridor along the high level from the northwest of China plays an important role in this case.
2014,40(4):400-411, DOI: 10.7519/j.issn.1000-0526.2014.04.002
Abstract:
Based on the synoptic environment analysis of about 100 severe convection cases in China since 2000 and the reference of related literatures, from the perspectives of the three essential conditions for the development of severe convection, namely the thermal instability, lift and moisture, five basic synoptic situation configurations of severe convection in China are proposed and expounded. They are cold advection forcing category, warm advection forcing category, baroclinic frontogenesis category, quasi barotropic category and elevated thunderstorm category. The typical characteristics of the upper cold advection forcing category is that the mid upper strong cold advection above 500 hPa strengthens and reaches the boundary warm convergence zone. The warm advection forcing category is characterized by trough with special structure moving over low level strong warm and moist advection. The deep convection produced by the mid lower layer convergence of cold and warm air features the baroclinic frontogenesis category. The quasi barotropic category mostly occurs at the northern and the southern edges or the interior of summer subtropical high and the area with weak baroclinicity, where the dynamic forcing and the surface inhomogeneous local heating play major roles. The features of elevated thunderstorms are the southwest jet in 700-500 hPa lifted by boundary cold wedge and the instable energy is from above 700 hPa. The classification based on the difference of the formation mechanisms can grasp accurately the synoptic characteristics, the situation configurations, the dynamic and thermal properties and the key points in analyzing short term potential forecast, providing more technical support to further enhance the level of weather prediction.
Based on the synoptic environment analysis of about 100 severe convection cases in China since 2000 and the reference of related literatures, from the perspectives of the three essential conditions for the development of severe convection, namely the thermal instability, lift and moisture, five basic synoptic situation configurations of severe convection in China are proposed and expounded. They are cold advection forcing category, warm advection forcing category, baroclinic frontogenesis category, quasi barotropic category and elevated thunderstorm category. The typical characteristics of the upper cold advection forcing category is that the mid upper strong cold advection above 500 hPa strengthens and reaches the boundary warm convergence zone. The warm advection forcing category is characterized by trough with special structure moving over low level strong warm and moist advection. The deep convection produced by the mid lower layer convergence of cold and warm air features the baroclinic frontogenesis category. The quasi barotropic category mostly occurs at the northern and the southern edges or the interior of summer subtropical high and the area with weak baroclinicity, where the dynamic forcing and the surface inhomogeneous local heating play major roles. The features of elevated thunderstorms are the southwest jet in 700-500 hPa lifted by boundary cold wedge and the instable energy is from above 700 hPa. The classification based on the difference of the formation mechanisms can grasp accurately the synoptic characteristics, the situation configurations, the dynamic and thermal properties and the key points in analyzing short term potential forecast, providing more technical support to further enhance the level of weather prediction.
2012,38(1):1-16, DOI: 10.7519/j.issn.1000-0526.2012.01.001
Abstract:
In this paper, the modulation of atmospheric MJO on typhoon generation over the northwestern Pacific and its mechanism are first studied by using the MJO index. The results show that the MJO plays an important modulation role in typhoon generation over the northwestern Pacific: The proportion of typhoon number is 21 between active period and inactive period; During the MJO active period, the proportion of typhoon number is also 2:1 between phases 5-6 and phases 2-3 of MJO. The composite analyses of atmospheric circulation show that there are different circulation patterns over the northwestern Pacific in different phases of the MJO, which will affect the typhoon generation. In phases 5-6 (2-3), the dynamic factor and convective heating patterns over western Pacific are favorable (unfavorable) for typhoon generation. Then， the comparing analyses of the 30-60 day low frequency kinetic energy in lower and higher levels of the troposphere show that the atmospheric intraseasonal oscillation over the northwestern Pacific has a clear impact