ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 48,Issue 11,2022 Table of Contents
2022, 48(11):1361-1372.
DOI: 10.7519/j.issn.1000-0526.2022.011502
Abstract:
Deep learning has been developed at an unprecedend speed in radar extrapolation of forecasting, so objective assessment of its applicability is an important prerequisites for operational applications. By utilizing the radar echo open data set of Guangdong-Hong Kong-Macao Greater Bay Area, the performances of 120 min radar echo extrapolation 〖JP2〗by convolutional gated recurrent unit neural network (ConvGRU) and fast dense optical flow (OF) methods based on semi-lagrangian advection scheme have been compared and evaluated based on the echo morphology, probability of detection (POD), false alarm rate (FAR) and threat score (TS). The results show that although the two methods both have effective extrapolation performance, they are not applicable to extrapolate the echo generation, enhancement and locally dispersed.
Deep learning has been developed at an unprecedend speed in radar extrapolation of forecasting, so objective assessment of its applicability is an important prerequisites for operational applications. By utilizing the radar echo open data set of Guangdong-Hong Kong-Macao Greater Bay Area, the performances of 120 min radar echo extrapolation 〖JP2〗by convolutional gated recurrent unit neural network (ConvGRU) and fast dense optical flow (OF) methods based on semi-lagrangian advection scheme have been compared and evaluated based on the echo morphology, probability of detection (POD), false alarm rate (FAR) and threat score (TS). The results show that although the two methods both have effective extrapolation performance, they are not applicable to extrapolate the echo generation, enhancement and locally dispersed.
2022, 48(11):1373-1383.
DOI: 10.7519/j.issn.1000-0526.2022.070101
Abstract:
By using ECMWF-IFS model data and observation data, this study established a fully connected neural network model (DL), tried to make more accurate temperature forecast based on deep learning method for the future 84 hours. The comparative evaluation of ECMWF-IFS and DL was made in 2020. The results show that DL correction can improve the ECMWF-IFS forecasts. The root mean square error (RMSE) of DL in most areas of Hunan is 1.5-2.0℃. There is a significant correction effect for ECMWF-IFS, and the improvement rate increases with the altitude of stations. The diurnal variation is also obvious for the RMSE of ECMWF-IFS/DL model. The RMSE is higher in the afternoon (with higher improvement rate), but lower before sunrise. The improvement rate has different diurnal variation characteristics at different altitudes. DL model shows higher accuracy in the whole year, of which the higher improvement rate appears in October and November (lower in December). In addition, the forecast results in a cold wave process was evaluated. In the accuracy for daily maximum/minimum temperature and the RMSE for 3 h temperature, DL model shows obvious correction ability for the systematic deviation from ECMWF-IFS. The DL temperature curve for single station is much closer to observation than the ECMWF-IFS forecast. Thus, the model can significantly reduce numerical weather prediction error， and its products could basically meet the demands of daily forecast service.
By using ECMWF-IFS model data and observation data, this study established a fully connected neural network model (DL), tried to make more accurate temperature forecast based on deep learning method for the future 84 hours. The comparative evaluation of ECMWF-IFS and DL was made in 2020. The results show that DL correction can improve the ECMWF-IFS forecasts. The root mean square error (RMSE) of DL in most areas of Hunan is 1.5-2.0℃. There is a significant correction effect for ECMWF-IFS, and the improvement rate increases with the altitude of stations. The diurnal variation is also obvious for the RMSE of ECMWF-IFS/DL model. The RMSE is higher in the afternoon (with higher improvement rate), but lower before sunrise. The improvement rate has different diurnal variation characteristics at different altitudes. DL model shows higher accuracy in the whole year, of which the higher improvement rate appears in October and November (lower in December). In addition, the forecast results in a cold wave process was evaluated. In the accuracy for daily maximum/minimum temperature and the RMSE for 3 h temperature, DL model shows obvious correction ability for the systematic deviation from ECMWF-IFS. The DL temperature curve for single station is much closer to observation than the ECMWF-IFS forecast. Thus, the model can significantly reduce numerical weather prediction error， and its products could basically meet the demands of daily forecast service.
2022, 48(11):1384-1401.
