ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 51,Issue 5,2025 Table of Contents
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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ISSN:1000-0526 CN:11-2282/P