on the typhoon generation. There is an evident positive (negative) anomaly area of 30-60 day low frequency kinetic energy in the more (less) typhoon years over the northwestern Pacific east of the Philippines, which means that strong (weak) atmospheric intraseasonal oscillation (ISO) over the northwestern Pacific is favorable (unfavorable) for typhoon generation. The analyses of 200 hPa velocity potential show that there is a clear divergence (convergence) pattern over the northwestern Pacific in the more (less) typhoon years, which is favorable (unfavorable) for typhoon generation. The modulation of the intraseasonal oscillation on the typhoon tracks over the northwestern Pacific is studied by observational data analyses. We classified the main classes of typhoon tracks into 5 types as straight west moving typhoons (I), northwest moving typhoons (II), recurving to Korea/west of Japan typhoons (III), landing on Japan typhoons (IV) and recurving to the east of Japan typhoons (V). Then the composite analyses of atmospheric low-frequency wind fields at 850, 500 and 200 hPa, corresponding to the typhoon forming date, for every typhoon track are completed. The analysis results of relationships between the low-frequency (ISO) wind fields and typhoon tracks have indicated that the typhoon tracks will be affected by wind pattern of the ISO. The low frequency positive vorticity belt (the maximum value line of cyclonic vorticity) associated with low-frequency cyclone (LFC) at 850 hPa is so closely related to the typhoon track, that the maximum value line (belt) of low frequency cyclonic vorticity can be an important factor to predicate the typhoon tracks over the northwestern Pacific. And the typhoon tracks will be also affected by the ISO circulation pattern at 200 hPa, particularly the strong low frequency wind associated with low frequency anticyclone (LFAC).
In this paper, the modulation of atmospheric MJO on typhoon generation over the northwestern Pacific and its mechanism are first studied by using the MJO index. The results show that the MJO plays an important modulation role in typhoon generation over the northwestern Pacific: The proportion of typhoon number is 21 between active period and inactive period; During the MJO active period, the proportion of typhoon number is also 2:1 between phases 5-6 and phases 2-3 of MJO. The composite analyses of atmospheric circulation show that there are different circulation patterns over the northwestern Pacific in different phases of the MJO, which will affect the typhoon generation. In phases 5-6 (2-3), the dynamic factor and convective heating patterns over western Pacific are favorable (unfavorable) for typhoon generation. Then， the comparing analyses of the 30-60 day low frequency kinetic energy in lower and higher levels of the troposphere show that the atmospheric intraseasonal oscillation over the northwestern Pacific has a clear impact on the typhoon generation. There is an evident positive (negative) anomaly area of 30-60 day low frequency kinetic energy in the more (less) typhoon years over the northwestern Pacific east of the Philippines, which means that strong (weak) atmospheric intraseasonal oscillation (ISO) over the northwestern Pacific is favorable (unfavorable) for typhoon generation. The analyses of 200 hPa velocity potential show that there is a clear divergence (convergence) pattern over the northwestern Pacific in the more (less) typhoon years, which is favorable (unfavorable) for typhoon generation. The modulation of the intraseasonal oscillation on the typhoon tracks over the northwestern Pacific is studied by observational data analyses. We classified the main classes of typhoon tracks into 5 types as straight west moving typhoons (I), northwest moving typhoons (II), recurving to Korea/west of Japan typhoons (III), landing on Japan typhoons (IV) and recurving to the east of Japan typhoons (V). Then the composite analyses of atmospheric low-frequency wind fields at 850, 500 and 200 hPa, corresponding to the typhoon forming date, for every typhoon track are completed. The analysis results of relationships between the low-frequency (ISO) wind fields and typhoon tracks have indicated that the typhoon tracks will be affected by wind pattern of the ISO. The low frequency positive vorticity belt (the maximum value line of cyclonic vorticity) associated with low-frequency cyclone (LFC) at 850 hPa is so closely related to the typhoon track, that the maximum value line (belt) of low frequency cyclonic vorticity can be an important factor to predicate the typhoon tracks over the northwestern Pacific. And the typhoon tracks will be also affected by the ISO circulation pattern at 200 hPa, particularly the strong low frequency wind associated with low frequency anticyclone (LFAC).