DOI: 10.7519/j.issn.1000-0526.2022.042001
Abstract:
In order to reveal the evolution characteristics and effects of low-level jet (LLJ) during the formation of summer rainstorms, comprehensive observational data and reanalysis data are used to compare and analyze the two summer rainstorm cases with different synoptic types and rainstorm intensities in Beijing. The data include the wind profiler radar (WPR)， NCEP/GFS reanalysis data (0.5°×0.5°), and hourly precipitation data from automatic weather stations. The results show that the 16 July rainstorm process in 2018 (shortened as “7·16” rainstorm) was formed under the influence of southwest low-level jet (LLJ) at the edge of the subtropical high. The eastward movement of the vortex and trough, the continuously strengthening of the LLJ, and the influence of terrain convergence line provided extremely favorable conditions including low-level water vapor transport, convergence and uplift conditions for the occurrence of extreme rainstorm. The 22 July rainstorm process in 2019 (shortened as “7·22” rainstorm) was formed under the influence of the LLJ in front of the upper-level trough, which was caused by downward propagation of the upper-level jet during its eastward movement. This kind of LLJ has relatively smaller impacts on water vapor transport and convergence in the lower layers. Within 3 hours before the two rainstorms, similar characteristics appeared as follows: the low-level wind speed increased, the minimum height of LLJ decreased, the LLJ index sharply increased, obvious vertical wind shear occurred below 1500 m, and the vertical wind shear gradually〖JP2〗 increased with the approach of rainstorm. During the “7·16”〖JP〗 rainstorm, the occurrence of the convective cells was triggered by the boundary layer jet (BLJ), and the developing convective system was well organized by the joint action of the LLJ and the terrain convergence line. So, these are the key reasons for the formation of extreme heavy rainfall along the mountains. The characteristic parameters of the LLJ (maximum wind speed of LLJ, minimum height of LLJ, LLJ index) and the magnitude of the vertical wind shear below 1500 m are important indicators for the occurrence of rainstorm.
In order to reveal the evolution characteristics and effects of low-level jet (LLJ) during the formation of summer rainstorms, comprehensive observational data and reanalysis data are used to compare and analyze the two summer rainstorm cases with different synoptic types and rainstorm intensities in Beijing. The data include the wind profiler radar (WPR)， NCEP/GFS reanalysis data (0.5°×0.5°), and hourly precipitation data from automatic weather stations. The results show that the 16 July rainstorm process in 2018 (shortened as “7·16” rainstorm) was formed under the influence of southwest low-level jet (LLJ) at the edge of the subtropical high. The eastward movement of the vortex and trough, the continuously strengthening of the LLJ, and the influence of terrain convergence line provided extremely favorable conditions including low-level water vapor transport, convergence and uplift conditions for the occurrence of extreme rainstorm. The 22 July rainstorm process in 2019 (shortened as “7·22” rainstorm) was formed under the influence of the LLJ in front of the upper-level trough, which was caused by downward propagation of the upper-level jet during its eastward movement. This kind of LLJ has relatively smaller impacts on water vapor transport and convergence in the lower layers. Within 3 hours before the two rainstorms, similar characteristics appeared as follows: the low-level wind speed increased, the minimum height of LLJ decreased, the LLJ index sharply increased, obvious vertical wind shear occurred below 1500 m, and the vertical wind shear gradually〖JP2〗 increased with the approach of rainstorm. During the “7·16”〖JP〗 rainstorm, the occurrence of the convective cells was triggered by the boundary layer jet (BLJ), and the developing convective system was well organized by the joint action of the LLJ and the terrain convergence line. So, these are the key reasons for the formation of extreme heavy rainfall along the mountains. The characteristic parameters of the LLJ (maximum wind speed of LLJ, minimum height of LLJ, LLJ index) and the magnitude of the vertical wind shear below 1500 m are important indicators for the occurrence of rainstorm.
2022, 48(11):1402-1417.
DOI: 10.7519/j.issn.1000-0526.2022.071502
Abstract:
The temporal and spatial distributions of thunderstorm gales in Yunnan are analyzed based on conventional observation data, observed lightning data and significant weather reports from 2011 to 2020. The results are as follows. Thunderstorm gales tend to occur from February to August, characterized by a bimodal pattern, and seen mostly in April. It is easier to see thunderstorm gales in spring than in summer and the daily peaks often appear from 16:00 BT to 17:00 BT. The durations of most thunderstorm gales are 1-4 hours. The high frequency areas are mainly distributed near mountains, including the east of Jade Dragon Snow Mountain, the east of Cangshan Mountain, the Ailao Mountain and the Wuliang Mountain. According to different types of large scale circulation background, three basic synoptic situation configurations of regional thunderstorm gales in Yunnan are proposed, that is, the southern branch trough type, low pressure trough type and quasi-barotropic type. The thunderstorm gale of the southern branch trough type occurs most. The physical parameters are calculated based on NCEP reanalysis data, representing the environmental characteristics such as thermal, dynamical and water vapor conditions, and then the characteristics of physical parameters are analyzed, considering the influence of monthly variation and different backgrounds of atmospheric circulation. The index thresholds of thunderstorm gales are worked out. The results show that the dynamic condition for thunderstorm gale in spring is much better than in summer, and the thermal condition is more significant in summer. The dynamic condition of southern branch trough type or vapor conditions of quasi-barotropic type is better than other weather types. Most meteorological physical parameters tend to increase 6 hours before most thunderstorm gales occur, which indicates that they develop to be more favorable for thunderstorm gale. This finding could provide useful information to the nowcasting and warning of thunderstorm gales.
