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CN 11-2282/P
CN 11-2282/P
Volume 49,2023 Issue 9
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2023,49(9):1029-1044, DOI: 10.7519/j.issn.1000-0526.2023.050602
Abstract:
Affected by the strong cold air in 19-24 February 2022, an extreme cold event occurred in Yunnan, which was characterized by sharp drop in temperature， affecting large areas and lasting a long time. In this paper, the extreme characteristics of the cold event and the evolution characteristics of the upper and lower atmospheric circulation during the process are analyzed by using the data of 124 meteorological observation stations in Yunnan, the reanalysis data of NCEP/NCAR and ERA5 atmospheric circulation. The results show that this cold event was very extreme, and was the second strongest cold wave weather event in Yunnan in recent ten years. The cold air intensity at 69 stations reached the cold wave standard, of which the daily average temperature at 10 stations reached or broke the lowest temperature record in February. During the cold event, the rainy and snowy weather was prominent, the accumulated precipitation in the process was close to the climatological precipitation in February, and the scope of a single day snowfall was the largest in recent 20 years. The factors that affected the strong cold event were extremely complex. The cold air activity was closely related to the strengthening and evolution of the atmosphere circulation system in mid high latitudes, such as the Ural high ridge, the East Asia trough, the Asian upper air westerly jet, the Siberian high, and was also associated with the eastward propagation of the subtropical abnormal Rossby wave train which was originated from the North Atlantic Region. This abnormal Rossby wave train played an important role in guiding the southward dispersion of wave energy and the southward movement of cold air in the Tibetan Plateau, and had a certain impact on the strengthening of southwest water vapor transport in front of the south branch trough. Meanwhile, the convective activities in the tropics also had a certain impact on the strengthening of cold air in East Asia. During the cold event, the cold air flew southward along the northeast path, influencing Yunnan. The intersection of cold and warm air in Yunnan was very prominent, resulting in significant cooling, rain and snow during the cold event.
Affected by the strong cold air in 19-24 February 2022, an extreme cold event occurred in Yunnan, which was characterized by sharp drop in temperature， affecting large areas and lasting a long time. In this paper, the extreme characteristics of the cold event and the evolution characteristics of the upper and lower atmospheric circulation during the process are analyzed by using the data of 124 meteorological observation stations in Yunnan, the reanalysis data of NCEP/NCAR and ERA5 atmospheric circulation. The results show that this cold event was very extreme, and was the second strongest cold wave weather event in Yunnan in recent ten years. The cold air intensity at 69 stations reached the cold wave standard, of which the daily average temperature at 10 stations reached or broke the lowest temperature record in February. During the cold event, the rainy and snowy weather was prominent, the accumulated precipitation in the process was close to the climatological precipitation in February, and the scope of a single day snowfall was the largest in recent 20 years. The factors that affected the strong cold event were extremely complex. The cold air activity was closely related to the strengthening and evolution of the atmosphere circulation system in mid high latitudes, such as the Ural high ridge, the East Asia trough, the Asian upper air westerly jet, the Siberian high, and was also associated with the eastward propagation of the subtropical abnormal Rossby wave train which was originated from the North Atlantic Region. This abnormal Rossby wave train played an important role in guiding the southward dispersion of wave energy and the southward movement of cold air in the Tibetan Plateau, and had a certain impact on the strengthening of southwest water vapor transport in front of the south branch trough. Meanwhile, the convective activities in the tropics also had a certain impact on the strengthening of cold air in East Asia. During the cold event, the cold air flew southward along the northeast path, influencing Yunnan. The intersection of cold and warm air in Yunnan was very prominent, resulting in significant cooling, rain and snow during the cold event.
2023,49(9):1045-1062, DOI: 10.7519/j.issn.1000-0526.2023.062801
Abstract:
In this study, NCEP/NCAR FNL 0.25°×0.25° reanalysis data, GDAS 1°×1° reanalysis data, the fused hourly precipitation of satellite and radar, conventional weather data of Xinjiang, FY-2G satellite data, the GPS-observed PWV data and the HYSPLIT trajectory model are used to conduct an in-depth analysis of extreme precipitation events that occurred in the southeastern Hami Area of Xinjiang on 31 July 2018 (hereinafter referred to as the 31 July process) and in the northern Hami Area on 8 August 2016 (hereinafter referred to as the 8 August process). Based on calculations of water vapor transport stream function, potential function, water vapor transport trajectories, water vapor budge, the characteristics of large-scale water vapor transport and convergence during two severe rainfall events are analyzed. The results show that the two events both occurred in the situation of abnormal continental high, which provided a favorable circulation background for long-distance water vapor transport. The water vapor transports in both of the severe rainfall events consisted of three stages, and the Hexi Corridor water vapor transport contributed to the water vapor supply in both events. Before and during the 31 July process, affected by the easterly water vapor transport channel, there was an obviously humidification at stations of Hami Area and Gansu Province from southeast to northwest. The transport and supplement of water vapor from low latitude provided an abundant water vapor supply for the short-time severe rainfall in southeastern Hami Area. Comparatively, before and during the 8 August process, the water vapor transport channel from northern Tibetan Plateau to southern Bazhou Area in Xinjiang was established. The water vapor in Tibetan Plateau was carried toward north, joining in the water vapor taken by southwest airflow in front of the trough. At the same time, with the low-level water vapor from Hexi Corridor, three humidification processes were triggered in northern Hami Area.
In this study, NCEP/NCAR FNL 0.25°×0.25° reanalysis data, GDAS 1°×1° reanalysis data, the fused hourly precipitation of satellite and radar, conventional weather data of Xinjiang, FY-2G satellite data, the GPS-observed PWV data and the HYSPLIT trajectory model are used to conduct an in-depth analysis of extreme precipitation events that occurred in the southeastern Hami Area of Xinjiang on 31 July 2018 (hereinafter referred to as the 31 July process) and in the northern Hami Area on 8 August 2016 (hereinafter referred to as the 8 August process). Based on calculations of water vapor transport stream function, potential function, water vapor transport trajectories, water vapor budge, the characteristics of large-scale water vapor transport and convergence during two severe rainfall events are analyzed. The results show that the two events both occurred in the situation of abnormal continental high, which provided a favorable circulation background for long-distance water vapor transport. The water vapor transports in both of the severe rainfall events consisted of three stages, and the Hexi Corridor water vapor transport contributed to the water vapor supply in both events. Before and during the 31 July process, affected by the easterly water vapor transport channel, there was an obviously humidification at stations of Hami Area and Gansu Province from southeast to northwest. The transport and supplement of water vapor from low latitude provided an abundant water vapor supply for the short-time severe rainfall in southeastern Hami Area. Comparatively, before and during the 8 August process, the water vapor transport channel from northern Tibetan Plateau to southern Bazhou Area in Xinjiang was established. The water vapor in Tibetan Plateau was carried toward north, joining in the water vapor taken by southwest airflow in front of the trough. At the same time, with the low-level water vapor from Hexi Corridor, three humidification processes were triggered in northern Hami Area.
2023,49(9):1063-1074, DOI: 10.7519/j.issn.1000-0526.2023.070801
Abstract:
Using conventional observation data, ground automatic weather station data, Doppler weather radar and wind profiler radar data, etc., this paper analyzes the EF2 tornado that occurred in Jinghai, Tianjin at about 17:30 BT 31 August 2018. The focus is on the analysis of environmental background conditions, local instability conditions, trigger uplift conditions and radar echo characteristics, etc. before and after the occurrence of tornado. The results show that this tornado weather occurred when the 500 hPa high-altitude trough moved eastward, the subtropical high strengthened its westward movement and Typhoon Capricorn was moving northward. Before the tornado occurred, the environmental background conditions were obviously unstable, the CAPE value was 1797 J·kg-1 (CIN was 0 J·kg-1) and the wind vector difference in the height of 0-6 km was approximately 14 m·s-1 and there was lower lifting condensation level (LCL). At the same time, there was high CAPE (maximum value exceeded 4000 J·kg-1), lower LCL. Before the tornado occurred, LCL showed a sudden drop (lowest to around 897 hPa). With the occurrence of tornado, the vertical wind shear values near the ground (0-1 km height and below) at both upwind and downwind stations showed the characteristics of rapid increase first and then rapid decrease. The rapid decrease of the vertical wind shear value started from the upper layer and descended rapidly, while the vertical wind shear value above the 0-1 km height did not change significantly. Doppler weather radar observations show that the tornado echo had a small individual scale (with a diameter of about 2 km at the positive and negative velocity centers), a maximum rotational speed of 24 m·s-1 at the positive and negative velocity centers, and a vertical vorticity of 2.4×10-2 s-1. The echo of this tornado had obvious overhanging structure, bounded weak echo zone and tornado vortex. Moreover, the low-level inflow at the rear side was very strong, so it should be a micro supercell tornado. The collision between the sea breeze front moving to the locale and the gust front formed by the upwind thunderstorm cell outflow triggered the vigorous release of unstable energy locally, stimulating the regeneration of thunderstorm cells, and developing into organized strong thunderstorm cells, which should be the direct trigger conditions for the occurrence of this tornado.
