ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 51,2025 Issue 2
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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(2):129-142, DOI: 10.7519/j.issn.1000-0526.2024.122201
Abstract:
The fuzzy logic method has been widely used and continuously improved in the classification and recognition of echoes such as ground clutter of weather radars, and has become the mainstream technology type for non-precipitation echo recognition processing of operational weather radar systems in various countries. This paper introduces the basic principle of fuzzy logic method for clutter recognition, sorts out the evolution and application of fuzzy logic method in ground clutter recognition of weather radar, and then looks into the future’s development direction and application value of this field so as to provide some references for further promoting the development of ground clutter recognition and suppression technology of weather radar.
The fuzzy logic method has been widely used and continuously improved in the classification and recognition of echoes such as ground clutter of weather radars, and has become the mainstream technology type for non-precipitation echo recognition processing of operational weather radar systems in various countries. This paper introduces the basic principle of fuzzy logic method for clutter recognition, sorts out the evolution and application of fuzzy logic method in ground clutter recognition of weather radar, and then looks into the future’s development direction and application value of this field so as to provide some references for further promoting the development of ground clutter recognition and suppression technology of weather radar.
2025,51(2):143-152, DOI: 10.7519/j.issn.1000-0526.2024.071501
Abstract:
Observational researches of aerosols and cloud microphysics have been carried out by means of aircraft carrying cloud physics detection instruments for many years in Hebei Province, China. A series of research results have been obtained and published in the fields of aerosols, cloud condensation nuclei (CCN), clouds and precipitation macro and micro structure characteristics, especially some weather modification catalytic experiments by aircraft. In this paper, the research progresses of aerosols and cloud precipitation physical observations over Hebei Province in the recent 20 years are systematically summarized. The microphysical characteristics of aerosols, CCN and clouds, such as vertical structure, spatial distribution and seasonal variation, are summarized. Four observation field campaigns for aircraft precipitation enhancement operation and the effect test are introduced in detail. The physical evidence of macro and micro physical characteristic changes in the supercooled water area before and after cloud catalysis is objectively demonstrated. In addition, the future development direction is put forward on the basis of summarizing a large number of research results, with some suggestions for aerosol-cloud physical aircraft observation and weather modification activities through aircraft catalysis in North China.
Observational researches of aerosols and cloud microphysics have been carried out by means of aircraft carrying cloud physics detection instruments for many years in Hebei Province, China. A series of research results have been obtained and published in the fields of aerosols, cloud condensation nuclei (CCN), clouds and precipitation macro and micro structure characteristics, especially some weather modification catalytic experiments by aircraft. In this paper, the research progresses of aerosols and cloud precipitation physical observations over Hebei Province in the recent 20 years are systematically summarized. The microphysical characteristics of aerosols, CCN and clouds, such as vertical structure, spatial distribution and seasonal variation, are summarized. Four observation field campaigns for aircraft precipitation enhancement operation and the effect test are introduced in detail. The physical evidence of macro and micro physical characteristic changes in the supercooled water area before and after cloud catalysis is objectively demonstrated. In addition, the future development direction is put forward on the basis of summarizing a large number of research results, with some suggestions for aerosol-cloud physical aircraft observation and weather modification activities through aircraft catalysis in North China.
2025,51(2):153-166, DOI: 10.7519/j.issn.1000-0526.2024.122202
Abstract:
The CMA Earth System Modeling and Prediction Centre is currently developing a regional ensemble prediction system with a horizontal resolution of 3 km. In view of the intricate terrain and meteorological conditions in Southwest China, coupled with the limited efficacy of the precipitation forecast products from the CMA regional model in this particular area, it is intended to place a significant emphasis on the impact of enhancing the horizontal resolution of the CMA regional ensemble prediction system on the precipitation forecast performance for the southwestern region during the research and development phase. Considering the aforementioned, this study, grounded in the CMA regional ensemble prediction system, has formulated two ensemble forecast tests with horizontal resolutions of 3 km and 10 km, respectively. Focusing on the recurrent precipitation events in the western Sichuan Basin during August 2020, a 25-day continuous test was executed. The experimental results were subsequently evaluated and comparatively analyzed. The findings reveal that the augmentation of horizontal resolution contributes significantly to the escalation of perturbation energy within the vertical layers of the troposphere, and it facilitates a more precise delineation of the forecast uncertainties associated with mesoscale and smaller-scale waves. Evaluation based on isobaric surfaces and ground meteorological parameters demonstrates that increasing the horizontal resolution helps to amplify the ensemble spread, improve the probabilistic forecasting skill for wind field, temperature and precipitation, and elevate the precision of precipitation forecases. Nonetheless, the 3 km ensemble prediction system still faces the problem of insufficient ensemble spread. The analysis of a heavy rainfall event shows that increasing the horizontal resolution facilitates more detailed simulation of multi-scale terrain and more accurate depiction of water vapor and dynamic structure in the rainstorm area, which in turn elevates the forecast performance for this event.
The CMA Earth System Modeling and Prediction Centre is currently developing a regional ensemble prediction system with a horizontal resolution of 3 km. In view of the intricate terrain and meteorological conditions in Southwest China, coupled with the limited efficacy of the precipitation forecast products from the CMA regional model in this particular area, it is intended to place a significant emphasis on the impact of enhancing the horizontal resolution of the CMA regional ensemble prediction system on the precipitation forecast performance for the southwestern region during the research and development phase. Considering the aforementioned, this study, grounded in the CMA regional ensemble prediction system, has formulated two ensemble forecast tests with horizontal resolutions of 3 km and 10 km, respectively. Focusing on the recurrent precipitation events in the western Sichuan Basin during August 2020, a 25-day continuous test was executed. The experimental results were subsequently evaluated and comparatively analyzed. The findings reveal that the augmentation of horizontal resolution contributes significantly to the escalation of perturbation energy within the vertical layers of the troposphere, and it facilitates a more precise delineation of the forecast uncertainties associated with mesoscale and smaller-scale waves. Evaluation based on isobaric surfaces and ground meteorological parameters demonstrates that increasing the horizontal resolution helps to amplify the ensemble spread, improve the probabilistic forecasting skill for wind field, temperature and precipitation, and elevate the precision of precipitation forecases. Nonetheless, the 3 km ensemble prediction system still faces the problem of insufficient ensemble spread. The analysis of a heavy rainfall event shows that increasing the horizontal resolution facilitates more detailed simulation of multi-scale terrain and more accurate depiction of water vapor and dynamic structure in the rainstorm area, which in turn elevates the forecast performance for this event.
2025,51(2):167-181, DOI: 10.7519/j.issn.1000-0526.2024.093001
Abstract:
The standard precipitation verificaiton method and the MODE （Method for Object-Based Diagnostic Evaluation） spatial method are applied to evaluate the performance of the CMA-MESO and CMA-SH9 models in predicting precipitation in eastern China in 2021 in this article. The results show that the two models have relatively high prediction skills for the second and third seasons of 2021, while the prediction skills for the first and fourth seasons are relatively low. The regional numerical models have good application potential in warm season precipitation forecasting. Based on the ETS and BIAS of the four seasons, the overall precipitation prediction skills of the CMA-MESO model in the third season are higher than those of the CMA-SH9 model, while in other seaons, the CMA-SH9 model has relatively higher prediction skills. Both models show a higher BIAS and a higher false alarm ratio in each season. Improving the shortcomings of these two aspects is an important means to enhance the precipitaiton prediction skills of regional models. The spatial verification results of torrential rain for four seasons show that CMA-MESO and CMA-SH9 models have relatively better forecasting abilities for the second and third seasons, and both of them tend to overestimate the object area of torrential rain. The CMA-SH9 model tends to overestimate the object quantile intensities of torrential rainfall in four seasons compared to observations, whereas the CMA-MESO model shows closer agreement with observations, exhibiting an overestimation only in the first season. Spatial verification of the MODE for the July 2021 severe torrential rain in Henan and Typhoon In-Fa reveals that both the CMA-MESO and CMA-SH9 models exhibit a tendency to overestimate the affected area for intense precipitation exceeding heavy torrential rain levels. Nonetheless, these models continue to underpredict the maxima of rainfall, with the CMA-SH9 model outputs more closely aligned with the observed extreme values.
The standard precipitation verificaiton method and the MODE （Method for Object-Based Diagnostic Evaluation） spatial method are applied to evaluate the performance of the CMA-MESO and CMA-SH9 models in predicting precipitation in eastern China in 2021 in this article. The results show that the two models have relatively high prediction skills for the second and third seasons of 2021, while the prediction skills for the first and fourth seasons are relatively low. The regional numerical models have good application potential in warm season precipitation forecasting. Based on the ETS and BIAS of the four seasons, the overall precipitation prediction skills of the CMA-MESO model in the third season are higher than those of the CMA-SH9 model, while in other seaons, the CMA-SH9 model has relatively higher prediction skills. Both models show a higher BIAS and a higher false alarm ratio in each season. Improving the shortcomings of these two aspects is an important means to enhance the precipitaiton prediction skills of regional models. The spatial verification results of torrential rain for four seasons show that CMA-MESO and CMA-SH9 models have relatively better forecasting abilities for the second and third seasons, and both of them tend to overestimate the object area of torrential rain. The CMA-SH9 model tends to overestimate the object quantile intensities of torrential rainfall in four seasons compared to observations, whereas the CMA-MESO model shows closer agreement with observations, exhibiting an overestimation only in the first season. Spatial verification of the MODE for the July 2021 severe torrential rain in Henan and Typhoon In-Fa reveals that both the CMA-MESO and CMA-SH9 models exhibit a tendency to overestimate the affected area for intense precipitation exceeding heavy torrential rain levels. Nonetheless, these models continue to underpredict the maxima of rainfall, with the CMA-SH9 model outputs more closely aligned with the observed extreme values.