The temporal and spatial distributions of thunderstorm gales in Yunnan are analyzed based on conventional observation data, observed lightning data and significant weather reports from 2011 to 2020. The results are as follows. Thunderstorm gales tend to occur from February to August, characterized by a bimodal pattern, and seen mostly in April. It is easier to see thunderstorm gales in spring than in summer and the daily peaks often appear from 16:00 BT to 17:00 BT. The durations of most thunderstorm gales are 1-4 hours. The high frequency areas are mainly distributed near mountains, including the east of Jade Dragon Snow Mountain, the east of Cangshan Mountain, the Ailao Mountain and the Wuliang Mountain. According to different types of large scale circulation background, three basic synoptic situation configurations of regional thunderstorm gales in Yunnan are proposed, that is, the southern branch trough type, low pressure trough type and quasi-barotropic type. The thunderstorm gale of the southern branch trough type occurs most. The physical parameters are calculated based on NCEP reanalysis data, representing the environmental characteristics such as thermal, dynamical and water vapor conditions, and then the characteristics of physical parameters are analyzed, considering the influence of monthly variation and different backgrounds of atmospheric circulation. The index thresholds of thunderstorm gales are worked out. The results show that the dynamic condition for thunderstorm gale in spring is much better than in summer, and the thermal condition is more significant in summer. The dynamic condition of southern branch trough type or vapor conditions of quasi-barotropic type is better than other weather types. Most meteorological physical parameters tend to increase 6 hours before most thunderstorm gales occur, which indicates that they develop to be more favorable for thunderstorm gale. This finding could provide useful information to the nowcasting and warning of thunderstorm gales.
CHEN Baofa
,
MA Zhongyuan
,
WANG Lizhi
,
HUANG Longfei
,
LI Yanling
,
SHENG Mengting
,
ZHANG Xiaofang
2022, 48(11):1418-1427.
DOI: 10.7519/j.issn.1000-0526.2022.041002
Abstract:
In order to study the echo characteristics of short-term heavy rainfall in the process of severe rainstorm in Changjiang River Basin, by using the data of weather, radar echo and meteorological, hydrological and rainfall in Changjiang River Basin, as well as the methods of meteorology, statistics, radar meteorology and image processing, this paper studies 10 severe rainstorm processes in Changjiang River Basin from 2000 to 2020. The results show that the severe rainstorm process mainly depends on the short-term heavy rainfall caused by convective activities, including the short-term heavy rainfall and the range of heavy rainfall. When the accumulated rainfall of 3 h is ≥ 100 mm, the red warning of severe rainstorm can be issued in advance. The monitored short-term heavy rainfall accumulated for 3 h at a single monitoring station can be issued earlier to improve the effect of severe rainstorm prediction service. Ultra low-level jet, low-level vortex, high-altitude trough, low-level convergence and high-level divergence play an important role in the process of severe rainstorm in Jingdezhen City. Heavy precipitation is caused by strong echo cell, strong echo short band or other echoes in a wide range of mixed precipitation, and the echo intensity is 45-55 dBz. STI product information can not only reflect the movement information of strong echo, but also analyze the convergence of echo, which has a good reference value for short-term and imminent prediction. On the echo band covering Jiangxi east-west direction, there are many short band echoes in south-north direction, which move from west to east to form “train effect”. The vertical velocity of wind profile radar product can roughly reflect the echo movement. The CR intensity 〖JP2〗causing the torrential rain is mostly〖JP〗 45-50 dBz, the average height of echo top is 12-13 km, the VIL is 5-10 kg·m-2, and the average extension height of strong echo of 45 dBz is 6 km. When the CR intensity is above 45 dBz: the strong echo area reaches Grade 3, and there is a great possibility of short-term heavy precipitation. The strong echo area is in Grade 2, mostly between 20-30 mm·h-1. When the strong echo area is at Grade 1, the precipitation intensity is basically below 20 mm·h-1. These research results could provide a reference basis for understanding, monitoring and early warning the echo characteristics and prediction of short-term heavy rainfall in severe rainstorm in Changjiang River Basin.