Using conventional observation data, ground automatic weather station data, Doppler weather radar and wind profiler radar data, etc., this paper analyzes the EF2 tornado that occurred in Jinghai, Tianjin at about 17:30 BT 31 August 2018. The focus is on the analysis of environmental background conditions, local instability conditions, trigger uplift conditions and radar echo characteristics, etc. before and after the occurrence of tornado. The results show that this tornado weather occurred when the 500 hPa high-altitude trough moved eastward, the subtropical high strengthened its westward movement and Typhoon Capricorn was moving northward. Before the tornado occurred, the environmental background conditions were obviously unstable, the CAPE value was 1797 J·kg-1 (CIN was 0 J·kg-1) and the wind vector difference in the height of 0-6 km was approximately 14 m·s-1 and there was lower lifting condensation level (LCL). At the same time, there was high CAPE (maximum value exceeded 4000 J·kg-1), lower LCL. Before the tornado occurred, LCL showed a sudden drop (lowest to around 897 hPa). With the occurrence of tornado, the vertical wind shear values near the ground (0-1 km height and below) at both upwind and downwind stations showed the characteristics of rapid increase first and then rapid decrease. The rapid decrease of the vertical wind shear value started from the upper layer and descended rapidly, while the vertical wind shear value above the 0-1 km height did not change significantly. Doppler weather radar observations show that the tornado echo had a small individual scale (with a diameter of about 2 km at the positive and negative velocity centers), a maximum rotational speed of 24 m·s-1 at the positive and negative velocity centers, and a vertical vorticity of 2.4×10-2 s-1. The echo of this tornado had obvious overhanging structure, bounded weak echo zone and tornado vortex. Moreover, the low-level inflow at the rear side was very strong, so it should be a micro supercell tornado. The collision between the sea breeze front moving to the locale and the gust front formed by the upwind thunderstorm cell outflow triggered the vigorous release of unstable energy locally, stimulating the regeneration of thunderstorm cells, and developing into organized strong thunderstorm cells, which should be the direct trigger conditions for the occurrence of this tornado.
2023,49(9):1075-1084, DOI: 10.7519/j.issn.1000-0526.2023.072401
Abstract:
Based on the Shandong S-band dual polarization Doppler weather radar data, sounding data and surface precipitation observation as well as the environmental background features, severe rainstorms are divided into the thunderstorm gale (accompanied by severe precipitation or hail) dominated type (referred to as “mixed type”) and the simple severe precipitation dominated type (referred to as “precipitation dominated type”). Three types of minute precipitation magnitudes are considered for each type of rainstorm, and comparative analysis of the low-level dual polarization parameter characteristics of severe rainstorms in the six different scenarios is conducted in this paper. The results show that as the magnitude of minute precipitation increases, the low-level reflectivity factor (ZH) and specific differential phase (KDP) of both types of severe rainstorms increase. The differential reflectivity (ZDR) and correlation coefflicient (CC) of “precipitation dominated type” rainstorms do not show significant changes, while the ZDR and CC of “mixed type” storms decrease. This indicates that with the increase in magnitude of precipitation, the number of large-size hails in the lower layers of “mixed type” severe rainstorms increases, resulting in the decrease in ZDR and CC. For high-intensity precipitation above 2 mm·min-1， the low-level ZH, ZDR, and KDP of “mixed type” rainstorm are concentrated at 50.5-57.0 dBz, 1.7-2.7 dB, 2.4-4.3°·km-1, and CC is above 0.960， while the low-level ZH, ZDR, and KDP of the “precipitation dominated type” rainstorm are concentrated at 49.5-53.5 dBz，〖JP〗 1.2-2.1 dB, 2.5-3.9°·km-1 with CC above 0.970. This means that most “mixed type” rainstorms contain a large amount of small-size hails around 5-10 mm during high-intensity precipitation. These smaller hailstones tend to melt into larger rain droplets in the lower layers, increasing the ZDR value and also making the echo intensity ZH higher than that of the “precipitation dominated type”. At the same minute precipitation level, the low-level ZH and ZDR of the “mixed type” rainstorm are greater than those of the “precipitation dominated type” storm, and CC is smaller than that of the “precipitation dominated type” storm. This is because the former owns not only more 5-10 mm smaller hailstone but also some large hail particles. The larger KDP in the lower layer of rainstorms has obvious indicative significance for the two types of severe precipitation.
Based on the Shandong S-band dual polarization Doppler weather radar data, sounding data and surface precipitation observation as well as the environmental background features, severe rainstorms are divided into the thunderstorm gale (accompanied by severe precipitation or hail) dominated type (referred to as “mixed type”) and the simple severe precipitation dominated type (referred to as “precipitation dominated type”). Three types of minute precipitation magnitudes are considered for each type of rainstorm, and comparative analysis of the low-level dual polarization parameter characteristics of severe rainstorms in the six different scenarios is conducted in this paper. The results show that as the magnitude of minute precipitation increases, the low-level reflectivity factor (ZH) and specific differential phase (KDP) of both types of severe rainstorms increase. The differential reflectivity (ZDR) and correlation coefflicient (CC) of “precipitation dominated type” rainstorms do not show significant changes, while the ZDR and CC of “mixed type” storms decrease. This indicates that with the increase in magnitude of precipitation, the number of large-size hails in the lower layers of “mixed type” severe rainstorms increases, resulting in the decrease in ZDR and CC. For high-intensity precipitation above 2 mm·min-1， the low-level ZH, ZDR, and KDP of “mixed type” rainstorm are concentrated at 50.5-57.0 dBz, 1.7-2.7 dB, 2.4-4.3°·km-1, and CC is above 0.960， while the low-level ZH, ZDR, and KDP of the “precipitation dominated type” rainstorm are concentrated at 49.5-53.5 dBz，〖JP〗 1.2-2.1 dB, 2.5-3.9°·km-1 with CC above 0.970. This means that most “mixed type” rainstorms contain a large amount of small-size hails around 5-10 mm during high-intensity precipitation. These smaller hailstones tend to melt into larger rain droplets in the lower layers, increasing the ZDR value and also making the echo intensity ZH higher than that of the “precipitation dominated type”. At the same minute precipitation level, the low-level ZH and ZDR of the “mixed type” rainstorm are greater than those of the “precipitation dominated type” storm, and CC is smaller than that of the “precipitation dominated type” storm. This is because the former owns not only more 5-10 mm smaller hailstone but also some large hail particles. The larger KDP in the lower layer of rainstorms has obvious indicative significance for the two types of severe precipitation.
2023,49(9):1085-1096, DOI: 10.7519/j.issn.1000-0526.2023.052501
Abstract:
Long-time series of Doppler radar products of Yinchuan from May to September of 2011-2016 are used to analyze the climatic characteristics of convective storms in northern Ningxia. The results indicate that 77% of all convective storms in northern Ningxia lasted for no more than 30 min and moved at a speed of 9-13 m·s-1. Most of them mainly moved eastward at higher speeds compared to the moving speeds in other directions. The maximum reflectivity factor of convective storms was concentrated between 35-50 dBz, the echo top height was between 5-9 km, and the vertical integrated liquid water content was generally less than 10 kg·m-2. The 500 hPa wind was the steering flow of convective storms. The probability of convective storm occurrence was lower when 500 hPa and 700 hPa were controlled by northerly winds, but relatively high when controlled by southerly winds. July was the peak month for convective storms, and the peak hours were 12:00 BT to 13:00 BT. Helan Mountain was the area with the highest occurrence of convective storms, followed by the sandy areas from the central-north of Lingwu to the north of Otog Front Banner. The distribution of convective storms was not uniform in Helan Mountain, and the most frequent occurrence was in the areas between high mountains and deep valleys.