2025,51(2):182-190, DOI: 10.7519/j.issn.1000-0526.2024.111802
Abstract:
This study employs the high-resolution operational model CMA-MESO to simulate a convective cloud precipitation process in Shandong Province by using a double-moment microphysical scheme with/without hail. The mechanism of hail microphysical effect on convective cloud precipitation and the predictive ability of this model in forecasting hail cloud precipitation are comparatively analyzed. The results show that the CMA-MESO model can simulate this convective precipitation process well. Compared with observations, the squall line life cycle in the model results is similar to the observation, and the distribution and magnitude of precipitation are close to the observation, too. The average liquid water and ice water path of the control group (without hail) in the simulated area is larger than that of the experimental group (including hail). The rising speed of the convective core area in the experimental group slightly increases during convective development but decreases at other times. When hail occurs, the melting and heat absorption in the experimental group is stronger than in the control group. This might be due to the stronger falling speed of hail compared to that of other water condensates, which suppresses the development of convection during the falling process of hail. In addition, increasing the hail amount can affect convective precipitation. The proportion of moderate rain ［1-10 mm·(24 h)-1］ area to the total precipita-tion area in the experimental group decreases, while the proportion of heavy rain and above ［>10 mm·(24 h)-1］ area to the total precipitation area slightly increases. In terms of precipitation amount, with the increased hail, there is no significant change in the intensity of medium-to-light precipitation, but the intensity of heavy rain and above increases.
This study employs the high-resolution operational model CMA-MESO to simulate a convective cloud precipitation process in Shandong Province by using a double-moment microphysical scheme with/without hail. The mechanism of hail microphysical effect on convective cloud precipitation and the predictive ability of this model in forecasting hail cloud precipitation are comparatively analyzed. The results show that the CMA-MESO model can simulate this convective precipitation process well. Compared with observations, the squall line life cycle in the model results is similar to the observation, and the distribution and magnitude of precipitation are close to the observation, too. The average liquid water and ice water path of the control group (without hail) in the simulated area is larger than that of the experimental group (including hail). The rising speed of the convective core area in the experimental group slightly increases during convective development but decreases at other times. When hail occurs, the melting and heat absorption in the experimental group is stronger than in the control group. This might be due to the stronger falling speed of hail compared to that of other water condensates, which suppresses the development of convection during the falling process of hail. In addition, increasing the hail amount can affect convective precipitation. The proportion of moderate rain ［1-10 mm·(24 h)-1］ area to the total precipita-tion area in the experimental group decreases, while the proportion of heavy rain and above ［>10 mm·(24 h)-1］ area to the total precipitation area slightly increases. In terms of precipitation amount, with the increased hail, there is no significant change in the intensity of medium-to-light precipitation, but the intensity of heavy rain and above increases.
2025,51(2):191-206, DOI: 10.7519/j.issn.1000-0526.2024.110501
Abstract:
Focusing on the thunderstorm gale process in Liaoning on 6 July 2023, based on the X-band phased array radar data, this paper analyzes the impact mechanisms of meso-γ scale vortex (MV) on merged bow echo and thunderstorm gales which occurred under the background of Northeast China cold vortex. The results show that the thunderstorm gale area in Liaoning Province was located in the southeast quadrant of the Northeast China cold vortex, influenced by low-level shear lines and low-level jet streams. The beneficial environment condition such as extreme temperature difference between 850 hPa and 500 hPa was conducive to the occurrence of thunderstorm gales. The relative humidity near the ground at night was close to 70%, which was not conducive to the formation of strong cold pools. Therefore, there was no bow-shaped pattern in squall lines and the thunderstorm gales were very scattered at this time. Subsequently, the squall line merged with the isolation storm, with shallow MV generated at the merging height, and the rear-inflow jet (RIJ) was weakened. The micro downburst near MV created a strong cold pool near the ground. Under the joint stretching effect of the rising airflow at the edge of the cold pool and the original rising airflow of the storm, the MV stretched upward and strengthened. The ZDR column formed over the MV, indicating the presence of strong updrafts in this area. Although the storm at the MV showed a bow-shaped pattern during this period, there were no thunderstorm gales below the MV. When the rotation of MV weakened, there was a rapid decrease in the scale and concentration of precipitation particles within the storm. The evaporation of precipitation led to the formation of even stronger and larger cold pools on the ground, and the fast development of RIJ below the MV, leading to the concentration of thunderstorm gales in the strong cold pool and RIJ below the MV. The ground strong winds were not caused by the strengthening of MV development, but rather the result of RIJ’s downward development and hydrometeor evaporation.
Focusing on the thunderstorm gale process in Liaoning on 6 July 2023, based on the X-band phased array radar data, this paper analyzes the impact mechanisms of meso-γ scale vortex (MV) on merged bow echo and thunderstorm gales which occurred under the background of Northeast China cold vortex. The results show that the thunderstorm gale area in Liaoning Province was located in the southeast quadrant of the Northeast China cold vortex, influenced by low-level shear lines and low-level jet streams. The beneficial environment condition such as extreme temperature difference between 850 hPa and 500 hPa was conducive to the occurrence of thunderstorm gales. The relative humidity near the ground at night was close to 70%, which was not conducive to the formation of strong cold pools. Therefore, there was no bow-shaped pattern in squall lines and the thunderstorm gales were very scattered at this time. Subsequently, the squall line merged with the isolation storm, with shallow MV generated at the merging height, and the rear-inflow jet (RIJ) was weakened. The micro downburst near MV created a strong cold pool near the ground. Under the joint stretching effect of the rising airflow at the edge of the cold pool and the original rising airflow of the storm, the MV stretched upward and strengthened. The ZDR column formed over the MV, indicating the presence of strong updrafts in this area. Although the storm at the MV showed a bow-shaped pattern during this period, there were no thunderstorm gales below the MV. When the rotation of MV weakened, there was a rapid decrease in the scale and concentration of precipitation particles within the storm. The evaporation of precipitation led to the formation of even stronger and larger cold pools on the ground, and the fast development of RIJ below the MV, leading to the concentration of thunderstorm gales in the strong cold pool and RIJ below the MV. The ground strong winds were not caused by the strengthening of MV development, but rather the result of RIJ’s downward development and hydrometeor evaporation.
2025,51(2):207-220, DOI: 10.7519/j.issn.1000-0526.2024.122301
Abstract:
Based on the NCAR/NCEP reanalysis data and conventional meteorological and hydrological observation data, 15 cases of numbered floods in the upper reaches of the Hanjiang River in the autumn flood season are taken as the research object to study the characteristics of flood peak patterns and the evolution laws of corresponding weather systems, and a weather conceptual model of flood-causing rainstorm is constructed. The results shown that during the autumn flood season, single peak flood processes occur most frequently in the upper reaches of the Hanjiang River, and the flood hydrograph has diversity. The bimodal pattern has a large flood volume, high peak, and rapid rise and fall of water level, with a mostly pointed and thin shape. The multi-peak flood has the largest volume and longest duration, with varying peak heights. The duration of the unimodal flood process is short, and the daily accumulated precipitation fluctuates greatly, with rapid peak formation, and all of them are sharp and thin. The duration of the bimodal process is generally no less than 11 d, the interval between rainstorm processes is short, the difference between the main peak and the secondary peak is small, and the peak value is more than 20 000 m3·s-1. The duration of the multi-peak precipitation process is the longest, and in the continuous cloudy and rainy weather can last for more than 20 d, but the main peak value is lower than that of the bimodal pattern. From the perspective of large-scale circulation patterns, in mid to high latitudes, there are generally three more obvious pattern adjustments in the bimodal pattern, with a larger meridional degree of circulation. There are fewer adjustments to the multi-peak circulation pattern, and the southern side of Lake Baikal is mostly characterized by small trough and ridge activities. There is no significant adjustment in the unimodal pattern. In the middle and low latitudes, the western Pacific subtropical high with multiple peaks moves most strongly westward, without typhoon or tropical cyclone activities. The bimodal subtropical high oscillates frequently from east to west, often involving tropical cyclones. The unimodal pattern is often accompanied by the merging of continental and oceanic high-pressure systems, with few activities of typhoons or tropical cyclones. The weather conceptual models of flood-causing rainstorm in the upper reaches of the Hanjiang River during the autumn flood season can be divided into five categories: high trough jet forcing (A-Ⅰ), high trough low vortex shear (A-Ⅲ), subtropical high periphery jet forcing (B-Ⅰ), subtropical high periphery southerly flow weak forcing (B-Ⅱ) and subtropical high interior low vortex shear (C-Ⅲ). Bimodal floods are mostly dominated by pattern A, while multimodal floods are mostly dominated by pattern B, with both single peak pattern A and pattern B appearing, and pattern C is only unique to single peak pattern. In addition, ground pattern Ⅰ and pattern Ⅱ are often combined with A-Ⅰ, A-Ⅲ, B-Ⅰ, etc. When the three-layer weather system is well configured, the probability of flooding will be significantly increased.