In order to study the echo characteristics of short-term heavy rainfall in the process of severe rainstorm in Changjiang River Basin, by using the data of weather, radar echo and meteorological, hydrological and rainfall in Changjiang River Basin, as well as the methods of meteorology, statistics, radar meteorology and image processing, this paper studies 10 severe rainstorm processes in Changjiang River Basin from 2000 to 2020. The results show that the severe rainstorm process mainly depends on the short-term heavy rainfall caused by convective activities, including the short-term heavy rainfall and the range of heavy rainfall. When the accumulated rainfall of 3 h is ≥ 100 mm, the red warning of severe rainstorm can be issued in advance. The monitored short-term heavy rainfall accumulated for 3 h at a single monitoring station can be issued earlier to improve the effect of severe rainstorm prediction service. Ultra low-level jet, low-level vortex, high-altitude trough, low-level convergence and high-level divergence play an important role in the process of severe rainstorm in Jingdezhen City. Heavy precipitation is caused by strong echo cell, strong echo short band or other echoes in a wide range of mixed precipitation, and the echo intensity is 45-55 dBz. STI product information can not only reflect the movement information of strong echo, but also analyze the convergence of echo, which has a good reference value for short-term and imminent prediction. On the echo band covering Jiangxi east-west direction, there are many short band echoes in south-north direction, which move from west to east to form “train effect”. The vertical velocity of wind profile radar product can roughly reflect the echo movement. The CR intensity 〖JP2〗causing the torrential rain is mostly〖JP〗 45-50 dBz, the average height of echo top is 12-13 km, the VIL is 5-10 kg·m-2, and the average extension height of strong echo of 45 dBz is 6 km. When the CR intensity is above 45 dBz: the strong echo area reaches Grade 3, and there is a great possibility of short-term heavy precipitation. The strong echo area is in Grade 2, mostly between 20-30 mm·h-1. When the strong echo area is at Grade 1, the precipitation intensity is basically below 20 mm·h-1. These research results could provide a reference basis for understanding, monitoring and early warning the echo characteristics and prediction of short-term heavy rainfall in severe rainstorm in Changjiang River Basin.
2022, 48(11):1428-1438.
DOI: 10.7519/j.issn.1000-0526.2022.091601
Abstract:
Based on the gauges data of 2423 meteorological stations in China, continuous statistical metrics (correlation coefficient: R, root mean squared error: RMSE, mean absolute error: MAE, relative error: RE) and classified statistical metrics (probability of detection: POD, false alarm ratio: FAR, bias score: Bias, equitable threat score: ETS) are used to analyze the accuracy of Global Prediction Measurement (GPM) precipitation products from three dimensions including different spatial scales, different time scales and different precipitation intensity so as to explore the applicability of GPM satellite precipitation products over mainland China. The main results show that from different spatial scales, GPM precipitation has high observation accuracy in all regions, and the correlation coefficient (R) values of 72% stations exceede 0.7, with the best in East China and relatively poor in Northwest China. RE is concentrated in 0-20%. The accuracy of different altitude-zone elevations show that the overestimation of GPM is more obvious in low altitude (< 2000 m) and high altitude (> 4000 m) regions, and the applicability of GPM data is relatively good in mid-altitude regions (2000-4000 m). In terms of different temporal scales, the total annual precipitation of GPM is consistent with that of rain gauges, and the R is 0.75, but there is a certain deviation in the amount of precipitation, with RMSE being 6.15 mm·d-1. The consistency between GPM precipitation products and rain gauges is better from January to October, with the R above 0.7, slightly lower in November and December. The error value in summer is higher than that in winter, and the RE is positive mostly. In addition, the accuracy results of different precipitation intensity suggests that POD decreases with the increase〖JP2〗 of precipitation intensity. GPM precipitation products have a better detection ability for “moderate rain” intensity, while the detection ability for “light rain” and “heavy rain” is slightly weaker. 〖JP〗
Based on the gauges data of 2423 meteorological stations in China, continuous statistical metrics (correlation coefficient: R, root mean squared error: RMSE, mean absolute error: MAE, relative error: RE) and classified statistical metrics (probability of detection: POD, false alarm ratio: FAR, bias score: Bias, equitable threat score: ETS) are used to analyze the accuracy of Global Prediction Measurement (GPM) precipitation products from three dimensions including different spatial scales, different time scales and different precipitation intensity so as to explore the applicability of GPM satellite precipitation products over mainland China. The main results show that from different spatial scales, GPM precipitation has high observation accuracy in all regions, and the correlation coefficient (R) values of 72% stations exceede 0.7, with the best in East China and relatively poor in Northwest China. RE is concentrated in 0-20%. The accuracy of different altitude-zone elevations show that the overestimation of GPM is more obvious in low altitude (< 2000 m) and high altitude (> 4000 m) regions, and the applicability of GPM data is relatively good in mid-altitude regions (2000-4000 m). In terms of different temporal scales, the total annual precipitation of GPM is consistent with that of rain gauges, and the R is 0.75, but there is a certain deviation in the amount of precipitation, with RMSE being 6.15 mm·d-1. The consistency between GPM precipitation products and rain gauges is better from January to October, with the R above 0.7, slightly lower in November and December. The error value in summer is higher than that in winter, and the RE is positive mostly. In addition, the accuracy results of different precipitation intensity suggests that POD decreases with the increase〖JP2〗 of precipitation intensity. GPM precipitation products have a better detection ability for “moderate rain” intensity, while the detection ability for “light rain” and “heavy rain” is slightly weaker. 〖JP〗
2022, 48(11):1439-1448.