Long-time series of Doppler radar products of Yinchuan from May to September of 2011-2016 are used to analyze the climatic characteristics of convective storms in northern Ningxia. The results indicate that 77% of all convective storms in northern Ningxia lasted for no more than 30 min and moved at a speed of 9-13 m·s-1. Most of them mainly moved eastward at higher speeds compared to the moving speeds in other directions. The maximum reflectivity factor of convective storms was concentrated between 35-50 dBz, the echo top height was between 5-9 km, and the vertical integrated liquid water content was generally less than 10 kg·m-2. The 500 hPa wind was the steering flow of convective storms. The probability of convective storm occurrence was lower when 500 hPa and 700 hPa were controlled by northerly winds, but relatively high when controlled by southerly winds. July was the peak month for convective storms, and the peak hours were 12:00 BT to 13:00 BT. Helan Mountain was the area with the highest occurrence of convective storms, followed by the sandy areas from the central-north of Lingwu to the north of Otog Front Banner. The distribution of convective storms was not uniform in Helan Mountain, and the most frequent occurrence was in the areas between high mountains and deep valleys.
2023,49(9):1097-1107, DOI: 10.7519/j.issn.1000 0526.2023.062702
Abstract:
Based on the typhoon data of Shanghai Typhoon Institute and the daily typhoon precipitation data of national stations of China during 1961-2020, the climatic characteristics of different levels of typhoon precipitation caused by typhoon passing though Taiwan Island in southeast coastal of China including Zhejiang, Fujian and Guangdong provinces are statistically analyzed, and the causes for the differences in extreme precipitation are discussed.The study results show that 90% of the typhoons passing though Taiwan Island can bring rainstorms to the southeast coastal area of China. There are 1.6 typhoon rainstrom events every year. The interannual variation of the daily maximum precipitation amount of shows an obvious increasing trend. Especially, the rainstrom extreme events have increased significantly since 2003.The variation of monthly frequency of daily precipitation at different levels shows a single peak pattern, and the peak months are from July to September.The occurrence frequency of the daily maximum precipitation at different levels shows that the frequency of extreme precipitation over 100 mm decreases with the increase of precipitation intensity, and the frequency of extreme precipitation over 300 mm decreases obviously. In terms of spatial distribution, the daily rainstorm frequency shows an uneven and rapid decrease from the coastal areas to the inland areas.The rainstorms from the typhoon through Taiwan Island have most prominent impact on the northern coast of Fujian Province, and Zherong Station in Fujian is the extreme rainstorm center. Based on NCEP reanalysis data, the large scale environmental comparison of the difference between the two similar typhoon groups shows that to the heavy precipitation typhoon group, strong wind speed area on the north side of the typhoon center leads to strong onshore winds. With the effect of mountain terrain, there is stronger convergence and very strong deep vertical upward movement, in front of mountains. With better moisture conditions, theupward motion can take the low level high energy water vapor to the middle high levels. The precipitation dynamics and water vapor conditions are significantly stronger than those of the weak precipitation typhoon group, thus resulting in more typhoon rainstorms.
Based on the typhoon data of Shanghai Typhoon Institute and the daily typhoon precipitation data of national stations of China during 1961-2020, the climatic characteristics of different levels of typhoon precipitation caused by typhoon passing though Taiwan Island in southeast coastal of China including Zhejiang, Fujian and Guangdong provinces are statistically analyzed, and the causes for the differences in extreme precipitation are discussed.The study results show that 90% of the typhoons passing though Taiwan Island can bring rainstorms to the southeast coastal area of China. There are 1.6 typhoon rainstrom events every year. The interannual variation of the daily maximum precipitation amount of shows an obvious increasing trend. Especially, the rainstrom extreme events have increased significantly since 2003.The variation of monthly frequency of daily precipitation at different levels shows a single peak pattern, and the peak months are from July to September.The occurrence frequency of the daily maximum precipitation at different levels shows that the frequency of extreme precipitation over 100 mm decreases with the increase of precipitation intensity, and the frequency of extreme precipitation over 300 mm decreases obviously. In terms of spatial distribution, the daily rainstorm frequency shows an uneven and rapid decrease from the coastal areas to the inland areas.The rainstorms from the typhoon through Taiwan Island have most prominent impact on the northern coast of Fujian Province, and Zherong Station in Fujian is the extreme rainstorm center. Based on NCEP reanalysis data, the large scale environmental comparison of the difference between the two similar typhoon groups shows that to the heavy precipitation typhoon group, strong wind speed area on the north side of the typhoon center leads to strong onshore winds. With the effect of mountain terrain, there is stronger convergence and very strong deep vertical upward movement, in front of mountains. With better moisture conditions, theupward motion can take the low level high energy water vapor to the middle high levels. The precipitation dynamics and water vapor conditions are significantly stronger than those of the weak precipitation typhoon group, thus resulting in more typhoon rainstorms.
2023,49(9):1108-1118, DOI: 10.7519/j.issn.1000-0526.2023.082801
Abstract:
Two extreme heat events, caused sequentially by continental high and subtropical high, occurred in Chongqing in the midsummer of 2022. Based on surface observation data and ERA5 reanalysis data, the differences in high temperature characteristics between the two stages dominated by continental high and subtropical high are compared and analyzed. The results show that during the short stage of continental high domination, the heating process was developing with less intensity, high relative humidity and bigger diurnal temperature range. During the long stage of subtropical high domination, the heat event exhibited great extremity, grew severe with pronounced xerothermic characteristics and nocturnal warming. The diagnosis of thermodynamic equation reveals that when the continental high was dominant, diabatic heating and vertical motion jointly contributed to the warming, while when subtropical high set in, diabatic heating and heat advection became the primary and secondary factors for the diurnal warming, and the contribution of vertical motion became insignificant. At night, as the dry adiabatic or super-adiabatic layer at lower level abated and vanished, the warming effect induced by downward motion on the northern side of Yunnan-Guizhou Plateau drastically intensified. The surface thermodynamic difference suggests that the surface latent heat flux decreased and sensible heat flux increased significantly under the domination of subtropical high than under the continental high. The increasing surface sensible heat directly heated the atmosphere, intensively driving up the surface temperature.
Two extreme heat events, caused sequentially by continental high and subtropical high, occurred in Chongqing in the midsummer of 2022. Based on surface observation data and ERA5 reanalysis data, the differences in high temperature characteristics between the two stages dominated by continental high and subtropical high are compared and analyzed. The results show that during the short stage of continental high domination, the heating process was developing with less intensity, high relative humidity and bigger diurnal temperature range. During the long stage of subtropical high domination, the heat event exhibited great extremity, grew severe with pronounced xerothermic characteristics and nocturnal warming. The diagnosis of thermodynamic equation reveals that when the continental high was dominant, diabatic heating and vertical motion jointly contributed to the warming, while when subtropical high set in, diabatic heating and heat advection became the primary and secondary factors for the diurnal warming, and the contribution of vertical motion became insignificant. At night, as the dry adiabatic or super-adiabatic layer at lower level abated and vanished, the warming effect induced by downward motion on the northern side of Yunnan-Guizhou Plateau drastically intensified. The surface thermodynamic difference suggests that the surface latent heat flux decreased and sensible heat flux increased significantly under the domination of subtropical high than under the continental high. The increasing surface sensible heat directly heated the atmosphere, intensively driving up the surface temperature.
2023,49(9):1119-1130, DOI: 10.7519/j.issn.1000-0526.2023.053102
Abstract:
Using the maximum temperature observation data, Meiyu data and NCEP/NCAR reanalysis data, we analyze the interdecadal variation characteristics of high temperature stations in Yangtze River Basin and the corresponding atmospheric circulation anomaly at different periods of summer from 1961 to 2020. The results show that high temperature events mainly occurred in the middle-east part (east of 105°E) of the Yangtze River Basin. There existed an abrupt mutation in the summer high temperature across this basin around 2002. Relative to the 35℃ threshold, the increments of high temperature stations at 37℃ and 40℃ were more obvious before and after the mutation. But interdecadal variation characteristics at different periods of summer were inconsistent, and they can be divided into two categories: the slow increasing periods without significant interdecadal turnings and the quick increasing periods, in which an abrupt mutation occurred around 2002 and the interdacadal relative change rates were higher than that of the whole season of summer. The Eurasian teleconnection, the East Asia-Pacific teleconnection and the end time of Meiyu were the major contributors to the intraseasonal inconsistency. During the quick increasing periods, the significant interdecadal increase of high temperature was always accompanied by abnormal intensification of East Asia-Pacific teleconnection. The circulations in the mid-high latitude over Eurasia were significantly different between the two periods with the largest relative change rates. During the slow increasing periods, however, Eurasian teleconnection strengthened at a lower magnitude, while East Asia-Pacific teleconnection was weakened. The slow increase of high temperature stations in 9-19 July was related to the late end of Meiyu.