Based on the NCAR/NCEP reanalysis data and conventional meteorological and hydrological observation data, 15 cases of numbered floods in the upper reaches of the Hanjiang River in the autumn flood season are taken as the research object to study the characteristics of flood peak patterns and the evolution laws of corresponding weather systems, and a weather conceptual model of flood-causing rainstorm is constructed. The results shown that during the autumn flood season, single peak flood processes occur most frequently in the upper reaches of the Hanjiang River, and the flood hydrograph has diversity. The bimodal pattern has a large flood volume, high peak, and rapid rise and fall of water level, with a mostly pointed and thin shape. The multi-peak flood has the largest volume and longest duration, with varying peak heights. The duration of the unimodal flood process is short, and the daily accumulated precipitation fluctuates greatly, with rapid peak formation, and all of them are sharp and thin. The duration of the bimodal process is generally no less than 11 d, the interval between rainstorm processes is short, the difference between the main peak and the secondary peak is small, and the peak value is more than 20 000 m3·s-1. The duration of the multi-peak precipitation process is the longest, and in the continuous cloudy and rainy weather can last for more than 20 d, but the main peak value is lower than that of the bimodal pattern. From the perspective of large-scale circulation patterns, in mid to high latitudes, there are generally three more obvious pattern adjustments in the bimodal pattern, with a larger meridional degree of circulation. There are fewer adjustments to the multi-peak circulation pattern, and the southern side of Lake Baikal is mostly characterized by small trough and ridge activities. There is no significant adjustment in the unimodal pattern. In the middle and low latitudes, the western Pacific subtropical high with multiple peaks moves most strongly westward, without typhoon or tropical cyclone activities. The bimodal subtropical high oscillates frequently from east to west, often involving tropical cyclones. The unimodal pattern is often accompanied by the merging of continental and oceanic high-pressure systems, with few activities of typhoons or tropical cyclones. The weather conceptual models of flood-causing rainstorm in the upper reaches of the Hanjiang River during the autumn flood season can be divided into five categories: high trough jet forcing (A-Ⅰ), high trough low vortex shear (A-Ⅲ), subtropical high periphery jet forcing (B-Ⅰ), subtropical high periphery southerly flow weak forcing (B-Ⅱ) and subtropical high interior low vortex shear (C-Ⅲ). Bimodal floods are mostly dominated by pattern A, while multimodal floods are mostly dominated by pattern B, with both single peak pattern A and pattern B appearing, and pattern C is only unique to single peak pattern. In addition, ground pattern Ⅰ and pattern Ⅱ are often combined with A-Ⅰ, A-Ⅲ, B-Ⅰ, etc. When the three-layer weather system is well configured, the probability of flooding will be significantly increased.
2025,51(2):221-228, DOI: 10.7519/j.issn.1000-0526.2024.102601
Abstract:
The atmospheric attenuation characteristics of the FY-3 precipitation measurement radar external calibration test field were analyzed based on sounding data from the National High Altitude Meteorological Observatory in Xilinhot throughout 2023. A quick method for estimating atmospheric attenuation has been established by exploring the relationship between total precipitation water and attenuation. The results indicate that the annual variation of oxygen attenuation is very small, while water vapor attenuation has obvious seasonal characteristics. In addition, the attenuation of water vapor is closely related to the total amount of water vapor. The attenuation of water vapor in Ku-band is numerically equivalent to approximately 1/250 of the total amount of water vapor, and the attenuation of water vapor in Ka-band is approximately 4 times that of the Ku-band. Moreover, there is good consistency between the attenuation estimated by the quick method and the attenuation calculated by the normal method, which indicates that the quick method is reasonable and feasible. The calculation and analysis of atmospheric attenuation could lay a foundation for the smooth implementation of precipitation radar external calibration experiments.
The atmospheric attenuation characteristics of the FY-3 precipitation measurement radar external calibration test field were analyzed based on sounding data from the National High Altitude Meteorological Observatory in Xilinhot throughout 2023. A quick method for estimating atmospheric attenuation has been established by exploring the relationship between total precipitation water and attenuation. The results indicate that the annual variation of oxygen attenuation is very small, while water vapor attenuation has obvious seasonal characteristics. In addition, the attenuation of water vapor is closely related to the total amount of water vapor. The attenuation of water vapor in Ku-band is numerically equivalent to approximately 1/250 of the total amount of water vapor, and the attenuation of water vapor in Ka-band is approximately 4 times that of the Ku-band. Moreover, there is good consistency between the attenuation estimated by the quick method and the attenuation calculated by the normal method, which indicates that the quick method is reasonable and feasible. The calculation and analysis of atmospheric attenuation could lay a foundation for the smooth implementation of precipitation radar external calibration experiments.
2025,51(2):229-238, DOI: 10.7519/j.issn.1000-0526.2024.102901
Abstract:
Waterlogging damage is the main limiting factor for stable and high yield of summer maize in Anhui Province. Soil moisture is a direct indicator of agricultural drought and flood conditions. The current density and accuracy of soil moisture observation stations can not satisfy the requirements of drought and flood monitoring, early warning and assessment. To construct a waterlogging index that can reflect the daily changes of soil moisture for summer maize during the seedling stage, based on daily meteorological data, geographic information, and summer maize disaster data of 20 counties (districts) in the northern part of Anhui Province from 1981 to 2020, this paper uses the daily standardized antecedent precipitation evapotranspiration index (SAPEI) in characterizing soil relative humidity. In addition, combined with the industry standard grades of waterlogging for summer maize, the dominant indicators and auxiliary indexes of waterlogging for summer maize during the seedling stage are established. The verified accuracy of the indexes exceeds 90%. The temporal manifestation of waterlogging during the seedling stage of summer maize in northern Anhui is as follows. The most severe period is from 1991 to 2000 and the period from 2001 to 2010 comes the second. 2003 is the year most serious waterlogging in the past 40 years. In spatial distribution, the frequency of waterlogging in the area along the Huaihe River is higher than that in the area north to the Huaihe River. Strengthening the research on monitoring and early warning technology for maize waterlogging and conducting quantitative assessments of regional waterlogging for maize is of great significance to ensure food security in Anhui Province.
Waterlogging damage is the main limiting factor for stable and high yield of summer maize in Anhui Province. Soil moisture is a direct indicator of agricultural drought and flood conditions. The current density and accuracy of soil moisture observation stations can not satisfy the requirements of drought and flood monitoring, early warning and assessment. To construct a waterlogging index that can reflect the daily changes of soil moisture for summer maize during the seedling stage, based on daily meteorological data, geographic information, and summer maize disaster data of 20 counties (districts) in the northern part of Anhui Province from 1981 to 2020, this paper uses the daily standardized antecedent precipitation evapotranspiration index (SAPEI) in characterizing soil relative humidity. In addition, combined with the industry standard grades of waterlogging for summer maize, the dominant indicators and auxiliary indexes of waterlogging for summer maize during the seedling stage are established. The verified accuracy of the indexes exceeds 90%. The temporal manifestation of waterlogging during the seedling stage of summer maize in northern Anhui is as follows. The most severe period is from 1991 to 2000 and the period from 2001 to 2010 comes the second. 2003 is the year most serious waterlogging in the past 40 years. In spatial distribution, the frequency of waterlogging in the area along the Huaihe River is higher than that in the area north to the Huaihe River. Strengthening the research on monitoring and early warning technology for maize waterlogging and conducting quantitative assessments of regional waterlogging for maize is of great significance to ensure food security in Anhui Province.
2025,51(2):239-248, DOI: 10.7519/j.issn.1000-0526.2024.112601
Abstract:
To effectively utilize the characteristics of atmospheric electric field signals and improve the precision of lightning risk warning, using data from an atmospheric electric field instrument installed on a 500 m-height platform at the Guangzhou Tower within a 20 km (radius) range, this paper analyzes the full day (00:00 BT-24:00 BT) data from 83 days with thunderstorm processes and 123 days with non-thunderstorm processes corresponding to the instrument in 2021 and 2022, and then proposes a lightning risk warning method combining time-frequency domain features and one-dimensional Morpho based on the fusion of enhanced empirical wavelet transform and adaptive Savitzky-Golay (EEWT-ASG). This proposed method uses the spectral width first-order backward difference and mean square error of time-frequency domain features as warning and judgment features for lightning and non-lightning processes, and energy difference is used as a feature for judging the release of warnings. Through selecting samples for effectiveness testing in this article, the proposed lightning risk warning method achieves an accuracy (POD) of 77.11% during thunderstorms, and also has the lowest false alarm ratio (40.00%) and highest critical success index (0.51) performance. Besides, an average warning lead time of 22.27 min is achieved. During non-thunderstorm processes, POD reaches 90.24%. Most warnings have a delay time of 0-40 min, with an average delay time of 32 min. According to the comparison with previous algorithm models, the method proposed in this paper for warning and relief can meet the needs of lightning risk warning in industries with high lightning impact.