DOI: 10.7519/j.issn.1000-0526.2022.052001
Abstract:
Since the meridional positions of the east and west part of western Pacific subtropical high (WPSH) affect the climate over China differently, we redefined the meridional index of WPSH in this study. The mean latitude of the location of 500 hPa geopotential height maximum along several meridian in 10°-60°N, 110°-130°E and 10°-60°N, 130°-150°E is defined as new west index (Index_NEW_west) and new east index (Index_NEW_east), respectively. Their average value is defined as new meridional index of WPSH (Index_NEW). The correlation between these indices and summer precipitation over eastern China is more significant than the ridge index defined by National Climate Centre (Index_NCC), 〖JP2〗specifically for the positive correlation between Index_NEW_west and precipitation over North China Plain. The negative correlation between Index_NEW_east and precipitation over Yangtze River Basin is similar to that of Index_NCC. Regression of the 500 hPa horizontal wind with respect to Index_NEW_west (Index_NEW_east) presents anticyclonic circulation over western North Pacific and the anticyclone center locates near 38°N, 130°E (40°N, 145°E). The various collocations between north/south anomalies of Index_NEW_west/Index_NEW_east correspond to four types of rainfall patterns. The good relationship between the interannual variation of new indices and summer precipitation over eastern China could provide more valuable references for the study of precipitation prediction and interseasonal movement of rainfall band.
Since the meridional positions of the east and west part of western Pacific subtropical high (WPSH) affect the climate over China differently, we redefined the meridional index of WPSH in this study. The mean latitude of the location of 500 hPa geopotential height maximum along several meridian in 10°-60°N, 110°-130°E and 10°-60°N, 130°-150°E is defined as new west index (Index_NEW_west) and new east index (Index_NEW_east), respectively. Their average value is defined as new meridional index of WPSH (Index_NEW). The correlation between these indices and summer precipitation over eastern China is more significant than the ridge index defined by National Climate Centre (Index_NCC), 〖JP2〗specifically for the positive correlation between Index_NEW_west and precipitation over North China Plain. The negative correlation between Index_NEW_east and precipitation over Yangtze River Basin is similar to that of Index_NCC. Regression of the 500 hPa horizontal wind with respect to Index_NEW_west (Index_NEW_east) presents anticyclonic circulation over western North Pacific and the anticyclone center locates near 38°N, 130°E (40°N, 145°E). The various collocations between north/south anomalies of Index_NEW_west/Index_NEW_east correspond to four types of rainfall patterns. The good relationship between the interannual variation of new indices and summer precipitation over eastern China could provide more valuable references for the study of precipitation prediction and interseasonal movement of rainfall band.
2022, 48(11):1449-1459.
DOI: 10.7519/j.issn.1000-0526.2022.050901
Abstract:
Based on the observation of Parsivel disdrometer at Shangqiu Station in Henan Province, Feicheng and Shouguang stations in Shandong Province, Lushun and Changhai stations in Liaoning Province, the raindrop size distributions of Typhoon Rumbia after landfall in 2018 are analyzed. The results show that Shangqiu, Feicheng and Shouguang stations have the similar characteristics of the average raindrop size distribution at different rain intensities with high concentration of small raindrops and low concentration of large raindrops, and part of the average drop size distributions have the characteristics of balanced raindrop size distributions. On the contrary, the average raindrop size distributions at Lushun and Changhai stations have low concentration of small raindrops and high concentration of large raindrops, and the average raindrop size distribution is controlled by ice phase. The Z-R relation of Shangqiu, Feicheng and Shouguang stations are similar, and the Z-R relation between Lushun and Changhai is similar. There is a great difference in indexes between the two types, indicating that the microphysical characteristics of precipitation are obviously different.The parameter of normalized Gamma distribution of raindrop size distribution shows that the convective precipitations in Shangqiu, Feicheng and Shouguang have the characteristics of maritime raindrop size distribution, and the microphysical processes are mainly of warm rain process, which is dominated by the coalescence growth, and the mixing of warm rain and ice phase. By contrast, the convective precipitations at Lushun and Changhai stations have the characteristics of continental raindrop size distribution, and the microphysical processes are predominated by the ice phase and the mixing of warm rain and ice phase.The above analyses indicate that although the Typhoon Rumbia in Henan and Shandong provinces were affected by cold air continuously, there was no obvious change in the microphysical characteristics, the cloud microphysical process changed significantly after it weakened into an extratropical cyclone.