Using the maximum temperature observation data, Meiyu data and NCEP/NCAR reanalysis data, we analyze the interdecadal variation characteristics of high temperature stations in Yangtze River Basin and the corresponding atmospheric circulation anomaly at different periods of summer from 1961 to 2020. The results show that high temperature events mainly occurred in the middle-east part (east of 105°E) of the Yangtze River Basin. There existed an abrupt mutation in the summer high temperature across this basin around 2002. Relative to the 35℃ threshold, the increments of high temperature stations at 37℃ and 40℃ were more obvious before and after the mutation. But interdecadal variation characteristics at different periods of summer were inconsistent, and they can be divided into two categories: the slow increasing periods without significant interdecadal turnings and the quick increasing periods, in which an abrupt mutation occurred around 2002 and the interdacadal relative change rates were higher than that of the whole season of summer. The Eurasian teleconnection, the East Asia-Pacific teleconnection and the end time of Meiyu were the major contributors to the intraseasonal inconsistency. During the quick increasing periods, the significant interdecadal increase of high temperature was always accompanied by abnormal intensification of East Asia-Pacific teleconnection. The circulations in the mid-high latitude over Eurasia were significantly different between the two periods with the largest relative change rates. During the slow increasing periods, however, Eurasian teleconnection strengthened at a lower magnitude, while East Asia-Pacific teleconnection was weakened. The slow increase of high temperature stations in 9-19 July was related to the late end of Meiyu.
2023,49(9):1131-1141, DOI: 10.7519/j.issn.1000-0526.2023.070301
Abstract:
Based on the hourly maximum temperature observations from 19 national meteorological stations during the summers of 2008-2021, this paper analyzes the spatial distribution of high temperature (HT) hours and the features of interdecadal, intraseasonal and diurnal variabilities in Beijing. The results show that the numbers of both HT days and HT hours are much greater in the dountown area and the south of the city, but less in the north and west parts as the result of the combined influences of topography and urban heat island effect. Among them, the Haidian, Fengtai and Changping districts are the most concentrated areas of HT days and hours. On the intraseasonal scale, the HT hours in Beijing are mainly concentrated in the period from late mid-June to early mid-July, which is the period before the beginning of the rainy season in North China. The first dekad of July is the most concentrated period of HT activities. On the diurnal variation, the HT activities can be seen mainly from 09:00 BT to 21:00 BT, particularly concentrated from 14:00 BT to 17:00 BT. In addition, linear regression is also employed in this paper to fit the relationship between maximum temperature and HT hours. The correlation coefficient between the fitting result and the observation reaches as high as 0.82. In Beijing, for each 1℃ increase in maximum temperature over the 35℃ threshold, the HT hours increase by about 1.7 hours. The HT hours in Beijing also exhibits an obvious interdecadal variability. The distribution of the differences of accumulated summer HT hours between 2015-2021 and 2008-2014 is quite different from the spatial distribution of HT hours in climatic state. The area with large interdecadal differences is not located at the central part of HT days or HT hours. Relative to the period of 2008-2014, the HT hours in 2015-2021 are commonly added from 11:00 BT to 19:00 BT, which means the HT periods in Beijing tend to start earlier and end later in the latter period.
Based on the hourly maximum temperature observations from 19 national meteorological stations during the summers of 2008-2021, this paper analyzes the spatial distribution of high temperature (HT) hours and the features of interdecadal, intraseasonal and diurnal variabilities in Beijing. The results show that the numbers of both HT days and HT hours are much greater in the dountown area and the south of the city, but less in the north and west parts as the result of the combined influences of topography and urban heat island effect. Among them, the Haidian, Fengtai and Changping districts are the most concentrated areas of HT days and hours. On the intraseasonal scale, the HT hours in Beijing are mainly concentrated in the period from late mid-June to early mid-July, which is the period before the beginning of the rainy season in North China. The first dekad of July is the most concentrated period of HT activities. On the diurnal variation, the HT activities can be seen mainly from 09:00 BT to 21:00 BT, particularly concentrated from 14:00 BT to 17:00 BT. In addition, linear regression is also employed in this paper to fit the relationship between maximum temperature and HT hours. The correlation coefficient between the fitting result and the observation reaches as high as 0.82. In Beijing, for each 1℃ increase in maximum temperature over the 35℃ threshold, the HT hours increase by about 1.7 hours. The HT hours in Beijing also exhibits an obvious interdecadal variability. The distribution of the differences of accumulated summer HT hours between 2015-2021 and 2008-2014 is quite different from the spatial distribution of HT hours in climatic state. The area with large interdecadal differences is not located at the central part of HT days or HT hours. Relative to the period of 2008-2014, the HT hours in 2015-2021 are commonly added from 11:00 BT to 19:00 BT, which means the HT periods in Beijing tend to start earlier and end later in the latter period.
2023,49(9):1142-1148, DOI: 10.7519/j.issn.1000-0526.2023.042002
Abstract:
In 2022, the global mean temperature was about 1.15℃ (±0.13℃) above pre-industrial levels, making it the fifth warmest year. Sea level continued to rise in an upward trend. Arctic Sea ice was below normal and Antarctic Sea ice reached a record low. Pakistan, South Korea, India, Bangladesh, eastern Australia, Brazil, and central and southern Africa suffered rainstorm and floods. The Sahel Region and most of East Africa experienced severe drought. Europe, China, United States, Japan, Pakistan and India experienced record-breaking heat waves. North America and Europe were hit by cold surges and snow storms. Severe convective weather frequently hit parts of the world. A total of 40 tropical cyclones were generated around the world, the number and intensity of which were both lower than the climatic average. Causal analysis indicates that in July, the abnormally strong subtropical high belt in the Northern Hemisphere, along with the persistent and intense warm high-pressure system over Europe, resulted in prevailing subsiding air currents throughout the European Region’s troposphere. This led to record-breaking heat waves across multiple areas in Europe. From July to August, the abnormally strong and westward-shifted western Pacific subtropical high system, along with a redirection of moisture transport from the eastern part of the Bay of Bengal towards northern India and Pakistan, led to intense lower-level moisture convergence with the combined action of the South Asian and East Asian summer monsoons. This prolonged the maintenance of extreme precipitation events and led to the occurrence of severe flood disasters.
In 2022, the global mean temperature was about 1.15℃ (±0.13℃) above pre-industrial levels, making it the fifth warmest year. Sea level continued to rise in an upward trend. Arctic Sea ice was below normal and Antarctic Sea ice reached a record low. Pakistan, South Korea, India, Bangladesh, eastern Australia, Brazil, and central and southern Africa suffered rainstorm and floods. The Sahel Region and most of East Africa experienced severe drought. Europe, China, United States, Japan, Pakistan and India experienced record-breaking heat waves. North America and Europe were hit by cold surges and snow storms. Severe convective weather frequently hit parts of the world. A total of 40 tropical cyclones were generated around the world, the number and intensity of which were both lower than the climatic average. Causal analysis indicates that in July, the abnormally strong subtropical high belt in the Northern Hemisphere, along with the persistent and intense warm high-pressure system over Europe, resulted in prevailing subsiding air currents throughout the European Region’s troposphere. This led to record-breaking heat waves across multiple areas in Europe. From July to August, the abnormally strong and westward-shifted western Pacific subtropical high system, along with a redirection of moisture transport from the eastern part of the Bay of Bengal towards northern India and Pakistan, led to intense lower-level moisture convergence with the combined action of the South Asian and East Asian summer monsoons. This prolonged the maintenance of extreme precipitation events and led to the occurrence of severe flood disasters.