To effectively utilize the characteristics of atmospheric electric field signals and improve the precision of lightning risk warning, using data from an atmospheric electric field instrument installed on a 500 m-height platform at the Guangzhou Tower within a 20 km (radius) range, this paper analyzes the full day (00:00 BT-24:00 BT) data from 83 days with thunderstorm processes and 123 days with non-thunderstorm processes corresponding to the instrument in 2021 and 2022, and then proposes a lightning risk warning method combining time-frequency domain features and one-dimensional Morpho based on the fusion of enhanced empirical wavelet transform and adaptive Savitzky-Golay (EEWT-ASG). This proposed method uses the spectral width first-order backward difference and mean square error of time-frequency domain features as warning and judgment features for lightning and non-lightning processes, and energy difference is used as a feature for judging the release of warnings. Through selecting samples for effectiveness testing in this article, the proposed lightning risk warning method achieves an accuracy (POD) of 77.11% during thunderstorms, and also has the lowest false alarm ratio (40.00%) and highest critical success index (0.51) performance. Besides, an average warning lead time of 22.27 min is achieved. During non-thunderstorm processes, POD reaches 90.24%. Most warnings have a delay time of 0-40 min, with an average delay time of 32 min. According to the comparison with previous algorithm models, the method proposed in this paper for warning and relief can meet the needs of lightning risk warning in industries with high lightning impact.
2025,51(2):249-256, DOI: 10.7519/j.issn.1000-0526.2025.011801
Abstract:
The main features of the atmospheric circulation in November 2024 are as follows. The polar vortex in the Northern Hemisphere exhibited a dipole pattern, with the primary center located in the region from north Asia to the area east of Novaya Zemlya, stronger than the long-term average for the same period. The Eurasian mid-to-high latitudes gradually transitioned from a “two ridges and one trough” pattern to a “two troughs and one ridge” pattern. China’s mid-to-high latitudes were controlled by a weak meridional circulation and a high-pressure ridge with fewer upper-level trough activities, resulting in less frequent and weaker cold air processes affecting China, so the national average temperature was significantly higher than normal. The subtropical high was stronger. In November, the national average temperature was 5.2℃, 1.9℃ higher than the long-term average, making it the warmest November since 1961.
The national average precipitation was 21.2 mm,
5% more than that in the same period of normal years. The first cold wave and snowfall weather process occurred in the last dekad of November. Additionally, there were 4 typhoons generated in the Northwest Pacific and the South China Sea in November, 1.8 typhoons more than before. As the result of the static weather condition, there were three fog haze events in November.
The main features of the atmospheric circulation in November 2024 are as follows. The polar vortex in the Northern Hemisphere exhibited a dipole pattern, with the primary center located in the region from north Asia to the area east of Novaya Zemlya, stronger than the long-term average for the same period. The Eurasian mid-to-high latitudes gradually transitioned from a “two ridges and one trough” pattern to a “two troughs and one ridge” pattern. China’s mid-to-high latitudes were controlled by a weak meridional circulation and a high-pressure ridge with fewer upper-level trough activities, resulting in less frequent and weaker cold air processes affecting China, so the national average temperature was significantly higher than normal. The subtropical high was stronger. In November, the national average temperature was 5.2℃, 1.9℃ higher than the long-term average, making it the warmest November since 1961.
The national average precipitation was 21.2 mm,
5% more than that in the same period of normal years. The first cold wave and snowfall weather process occurred in the last dekad of November. Additionally, there were 4 typhoons generated in the Northwest Pacific and the South China Sea in November, 1.8 typhoons more than before. As the result of the static weather condition, there were three fog haze events in November.
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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 20, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.031901
Abstract:
The boundary layer low-level jet plays an important role in the exchange of material and energy, and is closely related to precipitation, air pollution and other issues. Studying the boundary layer low-level jet helps to solve related problems and improve the quality of human life. During the study of the boundary layer low-level jet in Beijing by using the Doppler ladar data from March 2018 to February 2019, a special jet was found. This paper uses numerical simulation method to study the formation mechanism of this phenomenon. The results are as followed. The jet intensity is about 6 m·s-1, mainly from 02:00 to 09:00. 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 direction inside the jet is northeaster wind, while above the jet is southwest wind. The wind direction conversion area is also a weak wind speed area, which wraps the low-level jet, so it is called the weak wind speed zone boundary low-level jet (WBLLJ). Terrain forcing is the root cause of the formation of WBLLJ. Blocked by Taihang Mountains and Yanshan Mountains, under the joint action of night topographic cold discharge, a shallow northeaster wind control zone is formed in the plain area near the mountain, with 130 km length, 10 km width, and 600 m high. 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 will wedge into the bottom of the plain and form 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 to form 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 pollutants and the evolution of urban heat island in Beijing.
The boundary layer low-level jet plays an important role in the exchange of material and energy, and is closely related to precipitation, air pollution and other issues. Studying the boundary layer low-level jet helps to solve related problems and improve the quality of human life. During the study of the boundary layer low-level jet in Beijing by using the Doppler ladar data from March 2018 to February 2019, a special jet was found. This paper uses numerical simulation method to study the formation mechanism of this phenomenon. The results are as followed. The jet intensity is about 6 m·s-1, mainly from 02:00 to 09:00. 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 direction inside the jet is northeaster wind, while above the jet is southwest wind. The wind direction conversion area is also a weak wind speed area, which wraps the low-level jet, so it is called the weak wind speed zone boundary low-level jet (WBLLJ). Terrain forcing is the root cause of the formation of WBLLJ. Blocked by Taihang Mountains and Yanshan Mountains, under the joint action of night topographic cold discharge, a shallow northeaster wind control zone is formed in the plain area near the mountain, with 130 km length, 10 km width, and 600 m high. 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 will wedge into the bottom of the plain and form 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 to form 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 pollutants and the evolution of urban heat island in Beijing.
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 17, 2025 , DOI: 10.7519/j.issn.1000-0526.2024.121701
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The three consecutive La Ni?a events occurred from 2020 to 2023 have been widespread concerned, which also led to various global weather and climate anomalies. By using the tropical cyclone datasets from the National Meteorological Center and the National Hurricane Center of the United States, the findings show that the number of tropical cyclones generated in the Northern Pacific in September 2022 is far more than the historical average over the same period, with the number of tropical cyclones in the Northeast Pacific reached the peak in the past 70 years. Based on the reanalysis datasets, this study analyzed the Dynamic Genesis Potential index and found that the vertical movement in the middle troposphere made a great contribution to the increased amount of tropical cyclones in the Northern Pacific. Further researches show that during the La Ni?a event, the temperature of warm pool in the Northwest Pacific continued to warm, convective activity near the Philippines enhanced and the southwesterlies over Maritime Continent strengthened, the subtropical high over the Northwest Pacific shifted northward. The emergence of low-level cyclonic circulation enhanced the ascending movement of the middle troposphere, which is favorable for the genesis of tropical cyclones. At the same time, the La Ni?a event led to an increase in the meridional temperature gradient over the Northeast Pacific, the meridional Hadley circulation being intensified, thus the upward movement over the middle and low latitudes strengthened. As the subtropical high located in western Mexico moves eastward, the number of active tropical cyclones in the Northeast Pacific increases.
The three consecutive La Ni?a events occurred from 2020 to 2023 have been widespread concerned, which also led to various global weather and climate anomalies. By using the tropical cyclone datasets from the National Meteorological Center and the National Hurricane Center of the United States, the findings show that the number of tropical cyclones generated in the Northern Pacific in September 2022 is far more than the historical average over the same period, with the number of tropical cyclones in the Northeast Pacific reached the peak in the past 70 years. Based on the reanalysis datasets, this study analyzed the Dynamic Genesis Potential index and found that the vertical movement in the middle troposphere made a great contribution to the increased amount of tropical cyclones in the Northern Pacific. Further researches show that during the La Ni?a event, the temperature of warm pool in the Northwest Pacific continued to warm, convective activity near the Philippines enhanced and the southwesterlies over Maritime Continent strengthened, the subtropical high over the Northwest Pacific shifted northward. The emergence of low-level cyclonic circulation enhanced the ascending movement of the middle troposphere, which is favorable for the genesis of tropical cyclones. At the same time, the La Ni?a event led to an increase in the meridional temperature gradient over the Northeast Pacific, the meridional Hadley circulation being intensified, thus the upward movement over the middle and low latitudes strengthened. As the subtropical high located in western Mexico moves eastward, the number of active tropical cyclones in the Northeast Pacific increases.