2012,38(2):164-173, DOI: 10.7519/j.issn.1000-0526.2012.02.004
Abstract:
Many weather forecasters seem to have acquaintance with most of basic concepts or fundamental theories which are connected with severe convection, but some of them are misapplied frequently by some forecasters when they are engaged in severe convective weather analysis or forecasting argumentation. Due to the above problem, some basic concepts and fundamental theories should be explained from the view of forecasting application. The following issues are discussed in this paper. They are the relationship between humidity and water vapor content, the role of clod air during the precipitation process, the fundamental theories connected with thermal and dynamic instability, the sounding analysis related to instability parameters, the relationship between helicity or moist potential vorticity and instability, the relationship among the convergence line, lifting velocity and convective vertical movement, and the essential connection between the synoptic patterns and severe convective phenomena.
Many weather forecasters seem to have acquaintance with most of basic concepts or fundamental theories which are connected with severe convection, but some of them are misapplied frequently by some forecasters when they are engaged in severe convective weather analysis or forecasting argumentation. Due to the above problem, some basic concepts and fundamental theories should be explained from the view of forecasting application. The following issues are discussed in this paper. They are the relationship between humidity and water vapor content, the role of clod air during the precipitation process, the fundamental theories connected with thermal and dynamic instability, the sounding analysis related to instability parameters, the relationship between helicity or moist potential vorticity and instability, the relationship among the convergence line, lifting velocity and convective vertical movement, and the essential connection between the synoptic patterns and severe convective phenomena.
2011,37(10):1262-1269, DOI: 10.7519/j.issn.1000-0526.2011.10.009
Abstract:
Based on the daily precipitation data at 110 observational stations during 1961-2008 in South China， the climatic characteristics and variation of torrential rain days， rainstorm intensity and contribution which is in annual， the first and second flood seasons in South China were studied by using statistical and diagnostic methods， such as linear regression analysis， Mann Kendall test， wavelet analysis and the computation of trend coefficients. The results have shown that the annual mean torrential rain days have a decreasing trend from coastal regions to inland in South China in recent 48 years， the highest center is in Dongxing of Guangxi （14.9 d）， and the lowest center is in Longlin of Guangxi （3.2 d）. About 72% of the total torrential rain days occurred in the flood seasons with about 45% in the first season and 27% in the second season. The mean torrential rain days have increased faintly in annual， the first and second flood seasons in South China， but it is not obvious. There are the characteristics of interannual and interdecadal changes. The mean rainstorm intensity has increased faintly in annual and in the first flood season in South China. However, since 2005 it has become obviously. The mean rainstorm intensity has declined in the second flood season， but it is not obvious. The annual mean rainstorm contribution to the total rainfall has increased obviously， but the mean contribution is not obvious in the first and second flood seasons. The wavelet analysis has shown that the changes of torrential rain days， intensity and contribution which is in annual， the first and second flood seasons in South China have two significant periods of 2-3 a and 3-4 a.
Based on the daily precipitation data at 110 observational stations during 1961-2008 in South China， the climatic characteristics and variation of torrential rain days， rainstorm intensity and contribution which is in annual， the first and second flood seasons in South China were studied by using statistical and diagnostic methods， such as linear regression analysis， Mann Kendall test， wavelet analysis and the computation of trend coefficients. The results have shown that the annual mean torrential rain days have a decreasing trend from coastal regions to inland in South China in recent 48 years， the highest center is in Dongxing of Guangxi （14.9 d）， and the lowest center is in Longlin of Guangxi （3.2 d）. About 72% of the total torrential rain days occurred in the flood seasons with about 45% in the first season and 27% in the second season. The mean torrential rain days have increased faintly in annual， the first and second flood seasons in South China， but it is not obvious. There are the characteristics of interannual and interdecadal changes. The mean rainstorm intensity has increased faintly in annual and in the first flood season in South China. However, since 2005 it has become obviously. The mean rainstorm intensity has declined in the second flood season， but it is not obvious. The annual mean rainstorm contribution to the total rainfall has increased obviously， but the mean contribution is not obvious in the first and second flood seasons. The wavelet analysis has shown that the changes of torrential rain days， intensity and contribution which is in annual， the first and second flood seasons in South China have two significant periods of 2-3 a and 3-4 a.