2023,49(9):1149-1156, DOI: 10.7519/j.issn.1000-0526.2023.081701
Abstract:
The main characteristics of atmospheric circulation in the Northern Hemisphere exhibited a multipolar distribution of polar vortices in June 2023. The 500 hPa geopotential height field over the Ural Mountains was significantly weaker than the climatological average for the same period. The Western Pacific subtropical high was located more northward and westward than the normal situation. The average precipitation in June was 86.7 mm, which is 16% less than normal; and the least rainfall amount for the same period since 2005. The national average temperature was 21.1℃, showing a positive anomaly of 0.7℃, the second-highest since 1961. During this month, there were five regional torrential rain events mainly in Southwest China and the areas south of the Jianghuai Region. During this month, five large-scale high-temperature processes influence the western and northern parts of China. Moreover, seven severe convective weather events occurred in the provinces of Liaoning, Jilin, Jiangsu, Anhui, Guangdong and Guangxi. In terms of typhoon, there was only one generated in June, the least in June on record. What’s more, the decreased precipitation and higher temperature worsened the drought condition in the northern part of China.
The main characteristics of atmospheric circulation in the Northern Hemisphere exhibited a multipolar distribution of polar vortices in June 2023. The 500 hPa geopotential height field over the Ural Mountains was significantly weaker than the climatological average for the same period. The Western Pacific subtropical high was located more northward and westward than the normal situation. The average precipitation in June was 86.7 mm, which is 16% less than normal; and the least rainfall amount for the same period since 2005. The national average temperature was 21.1℃, showing a positive anomaly of 0.7℃, the second-highest since 1961. During this month, there were five regional torrential rain events mainly in Southwest China and the areas south of the Jianghuai Region. During this month, five large-scale high-temperature processes influence the western and northern parts of China. Moreover, seven severe convective weather events occurred in the provinces of Liaoning, Jilin, Jiangsu, Anhui, Guangdong and Guangxi. In terms of typhoon, there was only one generated in June, the least in June on record. What’s more, the decreased precipitation and higher temperature worsened the drought condition in the northern part of China.
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Available online: September 22, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.082901
Abstract:
Based on the daily observation of precipitation and sunshine data from China Meteorological Administration and the NCEP/NCAR Reanalysis Project, this paper analyzes the extreme features of a high-impact “wheat-soaked” persistent rainfall event in the Huang-Huai-Hai region in late May of 2023 and the atmospheric circulation patterns. For the area average of five provinces during 21-31 May, the sunshine duration is more extreme than the total precipitation, with the second lowest in the research period of 1961-2023. However, obvious difference exists among the five provinces. Among them, Henan Province has the most severe disaster. To compare both the weather condition and the circulation pattern with historical events, this paper proposes an objective definition of “wheat-soaked rainfall” event in Henan Province for the first time and selected 18 typical cases during 1981-2023. For the event in late May 2023, it has the sixth highest rainfall amount and the second lowest sunshine duration among all events. Composition of general circulation patterns displays a more westward-northward and stronger western Pacific subtropical high (WPSH), and a “lower in the west while higher in the east” geopotential height anomaly in the mid-high latitudes of Eurasia. In contrast, the circulation pattern in late May 2023 is similar to that of the historical events in the mid-high latitudes. However, in the tropical region, under the influence of super typhoon “Mawar”, the western part of the WPSH is squeezed and deformed, and the southwest moisture transportation in the northwest part of the WPSH is much stronger. At the same time, the southeasterly flow along the northeast side of “Mawar” was also quite strong and persistent owing to the its stable stay over the east of the Philippines. The two water vapor channels superposed and caused the low-level moisture converge over the Huang-Huai-Hai region and led to persistent precipitation and long-time absence of sunshine.
Based on the daily observation of precipitation and sunshine data from China Meteorological Administration and the NCEP/NCAR Reanalysis Project, this paper analyzes the extreme features of a high-impact “wheat-soaked” persistent rainfall event in the Huang-Huai-Hai region in late May of 2023 and the atmospheric circulation patterns. For the area average of five provinces during 21-31 May, the sunshine duration is more extreme than the total precipitation, with the second lowest in the research period of 1961-2023. However, obvious difference exists among the five provinces. Among them, Henan Province has the most severe disaster. To compare both the weather condition and the circulation pattern with historical events, this paper proposes an objective definition of “wheat-soaked rainfall” event in Henan Province for the first time and selected 18 typical cases during 1981-2023. For the event in late May 2023, it has the sixth highest rainfall amount and the second lowest sunshine duration among all events. Composition of general circulation patterns displays a more westward-northward and stronger western Pacific subtropical high (WPSH), and a “lower in the west while higher in the east” geopotential height anomaly in the mid-high latitudes of Eurasia. In contrast, the circulation pattern in late May 2023 is similar to that of the historical events in the mid-high latitudes. However, in the tropical region, under the influence of super typhoon “Mawar”, the western part of the WPSH is squeezed and deformed, and the southwest moisture transportation in the northwest part of the WPSH is much stronger. At the same time, the southeasterly flow along the northeast side of “Mawar” was also quite strong and persistent owing to the its stable stay over the east of the Philippines. The two water vapor channels superposed and caused the low-level moisture converge over the Huang-Huai-Hai region and led to persistent precipitation and long-time absence of sunshine.
Available online: September 19, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.030703
Abstract:
Sub-seasonal to seasonal (S2S) climate and runoff prediction is of great importance for active disaster reduction. The prediction models of runoff anomaly and extreme drought are developed based on S2S climate model by National Climate Center, China Meteorological Administration, and a hydrological model HBV. The performance of the models are evaluated with indices of MSSS, ACC, AUC and BSS for hindcast, and verified for the runoff anomaly prediction over the Yellow River Basin in 2021. The results suggest that runoff mean prediction during the next 40 days is skillful, and the skill is higher in dry season than wet season. Moreover, the extreme drought prediction is skillful in later autumn (November) and the months in winter (DJF). The direction of monthly runoff anomaly during May to October in 2021 were predicted correctly except for June and September. Finally, the analysis of skill variation with lead time and seasons, and the skill difference between runoff and precipitation reveals that the skill of precipitation prediction by S2S climate model influences runoff skill, especially during wet season. However, other factors than precipitation have effects on the skill of runoff prediction.
Sub-seasonal to seasonal (S2S) climate and runoff prediction is of great importance for active disaster reduction. The prediction models of runoff anomaly and extreme drought are developed based on S2S climate model by National Climate Center, China Meteorological Administration, and a hydrological model HBV. The performance of the models are evaluated with indices of MSSS, ACC, AUC and BSS for hindcast, and verified for the runoff anomaly prediction over the Yellow River Basin in 2021. The results suggest that runoff mean prediction during the next 40 days is skillful, and the skill is higher in dry season than wet season. Moreover, the extreme drought prediction is skillful in later autumn (November) and the months in winter (DJF). The direction of monthly runoff anomaly during May to October in 2021 were predicted correctly except for June and September. Finally, the analysis of skill variation with lead time and seasons, and the skill difference between runoff and precipitation reveals that the skill of precipitation prediction by S2S climate model influences runoff skill, especially during wet season. However, other factors than precipitation have effects on the skill of runoff prediction.
Available online: September 19, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.080302
Abstract:
Based on the operational real-time typhoon data of National Meteorological Center and other sources of observations including the ERA-Interim reanalysis data by 6 hours from the European Centre for Medium-Range Weather Forecasts, the main characteristics of typhoon activity in the Northwest Pacific in 2022 are analyzed and reviewed. It is found that in 2022, the characteristics of typhoon activity in stages and clusters are obvious, with the genesis region being northward and westward, and the number of typhoons landing in China is relatively less and the intensity is relatively stronger than the average. The main track errors come from the initial stage of typhoon generation, the combination of typhoon and westerlies, and the period of multi typhoon or low pressure area activity. Further analysis of the forecast difficulties of Chaba, Muifa and Hinnamor reveals that: (1)The continental high and upper level jet to the north of Chaba is the key system leading to the long-time track adjustment of Chaba at the early stage of its generation; (2)The track errors of the Muifa after landfall is due to the deviation of the model"s forecast of the Steering flows; (3)The track and intensity of Hinnamor are complex, and China Meteorological Administration (CMA) has forecast deviations in the rate of its rapid intensifying and weakening, intensity fluctuations due to structure and size changes.