Available online: March 14, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.031301
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Flood forecasting is an effective non engineering measure to reduce flood losses and enhance resilience.And accurate flood forecasting is one of the key technical challenges in the hydrological field. At present, flood forecasting models based on physical mechanisms still have shortcomings in simulation accuracy and efficiency, while forecasting models constructed using deep learning techniques have experienced rapid development.This study comprehensively reviews the principles and characteristics of deep learning models applied in the field of flood forecasting. It summarizes the progress and problems in the application of deep learning models for quantitative and probabilistic flood forecasting. The study also explores the relevance and application prospects of deep learning models in relation to flood physics models, particularly in the parameterization of physical processes, interpretability studies, and error correction of flood forecasting models. It is believed that deep coupling with physical models is the future development direction of deep learning models, which will be an important development paradigm for the time series prediction of flood, and an important research component for realizing the water resource intelligence in the future. Finally, a few thoughts are given on the difficulties of deep learning in flood forecasting, and corresponding solutions are proposed for the current challenges, in order to better explore the application of deep learning technology in the field of flood forecasting.
Flood forecasting is an effective non engineering measure to reduce flood losses and enhance resilience.And accurate flood forecasting is one of the key technical challenges in the hydrological field. At present, flood forecasting models based on physical mechanisms still have shortcomings in simulation accuracy and efficiency, while forecasting models constructed using deep learning techniques have experienced rapid development.This study comprehensively reviews the principles and characteristics of deep learning models applied in the field of flood forecasting. It summarizes the progress and problems in the application of deep learning models for quantitative and probabilistic flood forecasting. The study also explores the relevance and application prospects of deep learning models in relation to flood physics models, particularly in the parameterization of physical processes, interpretability studies, and error correction of flood forecasting models. It is believed that deep coupling with physical models is the future development direction of deep learning models, which will be an important development paradigm for the time series prediction of flood, and an important research component for realizing the water resource intelligence in the future. Finally, a few thoughts are given on the difficulties of deep learning in flood forecasting, and corresponding solutions are proposed for the current challenges, in order to better explore the application of deep learning technology in the field of flood forecasting.
Available online: March 14, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.012301
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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 28, 2025 , DOI: 10.7519/j.issn.1000-0526.2024.121601
Abstract:
The primary source of the bias of Atmospheric Motion Vectors (AMVs) is related to inaccuracies in assigning heights.. The cloud top height algorithm employed by China‘s new generation geostationary meteorological satellite FY-4 series make use of both the infrared window channel and CO2 slicing channel. This leads to an improvement in its accuracy. In this study, cloud top height has been used to correct AMVs of FY-4A through spatiotemporal matching between and the two products. Representative pixels within the AMVs tracking box are searched, and their average cloud top pressure is used to replace the original cloud pressure of the AMVs, achieving height reassignment. Verification using ERA5 reanalysis data shows that after height reassignment, the root mean square error (RMSE) of FY-4A infrared channel AMVs is significantly reduced across high, middle, and low levels. Specifically, the RMSE for the high level decreased from 4.06 m·s?1 to 3.25 m·s?1, for the middle level from 4.25 m·s?1 to 3.71 m·s?1, and for the low level from 2.42 m·s?1 to 2.13 m·s?1. Height reassignment alleviates the problem of AMVs being assigned to overly high altitudes, reducing biases, particularly improving slow motion biases. Case studies of the Northeast Cold Vortex and Typhoon "Chaba" demonstrate that this method can improve the consistency between cloud-derived winds and the background field. Promising applications in numerical weather prediction assimilation and weather process analysis are envisioned.
The primary source of the bias of Atmospheric Motion Vectors (AMVs) is related to inaccuracies in assigning heights.. The cloud top height algorithm employed by China‘s new generation geostationary meteorological satellite FY-4 series make use of both the infrared window channel and CO2 slicing channel. This leads to an improvement in its accuracy. In this study, cloud top height has been used to correct AMVs of FY-4A through spatiotemporal matching between and the two products. Representative pixels within the AMVs tracking box are searched, and their average cloud top pressure is used to replace the original cloud pressure of the AMVs, achieving height reassignment. Verification using ERA5 reanalysis data shows that after height reassignment, the root mean square error (RMSE) of FY-4A infrared channel AMVs is significantly reduced across high, middle, and low levels. Specifically, the RMSE for the high level decreased from 4.06 m·s?1 to 3.25 m·s?1, for the middle level from 4.25 m·s?1 to 3.71 m·s?1, and for the low level from 2.42 m·s?1 to 2.13 m·s?1. Height reassignment alleviates the problem of AMVs being assigned to overly high altitudes, reducing biases, particularly improving slow motion biases. Case studies of the Northeast Cold Vortex and Typhoon "Chaba" demonstrate that this method can improve the consistency between cloud-derived winds and the background field. Promising applications in numerical weather prediction assimilation and weather process analysis are envisioned.
Available online: February 26, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.010202
Abstract:
The continuous heavy rainfall during the Meiyu season in 2020 (May 29 to July 17) led to event since the construction of the Xinanjiang Reservoir and the first time that all the sluices were fully opened. Refined precipitation forecasts are of great support to flood control efforts in the basin. Based on observed precipitation data from various stations, this study examines the forecast performance of four global models and five regional models regarding both overall precipitation patterns and area-specific rainfall within Xin"an River Basin. Additionally, it focuses on evaluating the predictive capabilities of these models regarding extreme and cumulative precipitation effects in the basin to determine whether they can meet the demand of reservoir flood discharge forecasting service. Furthermore, an analysis is conducted to assess how topographic height influences each model"s precipitation forecasts. The results show that: (1) The global model consistently yielded lower precipitation forecast results compared to the regional model. The regional model exhibited high accuracy but had relatively large variability among its predictions. The regional multi-model ensemble average demonstrated superior forecast performance than single model results. (2) The regional model performed well in forecasting rainfall ranging from rainstorm to heavy rainstorm; however, there were some discrepancies in predicting the magnitude and timing of heavy rainstorms. (3) Compare to forecast evaluation of single-day precipitation in models it is more instructive to comprehensively consider the cumulative effects and extreme of precipitation predicted by the models. (4) Topographic height significantly influences extreme rainfall prediction for heavy rainfall events and above. As topographic height increases, the advantage of using a regional model becomes evident while the predictive ability of a global model for heavy rainfall events decreases. Especially for ZJWARMS and ZJWARRS, the TS score has increased from below 0.1 to approximately 0.15. Additionally, moderate or lighter intensity rains do not exhibit significant prediction effects.
The continuous heavy rainfall during the Meiyu season in 2020 (May 29 to July 17) led to event since the construction of the Xinanjiang Reservoir and the first time that all the sluices were fully opened. Refined precipitation forecasts are of great support to flood control efforts in the basin. Based on observed precipitation data from various stations, this study examines the forecast performance of four global models and five regional models regarding both overall precipitation patterns and area-specific rainfall within Xin"an River Basin. Additionally, it focuses on evaluating the predictive capabilities of these models regarding extreme and cumulative precipitation effects in the basin to determine whether they can meet the demand of reservoir flood discharge forecasting service. Furthermore, an analysis is conducted to assess how topographic height influences each model"s precipitation forecasts. The results show that: (1) The global model consistently yielded lower precipitation forecast results compared to the regional model. The regional model exhibited high accuracy but had relatively large variability among its predictions. The regional multi-model ensemble average demonstrated superior forecast performance than single model results. (2) The regional model performed well in forecasting rainfall ranging from rainstorm to heavy rainstorm; however, there were some discrepancies in predicting the magnitude and timing of heavy rainstorms. (3) Compare to forecast evaluation of single-day precipitation in models it is more instructive to comprehensively consider the cumulative effects and extreme of precipitation predicted by the models. (4) Topographic height significantly influences extreme rainfall prediction for heavy rainfall events and above. As topographic height increases, the advantage of using a regional model becomes evident while the predictive ability of a global model for heavy rainfall events decreases. Especially for ZJWARMS and ZJWARRS, the TS score has increased from below 0.1 to approximately 0.15. Additionally, moderate or lighter intensity rains do not exhibit significant prediction effects.
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 19, 2025 , DOI: 10.7519/j.issn.1000-0526.2024.122703
Abstract:
Based on the observation data of Guyuan C-band Doppler weather radar and X-band dual polarization radar, combined with ERA5 hourly reanalysis, Himawari-8 satellite, automatic weather station and conventional observation data, the causation and radar observation characteristics of a local outsize hail (diameter ≥ 5 cm) event which occurred in Liupan Moutains area of Ningxia on 12 July 2021 is analyzed. The results show that: (1) The supercell storm formed by the merger and development of multicell storm caused the occurrence of outsize hail. The mesoscale ground convergence line, mesoscale cyclone and local circulation in Liupan Moutains area were the main triggering and enhancing systems of mesoscale convective systems (MCS), and also affected the movement direction of MCS. (2) When the large hail occured, the C-band radar composite reflectivity (Z) ≥ 65 dBZ, three-body scatter spike (TBSS) length ≥ 20 km, vertically integrated liquid water content (VIL) ≥ 40 kg·m-2. The cross-correlation coefficient (CC) in the high-value area 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 to high layer ZH high-value area were negative and CC ＜ 0.8. (3) When the outsize hail occured, Z ≥ 70 dBZ, TBSS length ≥ 30 km, VIL ≥ 50 kg·m-2 for the C-band radar. CC in the low layer ZH high-value area of the X-band radar was less than 0.6 and the "hole" formed in the area with CC ＜ 0.5 helped to identify the area and altitude of outsize hail in the air. (4) 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. ZH and dual polarization parameter characteristics had good indicative significance for the identification and warning of different hail sizes.