2015,41(2):212-218, DOI: 10.7519/j.issn.1000-0526.2015.02.009
Abstract:
From 1 May to 8 June 2013 CMA Meteorological Observation Centre conducted an experiment of cloud height observations by using cloud radar (35 GHz), whose observation data are the echo power value and temporal resolution is 1 min and a ceilometer whose observation data are the back scattering intens data with 1 min temporal resolution. The result of analyzing the data observed from the 39 d experiment indicates that: (1) the data acquisition ratio of cloud radar is 26% larger than that of ceilometer; (2) the ratio is 51% in fog haze weather; (3) relatively, precipitation has more significant effect on cloud base height measured by laser ceilometer than that by cloud radar; (4) height of cloud base measured by cloud radar is almost consistent with the height by ceilometer because their average deviation is less than 300 m.
From 1 May to 8 June 2013 CMA Meteorological Observation Centre conducted an experiment of cloud height observations by using cloud radar (35 GHz), whose observation data are the echo power value and temporal resolution is 1 min and a ceilometer whose observation data are the back scattering intens data with 1 min temporal resolution. The result of analyzing the data observed from the 39 d experiment indicates that: (1) the data acquisition ratio of cloud radar is 26% larger than that of ceilometer; (2) the ratio is 51% in fog haze weather; (3) relatively, precipitation has more significant effect on cloud base height measured by laser ceilometer than that by cloud radar; (4) height of cloud base measured by cloud radar is almost consistent with the height by ceilometer because their average deviation is less than 300 m.
2014,40(7):816-826, DOI: 10.7519/j.issn.1000-0526.2014.07.005
Abstract:
In term of precipitation data of 2400 stations from 1981 to 2010, annual, seasonal and monthly distribution and evolution characteristics of rainstorm were analyzed. The results show that the processes of rainstorm have been increased evidently since 21 century especially in the south of China, but the duration is relatively short. Rainstorm days have been increased, but the amount of precipitation is not as much as in 1990s. Variation trend of the annual (monthly) precipitation amount is in accordance with that of rainstorm days, but rainfall is averagely more while the rainstorm days are less during spring rainfall phase over the south of Yangtze River. Distribution of the maximum annual rainstorm days is very similar with that of the annual mean rainstorm days, revealing the feature of more in south and east but less in north and west. Maximum annual rainstorm days are more than double of annual average rainstorm days with multi centers due to the effect of topography. The months of maximum monthly rainstorm days over different regions of the same province are incompletely same as the result of the impact of different weather systems. Generally, rainstorm days have been increased since 2000, rainstorm begins earlier, ends latter and lasts longer than before. Nowadays, as the extreme rainfall events and secondary disasters happen frequently, it is conducive for the forecast of quantitative precipitation forecast (QPF) to learn the spatio temporal distribution and evolution features of rainstorm.
In term of precipitation data of 2400 stations from 1981 to 2010, annual, seasonal and monthly distribution and evolution characteristics of rainstorm were analyzed. The results show that the processes of rainstorm have been increased evidently since 21 century especially in the south of China, but the duration is relatively short. Rainstorm days have been increased, but the amount of precipitation is not as much as in 1990s. Variation trend of the annual (monthly) precipitation amount is in accordance with that of rainstorm days, but rainfall is averagely more while the rainstorm days are less during spring rainfall phase over the south of Yangtze River. Distribution of the maximum annual rainstorm days is very similar with that of the annual mean rainstorm days, revealing the feature of more in south and east but less in north and west. Maximum annual rainstorm days are more than double of annual average rainstorm days with multi centers due to the effect of topography. The months of maximum monthly rainstorm days over different regions of the same province are incompletely same as the result of the impact of different weather systems. Generally, rainstorm days have been increased since 2000, rainstorm begins earlier, ends latter and lasts longer than before. Nowadays, as the extreme rainfall events and secondary disasters happen frequently, it is conducive for the forecast of quantitative precipitation forecast (QPF) to learn the spatio temporal distribution and evolution features of rainstorm.