Based on the operational real-time typhoon data of National Meteorological Center and other sources of observations including the ERA-Interim reanalysis data by 6 hours from the European Centre for Medium-Range Weather Forecasts, the main characteristics of typhoon activity in the Northwest Pacific in 2022 are analyzed and reviewed. It is found that in 2022, the characteristics of typhoon activity in stages and clusters are obvious, with the genesis region being northward and westward, and the number of typhoons landing in China is relatively less and the intensity is relatively stronger than the average. The main track errors come from the initial stage of typhoon generation, the combination of typhoon and westerlies, and the period of multi typhoon or low pressure area activity. Further analysis of the forecast difficulties of Chaba, Muifa and Hinnamor reveals that: (1)The continental high and upper level jet to the north of Chaba is the key system leading to the long-time track adjustment of Chaba at the early stage of its generation; (2)The track errors of the Muifa after landfall is due to the deviation of the model"s forecast of the Steering flows; (3)The track and intensity of Hinnamor are complex, and China Meteorological Administration (CMA) has forecast deviations in the rate of its rapid intensifying and weakening, intensity fluctuations due to structure and size changes.
Available online: September 18, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.091201
Abstract:
To investigate the mesoscale features and formation mechanism of the thunderstorm that occurred on 30 April 2021 in Hangzhou Bay Area,the data of conventional air sounding observation data,minute-level automatic weather station(AWS) data,wind radar profile,Doppler weather radar are analyzed,and focuses on the evolution and mesoscale features of the convective system after its moving into Hangzhou Bay.The case shows that this severe squall line developed under a multiscale interaction background of anomalously deep northeast cold vortex at relatively high altitude,extremely intensified northwest jet at mid-level and surface warm low pressure,which induces an enhancement of the local convection storms behind the squall line,resulting in thunderstorm.After the process of crossing the Hangzhou Bay,the convection cell intensity is enhancing,the warm-moist southerly flow at front of the gust front and the cold pool at the rear of gust front developed stronger, barometric pressure surged, with the thermodynamic conditions influence of surface of Hangzhou Bay and surface environmental wind field, triggered unstable energy which contribute to enhance the development of cell.The intensity of subsidence divergence outflow develop stronger after the cell crossing Hangzhou Bay contributing to the high momentum in the middle layer was brought to the ground.Therefore the enhancement effect of extreme winds which in the south of Hangzhou Bay is significant. The smaller friction on the water surface of Hangzhou Bay and special topography of bell mouth,were the important reasons for the increasing of wind speed.At the same time, minute-by-minute temperature change is about 7-10 minutes earlier than the occurrence time of extreme wind,which has certain directive significance for local extreme wind monitoring and warning.
To investigate the mesoscale features and formation mechanism of the thunderstorm that occurred on 30 April 2021 in Hangzhou Bay Area,the data of conventional air sounding observation data,minute-level automatic weather station(AWS) data,wind radar profile,Doppler weather radar are analyzed,and focuses on the evolution and mesoscale features of the convective system after its moving into Hangzhou Bay.The case shows that this severe squall line developed under a multiscale interaction background of anomalously deep northeast cold vortex at relatively high altitude,extremely intensified northwest jet at mid-level and surface warm low pressure,which induces an enhancement of the local convection storms behind the squall line,resulting in thunderstorm.After the process of crossing the Hangzhou Bay,the convection cell intensity is enhancing,the warm-moist southerly flow at front of the gust front and the cold pool at the rear of gust front developed stronger, barometric pressure surged, with the thermodynamic conditions influence of surface of Hangzhou Bay and surface environmental wind field, triggered unstable energy which contribute to enhance the development of cell.The intensity of subsidence divergence outflow develop stronger after the cell crossing Hangzhou Bay contributing to the high momentum in the middle layer was brought to the ground.Therefore the enhancement effect of extreme winds which in the south of Hangzhou Bay is significant. The smaller friction on the water surface of Hangzhou Bay and special topography of bell mouth,were the important reasons for the increasing of wind speed.At the same time, minute-by-minute temperature change is about 7-10 minutes earlier than the occurrence time of extreme wind,which has certain directive significance for local extreme wind monitoring and warning.
Available online: September 13, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.060402
Abstract:
Basedonthe hourly precipitation data in the wet season during 2011-2020 from gradient observation system between Cangshan Mountain and Erhai lake ofDali National Climate Observatory,thediurnalvariationcharacteristicsof precipitation atthemountainpeak, hillsideand dam areawere analyzed. The results showthat the diurnal variation of rainfall amount at the dam area station presented one peak, while that at mountain side and hilltop stations presented two peaks.The diurnal variation of rainfall frequency at dam area and hilltop stations displayed a single peak, while that hillside station was relatively stable. All hourly rainfall amount and rainfall frequency for a whole day basically increased with the increase of altitudes.The diurnal variation of rainfall intensity at hilltop station exhibited double peaks, while that at the hillside and dam area stations showed remarkable fluctuation with small values in the afternoon and large values in the night.There was no significant difference in rainfall intensity from 14:00 to 17:00among the three stations, but the rainfall intensity at the hillside and dam-region stations was obviously greater than that at the hilltop station during other periods.The rainfall amount in the night with a duration of 2-16h was a large value area, and which had a longer duration with the increase of altitude. The rainfall amount during the daytime with a duration of less than 6 h was a large value area, and the occurrence of the large value was delayed with the increase of altitude.The rainfall frequency at the three stations had a large value area during the day and night when the duration was less than 6 h, while that at the hilltop station only had a large value area at night when the duration was 7-18 h.The rainfall frequency in the night were greater than that during the day at the dam area and hilltop stations, while there was little difference in the rainfall frequency during the day and night at the hillside station.The cumulative rainfall amount and frequency of long (medium and short) duration increased (decreased) with the increase of altitudes.The contribution of long duration rainfall amount (rainfall frequency) to accumulated rainfall amount (rainfall frequency) at each station was the largest,and short duration rainfall amount (medium duration rainfall frequency) was the least.
Basedonthe hourly precipitation data in the wet season during 2011-2020 from gradient observation system between Cangshan Mountain and Erhai lake ofDali National Climate Observatory,thediurnalvariationcharacteristicsof precipitation atthemountainpeak, hillsideand dam areawere analyzed. The results showthat the diurnal variation of rainfall amount at the dam area station presented one peak, while that at mountain side and hilltop stations presented two peaks.The diurnal variation of rainfall frequency at dam area and hilltop stations displayed a single peak, while that hillside station was relatively stable. All hourly rainfall amount and rainfall frequency for a whole day basically increased with the increase of altitudes.The diurnal variation of rainfall intensity at hilltop station exhibited double peaks, while that at the hillside and dam area stations showed remarkable fluctuation with small values in the afternoon and large values in the night.There was no significant difference in rainfall intensity from 14:00 to 17:00among the three stations, but the rainfall intensity at the hillside and dam-region stations was obviously greater than that at the hilltop station during other periods.The rainfall amount in the night with a duration of 2-16h was a large value area, and which had a longer duration with the increase of altitude. The rainfall amount during the daytime with a duration of less than 6 h was a large value area, and the occurrence of the large value was delayed with the increase of altitude.The rainfall frequency at the three stations had a large value area during the day and night when the duration was less than 6 h, while that at the hilltop station only had a large value area at night when the duration was 7-18 h.The rainfall frequency in the night were greater than that during the day at the dam area and hilltop stations, while there was little difference in the rainfall frequency during the day and night at the hillside station.The cumulative rainfall amount and frequency of long (medium and short) duration increased (decreased) with the increase of altitudes.The contribution of long duration rainfall amount (rainfall frequency) to accumulated rainfall amount (rainfall frequency) at each station was the largest,and short duration rainfall amount (medium duration rainfall frequency) was the least.