Based on the observation data of Guyuan C-band Doppler weather radar and X-band dual polarization radar, combined with ERA5 hourly reanalysis, Himawari-8 satellite, automatic weather station and conventional observation data, the causation and radar observation characteristics of a local outsize hail (diameter ≥ 5 cm) event which occurred in Liupan Moutains area of Ningxia on 12 July 2021 is analyzed. The results show that: (1) The supercell storm formed by the merger and development of multicell storm caused the occurrence of outsize hail. The mesoscale ground convergence line, mesoscale cyclone and local circulation in Liupan Moutains area were the main triggering and enhancing systems of mesoscale convective systems (MCS), and also affected the movement direction of MCS. (2) When the large hail occured, the C-band radar composite reflectivity (Z) ≥ 65 dBZ, three-body scatter spike (TBSS) length ≥ 20 km, vertically integrated liquid water content (VIL) ≥ 40 kg·m-2. The cross-correlation coefficient (CC) in the high-value area 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 to high layer ZH high-value area were negative and CC ＜ 0.8. (3) When the outsize hail occured, Z ≥ 70 dBZ, TBSS length ≥ 30 km, VIL ≥ 50 kg·m-2 for the C-band radar. CC in the low layer ZH high-value area of the X-band radar was less than 0.6 and the "hole" formed in the area with CC ＜ 0.5 helped to identify the area and altitude of outsize hail in the air. (4) 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. ZH and dual polarization parameter characteristics had good indicative significance for the identification and warning of different hail sizes.
Available online: February 18, 2025 , 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 model forecast field data of CMA-GFS, a comparative analysis and evaluation of the observation data of the two radiosondes on each mandatory level were conducted. The results show that the GTS12 radiosonde and GTS1 radiosonde have good consistency in temperature and geopotential height observation data, the absolute value of bias of temperature and geopotential height are less than 0.5 ℃ and 30.0 gpm except for a few mandatory levels. The relative humidity observation data of GTS12 radiosonde is about4.6 % larger than that of GTS1 radiosonde. 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 of the GTS12 radiosonde are significantly better than those of the GTS1 radiosonde, but the relative humidity is slightly worse than that of the GTS1 radiosonde. The absolute average bias of temperature observed by GTS12 radiosonde and GTS1 radiosonde relative to the CMA-GFS model data is about 0.34 ℃ and 0.44 ℃, respectively. The average root mean square error is about 1.23 ℃ and 1.31 ℃, and the average related coefficient is about 0.908 and 0.916, respectively. The corresponding of geopotential heights are 11.05 gpm and 14.97 gpm, 18.76 gpm and 25.16 gpm, 0.948 and 0.934. The corresponding of relative humidity are 5.26% and 8.59%, 16.19% and 18.44%, 0.687 and 0.627. indicating that the consistency between the observation data of the GTS12 radiosonde and the CMA-GFS model data is better than that of the GTS1 radiosonde.
Based on the parallel observation data of GTS12 and GTS1 radiosondes from 89 high altitude meteorological observation stations in China and the model forecast field data of CMA-GFS, a comparative analysis and evaluation of the observation data of the two radiosondes on each mandatory level were conducted. The results show that the GTS12 radiosonde and GTS1 radiosonde have good consistency in temperature and geopotential height observation data, the absolute value of bias of temperature and geopotential height are less than 0.5 ℃ and 30.0 gpm except for a few mandatory levels. The relative humidity observation data of GTS12 radiosonde is about4.6 % larger than that of GTS1 radiosonde. 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 of the GTS12 radiosonde are significantly better than those of the GTS1 radiosonde, but the relative humidity is slightly worse than that of the GTS1 radiosonde. The absolute average bias of temperature observed by GTS12 radiosonde and GTS1 radiosonde relative to the CMA-GFS model data is about 0.34 ℃ and 0.44 ℃, respectively. The average root mean square error is about 1.23 ℃ and 1.31 ℃, and the average related coefficient is about 0.908 and 0.916, respectively. The corresponding of geopotential heights are 11.05 gpm and 14.97 gpm, 18.76 gpm and 25.16 gpm, 0.948 and 0.934. The corresponding of relative humidity are 5.26% and 8.59%, 16.19% and 18.44%, 0.687 and 0.627. indicating that the consistency between the observation data of the GTS12 radiosonde and the CMA-GFS model data is better than that of the GTS1 radiosonde.
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 13, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.011501
Abstract:
During May 21 to June 21 in 2022, the strongest dragon-boat precipitation process in the last decade occurred in South China. The extreme dragon-boat precipitation process, with a large cumulative rainfall and frequent heavy rainfall processes, caused significant economic losses. In this paper, two operational models, TRAMS and ECMWF, which are commonly used by forecasters in South China, are selected to divide the torrential rain during dragon-boat precipitation into front-zone torrential rain and warm-sector torrential rain, and are verified and evaluated, in order 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 position prediction of torrential rain by TRAMS mostly has a eastward bias, while ECMWF has a northward bias. The deviations in precipitation position are closely related to the differences in the forecast bias of the two models for low-level southwesterly flow. The area prediction of the front-zone torrential rain by TRAMS is close to the observation, while the forecast area of warm-sector torrential rain is large. The forecast areas of ECMWF for both front-zone torrential rain and warm-sector torrential rain are small. 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 reference value for model developers to further carry out research on error source diagnosis and technical improvement of TRAMS.
During May 21 to June 21 in 2022, the strongest dragon-boat precipitation process in the last decade occurred in South China. The extreme dragon-boat precipitation process, with a large cumulative rainfall and frequent heavy rainfall processes, caused significant economic losses. In this paper, two operational models, TRAMS and ECMWF, which are commonly used by forecasters in South China, are selected to divide the torrential rain during dragon-boat precipitation into front-zone torrential rain and warm-sector torrential rain, and are verified and evaluated, in order 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 position prediction of torrential rain by TRAMS mostly has a eastward bias, while ECMWF has a northward bias. The deviations in precipitation position are closely related to the differences in the forecast bias of the two models for low-level southwesterly flow. The area prediction of the front-zone torrential rain by TRAMS is close to the observation, while the forecast area of warm-sector torrential rain is large. The forecast areas of ECMWF for both front-zone torrential rain and warm-sector torrential rain are small. 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 reference value for model developers to further carry out research on error source diagnosis and technical improvement of TRAMS.
Available online: February 10, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.012001
Abstract:
To improve the accuracy of precipitation nowcasting, this paper proposes an adversarial neural network model named CastNet that combines deep neural networks. This model utilizes the Recurrent Neural Network (RNN) to capture the spatio-temporal features of radar echo data, employs the Adversarial Neural Network (GAN) to simulate the generation and dissipation changes of cloud clusters, and then integrates the optical flow constraint into the neural network to guide the model training, which accelerates the learning process of the neural network and enhances the spatio-temporal consistency of the model, effectively solving the problem of forecast ambiguity and significantly improving the accuracy of precipitation intensity and location. Tests were conducted on 9 major precipitation processes in Guangxi and its surrounding areas (104.41° - 112.08°E, 20.9° - 26.49°N) from May to October 2023. The results show that under various precipitation intensities (≥0.1, ≥2, ≥7, ≥15, ≥25 and≥40 mmh?1), the average TS scores of SWAN 2.0 are 0.458, 0.27, 0.085, 0.034, 0.014 and 0.003 respectively; the average TS scores of SWAN 3.0 are 0.452, 0.402, 0.225, 0.129, 0.085 and 0.048 respectively; and the average TS scores of the CastNet model are 0.439, 0.397, 0.225, 0.139, 0.104 and 0.073 respectively. Its scores are higher than those of SWAN 2.0 and SWAN 3.0 under high-intensity precipitation of ≥7 mmh?1 and above. In addition, as the forecast lead time extends, the relative advantage of CastNet becomes more obvious.