Based on the observation of Parsivel disdrometer at Shangqiu Station in Henan Province, Feicheng and Shouguang stations in Shandong Province, Lushun and Changhai stations in Liaoning Province, the raindrop size distributions of Typhoon Rumbia after landfall in 2018 are analyzed. The results show that Shangqiu, Feicheng and Shouguang stations have the similar characteristics of the average raindrop size distribution at different rain intensities with high concentration of small raindrops and low concentration of large raindrops, and part of the average drop size distributions have the characteristics of balanced raindrop size distributions. On the contrary, the average raindrop size distributions at Lushun and Changhai stations have low concentration of small raindrops and high concentration of large raindrops, and the average raindrop size distribution is controlled by ice phase. The Z-R relation of Shangqiu, Feicheng and Shouguang stations are similar, and the Z-R relation between Lushun and Changhai is similar. There is a great difference in indexes between the two types, indicating that the microphysical characteristics of precipitation are obviously different.The parameter of normalized Gamma distribution of raindrop size distribution shows that the convective precipitations in Shangqiu, Feicheng and Shouguang have the characteristics of maritime raindrop size distribution, and the microphysical processes are mainly of warm rain process, which is dominated by the coalescence growth, and the mixing of warm rain and ice phase. By contrast, the convective precipitations at Lushun and Changhai stations have the characteristics of continental raindrop size distribution, and the microphysical processes are predominated by the ice phase and the mixing of warm rain and ice phase.The above analyses indicate that although the Typhoon Rumbia in Henan and Shandong provinces were affected by cold air continuously, there was no obvious change in the microphysical characteristics, the cloud microphysical process changed significantly after it weakened into an extratropical cyclone.
ZHANG Zulian
,
MAO Weiyi
,
ZHANG Shanqing
,
WANG Mingquan
,
TANG Ye
,
AIDAITULI Mushajiang
,
TUERGONG Yusupu
2022, 48(11):1460-1474.
DOI: 10.7519/j.issn.1000-0526.2022.042102
Abstract:
Using the 0.05°×0.05° temperature grid forecast guidance products issued by China Meteorological Administration and the hourly temperature data of land surface data assimilation system (CLDAS), this paper designs three intelligent grid temperature forecast correction algorithms based on the average filtering and corrects the 3 h temperature forecasts with 240 h lead time starting from 20:00 BT every day in the northern Xinjiang Plain from April to May 2019. Then the forecast effect of three kinds of revised products and guidance forecast products are compared and tested. The results show that the accuracy and stability of air temperature and frost forecast were obviously improved after the three filtering corrections. In the results of time-division test, compared with the original guide forecast product, the root mean square error (RMSE) of the three corrected products decreased by 0.79, 0.85 and 0.88℃ on average, the accuracy of temperature forecast increased by 6.11%, 6.38% and 6.46% on average, the accuracy of frost forecast increased by 3.00%, 5.81% and 7.31% on average, respectively. Moreover, the RMSE of 24 h frost forecast decreased by 4.21, 4.41 and 4.35 h, respectively. In the regional test results, the RMSE of the temperature of the three revised products decreased by 0.66, 0.71 and 0.90℃, and the accuracy of the temperature forecast increased by 5.7%, 6.1% and 6.1%, respectively. The accuracy of frost forecast increased significantly in the area of 600-1200 m above sea level in the southeast of Junggar Basin, increasing by 2.5%, 4.8% and 5.4% respectively, but not obvious in other frost areas. The RMSE of 24 h frost duration forecast was reduced by 0.81, 0.63 and 0.56 h. In comparison, the effect of the revised forecasts by the optimal ensemble algorithm is the best.