Abstract:
The round-trip horizontal drift radiosonde can do the three-stage observation of "ascending-drifting-descending stages" by releasing a sounding balloon at only once time. In particular, the descending stage increases the vertical observation of the atmosphere at 06UTC and 18UTC respectively, which has the potential to significantly improve the prediction skills of the regional high-resolution rapid assimilation cycle prediction system at 06UTC and 18UTC. In order to realize the assimilation of the round-trip horizontal drift sounding in the high-resolution regional model and analyze its impacts on the forecast, one vertical thinning method by ‘selecting the closest observation according to the model layer’for assimilation is preliminarily proposed, and the influence of this thinning method on model analysis is deeply analyzed. On this basis, a one-month batch assimilation impact experiments are carried out by using the networked observations in the middle and lower reaches of the Yangtze River and the impacts on model forecasts are detailed investigated. The results of the thinning sensitivity tests show that compared with the assimilation of traditional operational soundings, the analysis and prediction root mean squared errors (RMSE) of the assimilation of non-thinning round-trip horizontal drift radiosonde observations are significantly increased, and the precipitation prediction scores are also significantly declined. On the contrary, the performance of analysis and prediction fields are improved by assimilating the data after thinning，which indicate that the vertical sparsity of round-trip horizontal drift radiosonde observations must be carried out before assimilation. The results of batch experiments show that at the cold start time (00UTC and 12UTC, time with conventional radiosonde), the assimilation of round-trip horizontal drift sounding (ascending stage) observations has little change in analysis error and prediction error than assimilation of traditional operational radiosonde data. At the warm start time (03UTC, 06UTC, 09UTC, 15UTC, 18UTC, 21UTC, time without conventional radiosonde), compared with the control experiment, the accuracy of the analysis field is improved by about 0.4 % by assimilating the descending section of the horizontal drift sounding data . The ETS scores of the 12-hour cumulative precipitation forecast of 0-12 hours change little, and the ETS scores of the 12-hour cumulative precipitation forecast at 0.1 mm, 1.0 mm, 5.0 mm, 10.0 mm and 25.0 mm threshold increase by about 0.5 %. Moreover, the ETS scores at 50.00 mm threshold increased by about 2.3 %. All above results show that the round-trip horizontal drift sounding must be thinned before assimilation, and the assimilation of the round-trip horizontal drift sounding can improve the precipitation forecast skill of the regional high-resolution rapid assimilation cycle forecast system at the warm start time.
The round-trip horizontal drift radiosonde can do the three-stage observation of "ascending-drifting-descending stages" by releasing a sounding balloon at only once time. In particular, the descending stage increases the vertical observation of the atmosphere at 06UTC and 18UTC respectively, which has the potential to significantly improve the prediction skills of the regional high-resolution rapid assimilation cycle prediction system at 06UTC and 18UTC. In order to realize the assimilation of the round-trip horizontal drift sounding in the high-resolution regional model and analyze its impacts on the forecast, one vertical thinning method by ‘selecting the closest observation according to the model layer’for assimilation is preliminarily proposed, and the influence of this thinning method on model analysis is deeply analyzed. On this basis, a one-month batch assimilation impact experiments are carried out by using the networked observations in the middle and lower reaches of the Yangtze River and the impacts on model forecasts are detailed investigated. The results of the thinning sensitivity tests show that compared with the assimilation of traditional operational soundings, the analysis and prediction root mean squared errors (RMSE) of the assimilation of non-thinning round-trip horizontal drift radiosonde observations are significantly increased, and the precipitation prediction scores are also significantly declined. On the contrary, the performance of analysis and prediction fields are improved by assimilating the data after thinning，which indicate that the vertical sparsity of round-trip horizontal drift radiosonde observations must be carried out before assimilation. The results of batch experiments show that at the cold start time (00UTC and 12UTC, time with conventional radiosonde), the assimilation of round-trip horizontal drift sounding (ascending stage) observations has little change in analysis error and prediction error than assimilation of traditional operational radiosonde data. At the warm start time (03UTC, 06UTC, 09UTC, 15UTC, 18UTC, 21UTC, time without conventional radiosonde), compared with the control experiment, the accuracy of the analysis field is improved by about 0.4 % by assimilating the descending section of the horizontal drift sounding data . The ETS scores of the 12-hour cumulative precipitation forecast of 0-12 hours change little, and the ETS scores of the 12-hour cumulative precipitation forecast at 0.1 mm, 1.0 mm, 5.0 mm, 10.0 mm and 25.0 mm threshold increase by about 0.5 %. Moreover, the ETS scores at 50.00 mm threshold increased by about 2.3 %. All above results show that the round-trip horizontal drift sounding must be thinned before assimilation, and the assimilation of the round-trip horizontal drift sounding can improve the precipitation forecast skill of the regional high-resolution rapid assimilation cycle forecast system at the warm start time.
Available online: September 12, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.082701
Abstract:
This paper aims to improve the numerical modeling of vertical turbulent transport of water vapor and sensible heat in atmospheric boundary layer and also the simulation of fog, the three-dimensional non-hydrostatic WRF model, with the help of a scale-aware MYNN_SA scheme of both local and non-local turbulences, was used to simulate a dense foggy weather process in a broad region from Northern China to Yangtz-Huai river during 28 and 29 December 1997. Impacts of the scale-aware boundary-layer turbulent scheme on the development of stable boundary layer, turbulent transport and the simulation of fog are focused in a model resolution from meso-scale to large eddy. Compared with the surface observations in China and the ERA5 data, the scale-aware MYNN_SA scheme improved the results of sub-grid-scale turbulent mixing when model resolution closes to the gray-zone scale, which shows better fog intensity, spatial and temporal variation of the dense fog in comparison with the original MYNN scheme. Detailed vertical structures of the fog, liquid cloud water and temperature inversion are well simulated by using the scale-aware MYNN_SA scheme.
This paper aims to improve the numerical modeling of vertical turbulent transport of water vapor and sensible heat in atmospheric boundary layer and also the simulation of fog, the three-dimensional non-hydrostatic WRF model, with the help of a scale-aware MYNN_SA scheme of both local and non-local turbulences, was used to simulate a dense foggy weather process in a broad region from Northern China to Yangtz-Huai river during 28 and 29 December 1997. Impacts of the scale-aware boundary-layer turbulent scheme on the development of stable boundary layer, turbulent transport and the simulation of fog are focused in a model resolution from meso-scale to large eddy. Compared with the surface observations in China and the ERA5 data, the scale-aware MYNN_SA scheme improved the results of sub-grid-scale turbulent mixing when model resolution closes to the gray-zone scale, which shows better fog intensity, spatial and temporal variation of the dense fog in comparison with the original MYNN scheme. Detailed vertical structures of the fog, liquid cloud water and temperature inversion are well simulated by using the scale-aware MYNN_SA scheme.
Available online: September 08, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.081601
Abstract:
By using the object-oriented method of Contiguous Rain Area(CRA), this paper investigates the forecast error components of rainfall and their variation trends for different thresholds and forecast periods for typhoons influencing China in 2019. The correlation between typhoon track errors and displacement errors of rainfall objects is analyzed and the performance improvements of rainfall forecasts calculated with track correction or CRA shifting are compared. Finally forecast errors of rainfall probability distribution around typhoons, radial and asymmetric rainfall distribution are verified and analyzed. The results are as follows: (1) For different forecast periods and rainfall thresholds, the main forecast errors come from displacement error D and pattern error P and rotation error R is minimum. (2) Except for larger rainfall, track error is significantly correlated with displacement error of CRA rainfall object. The improvement of rainfall forecasts made by track error correction is less than that made by CRA shifting correction. (3) The shape of probability density function for rainfall forecasts around typhoon coincides with the observed one. Before and after typhoon making landfall or approaching near coast, the forecasted rainfall intensities in typhoon core area are stronger than the observed ones while they are different out of typhoon core area. (4) Before and after typhoon making landfall or approaching near coast, the forecasted rainfall is closer to typhoon center than the observed one and lagged behind it. The asymmetric structure of the forecasted rainfall is significantly weaker than the observed one especially after typhoon making landfall or approaching near coast.
By using the object-oriented method of Contiguous Rain Area(CRA), this paper investigates the forecast error components of rainfall and their variation trends for different thresholds and forecast periods for typhoons influencing China in 2019. The correlation between typhoon track errors and displacement errors of rainfall objects is analyzed and the performance improvements of rainfall forecasts calculated with track correction or CRA shifting are compared. Finally forecast errors of rainfall probability distribution around typhoons, radial and asymmetric rainfall distribution are verified and analyzed. The results are as follows: (1) For different forecast periods and rainfall thresholds, the main forecast errors come from displacement error D and pattern error P and rotation error R is minimum. (2) Except for larger rainfall, track error is significantly correlated with displacement error of CRA rainfall object. The improvement of rainfall forecasts made by track error correction is less than that made by CRA shifting correction. (3) The shape of probability density function for rainfall forecasts around typhoon coincides with the observed one. Before and after typhoon making landfall or approaching near coast, the forecasted rainfall intensities in typhoon core area are stronger than the observed ones while they are different out of typhoon core area. (4) Before and after typhoon making landfall or approaching near coast, the forecasted rainfall is closer to typhoon center than the observed one and lagged behind it. The asymmetric structure of the forecasted rainfall is significantly weaker than the observed one especially after typhoon making landfall or approaching near coast.