2011,37(5):599-606, DOI: 10.7519/j.issn.1000-0526.2011.5.012
Abstract:
Using the diurnal snow data of 120 meteorological stations in Yunnan Province during 1961-2008, the temporal and spatial distribution characteristics and the trend of climatic change of the annual and monthly snow fall are analyzed. It is pointed out that the total trend of snow frequency and covering stations has been decreasing in Yunnan in the recent 50 years. And the annual snow frequency has declined at a mean rate of 4.5 times per year. The temporal trends of monthly snow frequency and covering stations are all negative. Moreover the reduction of snow frequency in December is the largest in magnitude, therefore, it is the most remarkable. And the reduction of snow stations in April is the largest. As far as the spatial change of the secular trend variation of annual snow frequency is concerned, the reduction of annual snow frequency is larger in Northwest Yunnan than in its northeast and east, where the reduction rate is 0.44 times per year. And the temporal changes of annual snowfall and depth of snow cover are studied, the results show that the secular trends of annual snowfall and the maximum depth of snow cover are all positive. This means that in the nearly 50 years the heavy snow frequency has increased over Yunnan Province.
Using the diurnal snow data of 120 meteorological stations in Yunnan Province during 1961-2008, the temporal and spatial distribution characteristics and the trend of climatic change of the annual and monthly snow fall are analyzed. It is pointed out that the total trend of snow frequency and covering stations has been decreasing in Yunnan in the recent 50 years. And the annual snow frequency has declined at a mean rate of 4.5 times per year. The temporal trends of monthly snow frequency and covering stations are all negative. Moreover the reduction of snow frequency in December is the largest in magnitude, therefore, it is the most remarkable. And the reduction of snow stations in April is the largest. As far as the spatial change of the secular trend variation of annual snow frequency is concerned, the reduction of annual snow frequency is larger in Northwest Yunnan than in its northeast and east, where the reduction rate is 0.44 times per year. And the temporal changes of annual snowfall and depth of snow cover are studied, the results show that the secular trends of annual snowfall and the maximum depth of snow cover are all positive. This means that in the nearly 50 years the heavy snow frequency has increased over Yunnan Province.
2014,40(4):389-399, DOI: 10.7519/j.issn.1000-0526.2014.04.001
Abstract:
Thunderstorm potential forecasting based on three ingredients has been widely accepted. This article aims to discuss some basical questions in operational forecast applications, and clarify some easily confused concepts. The content includes atmospheric instablility and convection, thunderstorms trigger mechanism and lifting and its relationship with snoptical weather system, how to deal with the three elements of the thunderstorm “enough”, the combination of pattern recognition and ingredients based forecasting methodology. Atmospheric instablility is one of the three ingredients of convection initiation, and it is also very important to thunderstorm short time forecasting and analysis. This paper discusses various mesoscale instability related to the thunderstorm, and inicates how to estimate the spatial and temporal evolution of CAPE. In addition, the definition and criterion for potential instability and symmetric instability are discussed profoundly.
Thunderstorm potential forecasting based on three ingredients has been widely accepted. This article aims to discuss some basical questions in operational forecast applications, and clarify some easily confused concepts. The content includes atmospheric instablility and convection, thunderstorms trigger mechanism and lifting and its relationship with snoptical weather system, how to deal with the three elements of the thunderstorm “enough”, the combination of pattern recognition and ingredients based forecasting methodology. Atmospheric instablility is one of the three ingredients of convection initiation, and it is also very important to thunderstorm short time forecasting and analysis. This paper discusses various mesoscale instability related to the thunderstorm, and inicates how to estimate the spatial and temporal evolution of CAPE. In addition, the definition and criterion for potential instability and symmetric instability are discussed profoundly.
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ISSN:1000-0526 CN:11-2282/P