Using the 0.05°×0.05° temperature grid forecast guidance products issued by China Meteorological Administration and the hourly temperature data of land surface data assimilation system (CLDAS), this paper designs three intelligent grid temperature forecast correction algorithms based on the average filtering and corrects the 3 h temperature forecasts with 240 h lead time starting from 20:00 BT every day in the northern Xinjiang Plain from April to May 2019. Then the forecast effect of three kinds of revised products and guidance forecast products are compared and tested. The results show that the accuracy and stability of air temperature and frost forecast were obviously improved after the three filtering corrections. In the results of time-division test, compared with the original guide forecast product, the root mean square error (RMSE) of the three corrected products decreased by 0.79, 0.85 and 0.88℃ on average, the accuracy of temperature forecast increased by 6.11%, 6.38% and 6.46% on average, the accuracy of frost forecast increased by 3.00%, 5.81% and 7.31% on average, respectively. Moreover, the RMSE of 24 h frost forecast decreased by 4.21, 4.41 and 4.35 h, respectively. In the regional test results, the RMSE of the temperature of the three revised products decreased by 0.66, 0.71 and 0.90℃, and the accuracy of the temperature forecast increased by 5.7%, 6.1% and 6.1%, respectively. The accuracy of frost forecast increased significantly in the area of 600-1200 m above sea level in the southeast of Junggar Basin, increasing by 2.5%, 4.8% and 5.4% respectively, but not obvious in other frost areas. The RMSE of 24 h frost duration forecast was reduced by 0.81, 0.63 and 0.56 h. In comparison, the effect of the revised forecasts by the optimal ensemble algorithm is the best.
2022, 48(11):1475-1486.
DOI: 10.7519/j.issn.1000-0526.2022.052601
Abstract:
Affected by the westerly trough, subtropical high pressure and Typhoon Lichma, a localized heavy rainstorm occurred in Gaotang County on the West Shandong Plain from 20:00 BT 9 to 08:00 BT 10 August 2019. Based on FY-4A satellite cloud images, ECMWF numerical forecasts, dual-polarization Doppler radar data, ADTD lightning system positioning data, regional station minute rainfall, raindrop size distribution as well as the Beijing 3 km regional model products, this paper analyzes the causes for the localized heavy rainstorm in Gaotang and the microphysical characteristics of the severe precipitation. The conclusions are as follows. Before the localized heavy rainstorm, obvious cracks appeared in the westerly trough cloud belt at the bottom of which cold airs diffused to the front of the trough, forming a meso-α scale low-altitude shear line with the warm and humid airflow in front of the trough. In the early stage of the localized heavy rainstorm, due to the superposition of the downdraft outflow of strong shear line convection and the cold air diffusing from the bottom layer, the outflow boundary echo zone quickly moved away from the parent body so that the strong shear line echo zone was placed on the bottom cold air cushion and weakened quickly. The convection triggered by the outflow boundary and the quasi-linear pair of echoes formed by the warm and humid air advancing to the northwest were all dominated by convective precipitation. The precipitation intensity was high, the duration was short and the accumulated rainfall was small, but due to the different properties of the bottom layer, there were obvious differences in their raindrop size distribution. The low-altitude shear line was maintained for a long time, causing warm and humid air to accumulate continuously and forming a large value area of θse on the warm side of the shear line. At the beginning of the severe precipitation, the vertical upward movement on the shear line was significantly enhanced, and the maximum upward speed at 925 hPa was higher than 1.5 Pa·s-1, and two meso-β scale cyclone disturbances were formed, triggering the release of environmental instability energy and the deep moist convection. Cloud images and echoes show that the severe precipitation cloud clusters moved through the rainstorm area successively along the shear line, producing the “train effect” and thus resulting in the severe precipitation near Gaotang. After the westerly trough and shear line echoes combined, relatively abundant supercooled water kept maintaining at 6-10 km above Gaotang, promoting the growths of ice crystals and precipitation particles and making the precipitation intensity stronger, the peak of heavy precipitation widened, and the ground precipitation increased significantly. During the localized heavy rainstorm, there was an obvious double-peak structure in the scale spectrum of ground raindrops. The peak position with raindrop diameter at 1.2 mm was stable relatively while the other peak was at the end of the small raindrops with diameters at 0.3-0.5 mm. Statistical analysis suggests that the time series of large raindrops is synchronized with the time series of minute precipitation, and the correlation coefficient reaches 0.9867. The time series of small raindrops lags behind the time series of minute precipitation by 2 minutes.