To improve the accuracy of precipitation nowcasting, this paper proposes an adversarial neural network model named CastNet that combines deep neural networks. This model utilizes the Recurrent Neural Network (RNN) to capture the spatio-temporal features of radar echo data, employs the Adversarial Neural Network (GAN) to simulate the generation and dissipation changes of cloud clusters, and then integrates the optical flow constraint into the neural network to guide the model training, which accelerates the learning process of the neural network and enhances the spatio-temporal consistency of the model, effectively solving the problem of forecast ambiguity and significantly improving the accuracy of precipitation intensity and location. Tests were conducted on 9 major precipitation processes in Guangxi and its surrounding areas (104.41° - 112.08°E, 20.9° - 26.49°N) from May to October 2023. The results show that under various precipitation intensities (≥0.1, ≥2, ≥7, ≥15, ≥25 and≥40 mmh?1), the average TS scores of SWAN 2.0 are 0.458, 0.27, 0.085, 0.034, 0.014 and 0.003 respectively; the average TS scores of SWAN 3.0 are 0.452, 0.402, 0.225, 0.129, 0.085 and 0.048 respectively; and the average TS scores of the CastNet model are 0.439, 0.397, 0.225, 0.139, 0.104 and 0.073 respectively. Its scores are higher than those of SWAN 2.0 and SWAN 3.0 under high-intensity precipitation of ≥7 mmh?1 and above. In addition, as the forecast lead time extends, the relative advantage of CastNet becomes more obvious.
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: February 08, 2025 , DOI: 10.7519/j.issn.1000-0526.2024.122702
Abstract:
Based on the precipitation data from automatic weather stations and ERA5 reanalysis data, case seletion and classification of synoptic circulation are carried on for warm-sector heavy rainfall of the first rainy season in Huizhou from April to June 2003 to 2021. And a comparison is used to study the characteristics of mean synoptic circulation and environmental parameters between different types of warm-sector rainfall events. The results showed that there are a total of 47 warm-sector heavy rainfall events in Huizhou during the first rainy season. Accroding to synoptic circulation, the selected warm-sector rainfall events are divided into three types, i.e., shear line (the first type), shortwave trough low level jet (the second type), and the edge of subtropical high the entrance of low level jet(the third type). A further comparison of mean synoptic circulation between different types of warm-sector rainfall events show that Huizhou is under the control of the west wind flow and the southwest flow around the subtropical high at 500hPa, except for the second type of heavy rainfall. In low-level, there are double low-level jet(southwest low-level jet and boundary layer low-level jet) near Huizhou both in the second and third type of heavy rainfall, while in the first type of heavy rain, boundary layer low-level jet just occurred in the south of the Pearl River Estuary at 925hPa. Finally, the analysis of environmental parameters indicate that in terms of average, the first type of heavy rainfall is superior to other types of heavy rainfall in vertical wind shear; the second type of heavy rainfall is superior to other types of heavy rainfall in the depression of dew point at 850hPa、atmospheric precipitable water、convective available potential energy and K index; the third type of heavy rainfall is superior to other types of heavy rainfall in the maximum southerly wind speed below 850hPa.
Based on the precipitation data from automatic weather stations and ERA5 reanalysis data, case seletion and classification of synoptic circulation are carried on for warm-sector heavy rainfall of the first rainy season in Huizhou from April to June 2003 to 2021. And a comparison is used to study the characteristics of mean synoptic circulation and environmental parameters between different types of warm-sector rainfall events. The results showed that there are a total of 47 warm-sector heavy rainfall events in Huizhou during the first rainy season. Accroding to synoptic circulation, the selected warm-sector rainfall events are divided into three types, i.e., shear line (the first type), shortwave trough low level jet (the second type), and the edge of subtropical high the entrance of low level jet(the third type). A further comparison of mean synoptic circulation between different types of warm-sector rainfall events show that Huizhou is under the control of the west wind flow and the southwest flow around the subtropical high at 500hPa, except for the second type of heavy rainfall. In low-level, there are double low-level jet(southwest low-level jet and boundary layer low-level jet) near Huizhou both in the second and third type of heavy rainfall, while in the first type of heavy rain, boundary layer low-level jet just occurred in the south of the Pearl River Estuary at 925hPa. Finally, the analysis of environmental parameters indicate that in terms of average, the first type of heavy rainfall is superior to other types of heavy rainfall in vertical wind shear; the second type of heavy rainfall is superior to other types of heavy rainfall in the depression of dew point at 850hPa、atmospheric precipitable water、convective available potential energy and K index; the third type of heavy rainfall is superior to other types of heavy rainfall in the maximum southerly wind speed below 850hPa.
Available online: January 17, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.010801
Abstract:
Liquid Water Content (LWC), Median Volume Diameter (MVD), Outside Air Temperature (OAT) and other meteorological conditions are important meteorological factors affecting the intensity of aircraft icing, and are also the basic condition for measuring and evaluating whether the aircraft natural icing test flight meets the airworthiness standard. The meteorological conditions of a domestic large passenger aircraft"s natural icing test flight on January 22, 2022 were analyzed using multi-source meteorological data. The results show that the high-altitude weather background of this natural icing forensic test flight is a latitudinal fluctuating airflow, and the near-surface layer cooperates with the cold air inversion, forcing the southwest warm and humid airflow in the middle and lower layers of the troposphere to lift northward, and forming a wide range of non-precipitation layered cloud system. The height of the cloud top in the test area developed from 3.0 km to 4.6 km, and an inversion layer existed in 1.3-3.5 km, with the lowest temperature at the cloud top of -14 ℃, no precipitation in the cloud, and the radar basic reflectivity＜15 dBz. The ambient temperature of the two times of penetrating the cloud and the standby flight in the cloud for 45 min hovering flights was -10～-7 ℃, the relative humidity＞80%, and the scattering of water vapor flux＜-2.7×10-7 g/(s?hPa?cm2), providing ideal temperature and water vapor conditions for the natural icing test flights, and a weak updraft of -0.2 Pa?s-1 in the middle and upper part of the cloud layer, which contributes to the growth of the supercooled cloud droplets. The DMT sounding data show that the supercooled cloud is inhomogeneous both vertically and horizontally, and that supercooled cloud droplets predominate inside the cloud, and the average LWC value is 0.23-0.27 g?m-3, and the mean value of MVD is 15.82-15.93 μm. There are natural aircraft ice meteorological conditions in winter under the influence of the "inversion + inversion trough" weather system, which is conducive to carrying out aircraft natural icing forensic tests in Shaanxi.
Liquid Water Content (LWC), Median Volume Diameter (MVD), Outside Air Temperature (OAT) and other meteorological conditions are important meteorological factors affecting the intensity of aircraft icing, and are also the basic condition for measuring and evaluating whether the aircraft natural icing test flight meets the airworthiness standard. The meteorological conditions of a domestic large passenger aircraft"s natural icing test flight on January 22, 2022 were analyzed using multi-source meteorological data. The results show that the high-altitude weather background of this natural icing forensic test flight is a latitudinal fluctuating airflow, and the near-surface layer cooperates with the cold air inversion, forcing the southwest warm and humid airflow in the middle and lower layers of the troposphere to lift northward, and forming a wide range of non-precipitation layered cloud system. The height of the cloud top in the test area developed from 3.0 km to 4.6 km, and an inversion layer existed in 1.3-3.5 km, with the lowest temperature at the cloud top of -14 ℃, no precipitation in the cloud, and the radar basic reflectivity＜15 dBz. The ambient temperature of the two times of penetrating the cloud and the standby flight in the cloud for 45 min hovering flights was -10～-7 ℃, the relative humidity＞80%, and the scattering of water vapor flux＜-2.7×10-7 g/(s?hPa?cm2), providing ideal temperature and water vapor conditions for the natural icing test flights, and a weak updraft of -0.2 Pa?s-1 in the middle and upper part of the cloud layer, which contributes to the growth of the supercooled cloud droplets. The DMT sounding data show that the supercooled cloud is inhomogeneous both vertically and horizontally, and that supercooled cloud droplets predominate inside the cloud, and the average LWC value is 0.23-0.27 g?m-3, and the mean value of MVD is 15.82-15.93 μm. There are natural aircraft ice meteorological conditions in winter under the influence of the "inversion + inversion trough" weather system, which is conducive to carrying out aircraft natural icing forensic tests in Shaanxi.
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.1000-0526.2024.111401
Abstract:
To address the issue of high-concealed abnormal wind directions in automatic weather station (AWS) data，this study establish an abnormal wind direction identification method based on the Density-Based Spatial Clustering of Applications with Noise (DBSCAN) clustering algorithm. Historical wind direction data from 16 weather events affecting Guangzhou between 2016 and 2022, including cold waves, cold air masses, and typhoons, as well as real-time wind direction data from AWSs during the impact of Typhoon Sura (No. 2309), were used to detect abnormal wind directions. The analysis results reveal that the proportion of AWSs with suspicious wind directions in historical cases ranges from 0.46% to 5.56%, while the proportion of AWSs with erroneous wind directions ranges from 0.25% to 2.05%.During the real-time case of Typhoon Sura,the method identified 13 AWSs with significantly deviating wind directions from the dominant ground wind direction, primarily due to wind direction sensor malfunctions and environmental impacts on AWS observations. Compared to the traditional method, the accuracy of wind direction error identification has improved by 20.32%.The new method provides a novel approach for the quality control of historical wind direction data from AWSs and offers an effective reference for the operational monitoring and on-site verification of AWS equipment.
To address the issue of high-concealed abnormal wind directions in automatic weather station (AWS) data，this study establish an abnormal wind direction identification method based on the Density-Based Spatial Clustering of Applications with Noise (DBSCAN) clustering algorithm. Historical wind direction data from 16 weather events affecting Guangzhou between 2016 and 2022, including cold waves, cold air masses, and typhoons, as well as real-time wind direction data from AWSs during the impact of Typhoon Sura (No. 2309), were used to detect abnormal wind directions. The analysis results reveal that the proportion of AWSs with suspicious wind directions in historical cases ranges from 0.46% to 5.56%, while the proportion of AWSs with erroneous wind directions ranges from 0.25% to 2.05%.During the real-time case of Typhoon Sura,the method identified 13 AWSs with significantly deviating wind directions from the dominant ground wind direction, primarily due to wind direction sensor malfunctions and environmental impacts on AWS observations. Compared to the traditional method, the accuracy of wind direction error identification has improved by 20.32%.The new method provides a novel approach for the quality control of historical wind direction data from AWSs and offers an effective reference for the operational monitoring and on-site verification of AWS equipment.
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: January 03, 2025 , DOI: 10.7519/j.issn.1000-0526.2025.010201
Abstract:
According to the specific image feature that the bird echo shows obvious ring shape on the Weather Radar reflectivity product, an improved algorithm based on a lightweight convolutional neural network You Only Look Once Version5（YOLOv5） and multi-object tracking based on Deep learning based Simple Online and Realtime Tracking（DeepSort） is proposed to identify ,the?training?and?test?datasets?are?constructed?fromradar?volumetric?scanning?echo?intensity data?obtained?from?the?Yingkou Weather?Radar?from?2020?to?2023, track the bird echo respectively. Firstly, Shuffle Attention（SA）, a lightweight attention mechanism, is introduced into YOLOv5 algorithm to improve the accuracy and effectiveness of the overall model detection. Secondly, in DeepSort algorithm, the original cross merge ratio Intersection over Union（IOU） matching mechanism is replaced by an improved the loss function of object detection Distance-Intersection over Union（DIOU） matching mechanism. DIoU introduces the distance between the center points of the boundary box on the basis of calculating the overlap degree of the boundary box, so as to provide more accurate positioning. The number of identification （ID） error matching and ID switching caused by partial occlusion overlap is reduced. The experimental results show that the optimized YOLOv5 algorithm improves the accuracy by 2.6%, the recall rate by 1%, and the average accuracy of threshold values greater than 0.5 by 1.2%. The improved DeepSort algorithm reduces the number of ID switches by 2 times, multi target tracking accuracy Multi-Object Tracking Accuracy（MOTA） increases by 4.5%, the improved lightweight of the initial model, and the overall detection performance is significantly improved, meeting the actual demand for bird echo recognition and tracking.
According to the specific image feature that the bird echo shows obvious ring shape on the Weather Radar reflectivity product, an improved algorithm based on a lightweight convolutional neural network You Only Look Once Version5（YOLOv5） and multi-object tracking based on Deep learning based Simple Online and Realtime Tracking（DeepSort） is proposed to identify ,the?training?and?test?datasets?are?constructed?fromradar?volumetric?scanning?echo?intensity data?obtained?from?the?Yingkou Weather?Radar?from?2020?to?2023, track the bird echo respectively. Firstly, Shuffle Attention（SA）, a lightweight attention mechanism, is introduced into YOLOv5 algorithm to improve the accuracy and effectiveness of the overall model detection. Secondly, in DeepSort algorithm, the original cross merge ratio Intersection over Union（IOU） matching mechanism is replaced by an improved the loss function of object detection Distance-Intersection over Union（DIOU） matching mechanism. DIoU introduces the distance between the center points of the boundary box on the basis of calculating the overlap degree of the boundary box, so as to provide more accurate positioning. The number of identification （ID） error matching and ID switching caused by partial occlusion overlap is reduced. The experimental results show that the optimized YOLOv5 algorithm improves the accuracy by 2.6%, the recall rate by 1%, and the average accuracy of threshold values greater than 0.5 by 1.2%. The improved DeepSort algorithm reduces the number of ID switches by 2 times, multi target tracking accuracy Multi-Object Tracking Accuracy（MOTA） increases by 4.5%, the improved lightweight of the initial model, and the overall detection performance is significantly improved, meeting the actual demand for bird echo recognition and tracking.
Available online: December 26, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.111801
Abstract:
Doppler spectral 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 study used the difference between short-pulse and long-pulse modes to determine the cloud signal boundary for the first time. The ‘ghost echo’ was removed and the cloud signal boundary was used to calculated the noise level, forming a new denoising method. In addition, the sensitivity of cloud signal boundary changing with the difference threshold T was analyzed. Based on the small particle tracer method, the left cloud signal boundary after denoising was used to calculate the vertical air velocity. Two rainfall (snow) cases in Beijing were analyzed and compared with the in-situ aircraft observation results of the vertical air velocity. It was verified that the new denoising method can effectively remove the ‘ghost echo’. Although a certain percentage deviation existed between the average vertical air velocity obtained by cloud radar and aircraft. The direction and magnitude corresponded well in general. This method and the retrieved results were reasonable.
Doppler spectral 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 study used the difference between short-pulse and long-pulse modes to determine the cloud signal boundary for the first time. The ‘ghost echo’ was removed and the cloud signal boundary was used to calculated the noise level, forming a new denoising method. In addition, the sensitivity of cloud signal boundary changing with the difference threshold T was analyzed. Based on the small particle tracer method, the left cloud signal boundary after denoising was used to calculate the vertical air velocity. Two rainfall (snow) cases in Beijing were analyzed and compared with the in-situ aircraft observation results of the vertical air velocity. It was verified that the new denoising method can effectively remove the ‘ghost echo’. Although a certain percentage deviation existed between the average vertical air velocity obtained by cloud radar and aircraft. The direction and magnitude corresponded well in general. This method and the retrieved results were reasonable.
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.
Available online: June 20, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.022003
Abstract:
Based on forecast products of the European Center for Medium-Range Weather Forecasts - Integrated Forecasting System(ECMWF-IFS) and hourly temperature observation data from the China Meteorological Administration Land Data Assimilation System(CLDAS), an enhanced model named ED-LSTM-FCNN is constructed, incorporating an embedding layer module to handle high-dimensional spatial and temporal features. A fully connected neural network was utilized to integrate various features types and achieve regression prediction of temperature, generating gridded hourly temperature forecast products with a resolution of 0.05°×0.05°. Verification for the 2022 forecast in Hunan Province revealed that the model exhibits a notable capacity to mitigate forecast errors inherent in the numerical model, thereby enhancing the overall forecast stability. The root mean square errors (RMSE) for forecast lead times ranging from 1 to 24 hours exhibit a reduction of 25.4% to 37.7% when compared to ECMWF-IFS and a decrease of 15.8% to 40.0% in comparison to the SCMOC. The model significantly enhances the forecast performance of ECMWF-IFS in spatial prediction, particularly in regions characterized by intricate terrain features. The RMSEs across most areas vary within the range of 1.2 ℃ to 1.6 ℃. The forecast accuracy of the model, with an error margin of ±2 ℃, surpasses 85.0% across various seasons, demonstrating a significant improvement compared to both ECMWF-IFS and SCMOC. The forecasting performance is notably superior, particularly in stable extreme high-temperature weather conditions, when compared to alternative products. In conclusion, this method proved to be effective for high-resolution temperature grid forecasting operations.
Based on forecast products of the European Center for Medium-Range Weather Forecasts - Integrated Forecasting System(ECMWF-IFS) and hourly temperature observation data from the China Meteorological Administration Land Data Assimilation System(CLDAS), an enhanced model named ED-LSTM-FCNN is constructed, incorporating an embedding layer module to handle high-dimensional spatial and temporal features. A fully connected neural network was utilized to integrate various features types and achieve regression prediction of temperature, generating gridded hourly temperature forecast products with a resolution of 0.05°×0.05°. Verification for the 2022 forecast in Hunan Province revealed that the model exhibits a notable capacity to mitigate forecast errors inherent in the numerical model, thereby enhancing the overall forecast stability. The root mean square errors (RMSE) for forecast lead times ranging from 1 to 24 hours exhibit a reduction of 25.4% to 37.7% when compared to ECMWF-IFS and a decrease of 15.8% to 40.0% in comparison to the SCMOC. The model significantly enhances the forecast performance of ECMWF-IFS in spatial prediction, particularly in regions characterized by intricate terrain features. The RMSEs across most areas vary within the range of 1.2 ℃ to 1.6 ℃. The forecast accuracy of the model, with an error margin of ±2 ℃, surpasses 85.0% across various seasons, demonstrating a significant improvement compared to both ECMWF-IFS and SCMOC. The forecasting performance is notably superior, particularly in stable extreme high-temperature weather conditions, when compared to alternative products. In conclusion, this method proved to be effective for high-resolution temperature grid forecasting operations.
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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.
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.
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.
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).
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.
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.
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.
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(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