Affected by the westerly trough, subtropical high pressure and Typhoon Lichma, a localized heavy rainstorm occurred in Gaotang County on the West Shandong Plain from 20:00 BT 9 to 08:00 BT 10 August 2019. Based on FY-4A satellite cloud images, ECMWF numerical forecasts, dual-polarization Doppler radar data, ADTD lightning system positioning data, regional station minute rainfall, raindrop size distribution as well as the Beijing 3 km regional model products, this paper analyzes the causes for the localized heavy rainstorm in Gaotang and the microphysical characteristics of the severe precipitation. The conclusions are as follows. Before the localized heavy rainstorm, obvious cracks appeared in the westerly trough cloud belt at the bottom of which cold airs diffused to the front of the trough, forming a meso-α scale low-altitude shear line with the warm and humid airflow in front of the trough. In the early stage of the localized heavy rainstorm, due to the superposition of the downdraft outflow of strong shear line convection and the cold air diffusing from the bottom layer, the outflow boundary echo zone quickly moved away from the parent body so that the strong shear line echo zone was placed on the bottom cold air cushion and weakened quickly. The convection triggered by the outflow boundary and the quasi-linear pair of echoes formed by the warm and humid air advancing to the northwest were all dominated by convective precipitation. The precipitation intensity was high, the duration was short and the accumulated rainfall was small, but due to the different properties of the bottom layer, there were obvious differences in their raindrop size distribution. The low-altitude shear line was maintained for a long time, causing warm and humid air to accumulate continuously and forming a large value area of θse on the warm side of the shear line. At the beginning of the severe precipitation, the vertical upward movement on the shear line was significantly enhanced, and the maximum upward speed at 925 hPa was higher than 1.5 Pa·s-1, and two meso-β scale cyclone disturbances were formed, triggering the release of environmental instability energy and the deep moist convection. Cloud images and echoes show that the severe precipitation cloud clusters moved through the rainstorm area successively along the shear line, producing the “train effect” and thus resulting in the severe precipitation near Gaotang. After the westerly trough and shear line echoes combined, relatively abundant supercooled water kept maintaining at 6-10 km above Gaotang, promoting the growths of ice crystals and precipitation particles and making the precipitation intensity stronger, the peak of heavy precipitation widened, and the ground precipitation increased significantly. During the localized heavy rainstorm, there was an obvious double-peak structure in the scale spectrum of ground raindrops. The peak position with raindrop diameter at 1.2 mm was stable relatively while the other peak was at the end of the small raindrops with diameters at 0.3-0.5 mm. Statistical analysis suggests that the time series of large raindrops is synchronized with the time series of minute precipitation, and the correlation coefficient reaches 0.9867. The time series of small raindrops lags behind the time series of minute precipitation by 2 minutes.
2022, 48(11):1487-1496.
DOI: 10.7519/j.issn.1000-0526.2022.102101
Abstract:
The main characteristics of the general atmospheric circulation in August 2022 are as follows. There were two polar vortex centers in the Northern Hemisphere and they were stronger than normal. The circulation at middle-high latitudes of the Eurasia showed a latitudinal type, and the ridge to the north of Caspian Sea was unusually strong. The western Pacific subtropical high was stronger than that of the climatological normal, and its location was more westerly compared to that in normal years. The monthly mean temperature across China was 22.4℃, higher than normal (21.1℃) by 1.3℃, and the monthly mean precipitation was 82.4 mm, 23.1% lower than normal (107.1 mm). During this month, the high temperature days in China were abnormally more as the result of the persistent influence of the regional high temperature events. The meteorological drought condition in the Yangtze River Basin and other places continued to develop. Five tropical cyclones were active over the South China Sea and the western North Pacific, among which Typhoon Mulan (No.2207) and Typhoon Ma-on (No.2209) made landfall in China, but generally the number of landfall typhoon was less than usual. Convection events occurred frequently and there were eight torrential rain processes in this month, causing localized serious damages.
The main characteristics of the general atmospheric circulation in August 2022 are as follows. There were two polar vortex centers in the Northern Hemisphere and they were stronger than normal. The circulation at middle-high latitudes of the Eurasia showed a latitudinal type, and the ridge to the north of Caspian Sea was unusually strong. The western Pacific subtropical high was stronger than that of the climatological normal, and its location was more westerly compared to that in normal years. The monthly mean temperature across China was 22.4℃, higher than normal (21.1℃) by 1.3℃, and the monthly mean precipitation was 82.4 mm, 23.1% lower than normal (107.1 mm). During this month, the high temperature days in China were abnormally more as the result of the persistent influence of the regional high temperature events. The meteorological drought condition in the Yangtze River Basin and other places continued to develop. Five tropical cyclones were active over the South China Sea and the western North Pacific, among which Typhoon Mulan (No.2207) and Typhoon Ma-on (No.2209) made landfall in China, but generally the number of landfall typhoon was less than usual. Convection events occurred frequently and there were eight torrential rain processes in this month, causing localized serious damages.
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