Available online: September 05, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.062101
Abstract:
In order to analysis the simulated performance of CMA-MESO model for heavy rain occurred in Henan from 19 to 20 July 2021, not only the conventional observation, but also the unconventional observation as for radar and satellite used traditional and new spatial verified method that could reveal the deviation characteristics of convective storms and mesoscale convective systems (MCS, in satellite infrared channel) simulated by model, and then focus on the source of model deviation from the perspectives of water vapor, momentum, trigger and maintenance mechanism of precipitation. The results showed that: (1) the model could well capture the shape of the rain band, the duration of weak echoes and the evolution trend of intensity and area of MCS before main precipitation. (2)The model deviation appeared on that it underestimated the intensity of precipitation and failed to predict the extreme hourly precipitation at Zhengzhou station, also it misreported the evolution of hourly precipitation of main band and seriously underestimated the duration of convective storms and severe convective storms, as well as it missed the sharp increase of MCS area in the afternoon and the simulated location deviation of MCS was west and south.(3) The origin of model deviation was mainly owing to the simulation of water vapor, as for the vertical distribution of simulated water vapor was not appropriate, and the simulated water vapor transportation from Typhoon In-Fa and Typhoon Cempaka were both weak. In fact, the weak low-level jet and insufficient ultra low-level easterly jet pulsation mainly caused the insufficient of simulated water vapor transportation. Moreover, the failure to forecast the stably maintained convergence line at surface near zhengzhou station, combined with the deficiency of atmospheric instability and underestimation of unstable energy, making the convection not seriously developed and resulting in underestimated of precipitation.
In order to analysis the simulated performance of CMA-MESO model for heavy rain occurred in Henan from 19 to 20 July 2021, not only the conventional observation, but also the unconventional observation as for radar and satellite used traditional and new spatial verified method that could reveal the deviation characteristics of convective storms and mesoscale convective systems (MCS, in satellite infrared channel) simulated by model, and then focus on the source of model deviation from the perspectives of water vapor, momentum, trigger and maintenance mechanism of precipitation. The results showed that: (1) the model could well capture the shape of the rain band, the duration of weak echoes and the evolution trend of intensity and area of MCS before main precipitation. (2)The model deviation appeared on that it underestimated the intensity of precipitation and failed to predict the extreme hourly precipitation at Zhengzhou station, also it misreported the evolution of hourly precipitation of main band and seriously underestimated the duration of convective storms and severe convective storms, as well as it missed the sharp increase of MCS area in the afternoon and the simulated location deviation of MCS was west and south.(3) The origin of model deviation was mainly owing to the simulation of water vapor, as for the vertical distribution of simulated water vapor was not appropriate, and the simulated water vapor transportation from Typhoon In-Fa and Typhoon Cempaka were both weak. In fact, the weak low-level jet and insufficient ultra low-level easterly jet pulsation mainly caused the insufficient of simulated water vapor transportation. Moreover, the failure to forecast the stably maintained convergence line at surface near zhengzhou station, combined with the deficiency of atmospheric instability and underestimation of unstable energy, making the convection not seriously developed and resulting in underestimated of precipitation.
Available online: September 04, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.073001
Abstract:
In order to improve short-time strong rainfall forecast, the LightGBM algorithm is applied to build the hourly precipitation forecast model based on the precipitation observation data and CMA-GD-3km model forecast products of Fujian Province from April to September in 2019 and 2020. Correction models are optimized by features processing, Bagging (Bootstrap Aggregating) and hyperparameters search. Combined with AUC, AUPR and traditional classification indices, A series of experiments are designed to evaluate different modeling schemes and verify the applicability for short-time strong rainfall forecast. The results show that: (1) All modeling schemes improve the original numerical model forecast representing the high POD and FAR in varying degrees. Bagging can enhance the stability of model prediction, and the slightly unbalanced sub-training set contributes to better performance by reducing the FAR, the best TS score of validation set is about 17.5%. (2) The largest contribution to the classification information gain is K index, followed by 500hPa dew point and time parameters. (3) The ranking of experiment indices from good to bad: random cross-validation, random hourly cross-validation and operational simulation test, indicating that the validity of correction models mainly result from the sample information at the same or adjacent moments. (4) The dynamic fusion scheme of heterogeneous models based on logistic regression increases indices of static homogeneous models, which decreases at least 540,000 false alarm samples with approximately 50% POD.
In order to improve short-time strong rainfall forecast, the LightGBM algorithm is applied to build the hourly precipitation forecast model based on the precipitation observation data and CMA-GD-3km model forecast products of Fujian Province from April to September in 2019 and 2020. Correction models are optimized by features processing, Bagging (Bootstrap Aggregating) and hyperparameters search. Combined with AUC, AUPR and traditional classification indices, A series of experiments are designed to evaluate different modeling schemes and verify the applicability for short-time strong rainfall forecast. The results show that: (1) All modeling schemes improve the original numerical model forecast representing the high POD and FAR in varying degrees. Bagging can enhance the stability of model prediction, and the slightly unbalanced sub-training set contributes to better performance by reducing the FAR, the best TS score of validation set is about 17.5%. (2) The largest contribution to the classification information gain is K index, followed by 500hPa dew point and time parameters. (3) The ranking of experiment indices from good to bad: random cross-validation, random hourly cross-validation and operational simulation test, indicating that the validity of correction models mainly result from the sample information at the same or adjacent moments. (4) The dynamic fusion scheme of heterogeneous models based on logistic regression increases indices of static homogeneous models, which decreases at least 540,000 false alarm samples with approximately 50% POD.
Available online: August 31, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.083001
Abstract:
In Taipusi Banner of Xilin Gol League, Inner Mongolia, where suffered an EF3 strong tornado on June 25, 2021, which is very rare in history, resulting in 6 deaths and a large number of buildings and other serious damage.Based on meteorological observation data, ground encryption automatic station, CB-Doppler radar observation data of Zhangbei, Hebei Province, FY-4satellitedata and FNL (1°× 1°) reanalysis data of NECP every 6 h, this paper comprehensively analyzed the process of the strong tornado. The results show that the tornado occurs in the background of unstable stratification environment of the forward-tilted trough. The strong conditional instability of at the middle and low troposphere (the vertical temperature reduction rate of 850 hPa and 500 hPa is about 7.7 ℃·km -1), abundant water vapor in the lower layers, medium intensity convective available potential energy, and strong 0~6 km vertical wind shear are provide favorable environmental conditions for supercell storms and tornadoes.In addition, the 0~1 km vertical wind shear is 8 m·s -1, and the lifting condensation height (LCL) is 1.0 km, which provides relatively favorable environmental conditions for the occurrence of supercell storms and tornadoes. The convergence line accompanying the ground dry line triggered the parent storm that produced the tornado, and then evolved into the supercell. The radar reflectivity factor echo showed typical hook echo, the inflow gap of warm and wet air at low level, the weak echo region(WER) at low level, the overhang echo at middle and high level, and the moderate intensity mesocyclone and other characteristics. In the process of the formation and extinction of the tornado, three supercell storms formed successively, which all appeared in the isolated convective storm form. The tornado occurred at the top of one of the supercells, where is the junction of the front updraft and the rear downdraft. The possible start time and path of tornado based on the evolution of mesocyclone intensity analyzed by radar are in good agreement with the time of field investigation. Except for the strong tornado, this series of supercells also produced large hail and linear convection gale (thunderstorm gale), the strong echo center was significantly tilted from low to high, and the maximum reflectance factor was as high as 65 dBZ. In addition to the moderate strength mesyclones, there was also obvious mid-level radial convergence (MARC) of picture characters of radial velocity. At the time of supercell storm formation, the vertical liquid water content (VIL) is as high as 73 kg·m -2, the VIL density is 4～5 g·m -3. These radar echo characteristics indicate the presence of large hail, while the mid-level radial convergence is the radar echo characteristic of thunderstorm gale.
In Taipusi Banner of Xilin Gol League, Inner Mongolia, where suffered an EF3 strong tornado on June 25, 2021, which is very rare in history, resulting in 6 deaths and a large number of buildings and other serious damage.Based on meteorological observation data, ground encryption automatic station, CB-Doppler radar observation data of Zhangbei, Hebei Province, FY-4satellitedata and FNL (1°× 1°) reanalysis data of NECP every 6 h, this paper comprehensively analyzed the process of the strong tornado. The results show that the tornado occurs in the background of unstable stratification environment of the forward-tilted trough. The strong conditional instability of at the middle and low troposphere (the vertical temperature reduction rate of 850 hPa and 500 hPa is about 7.7 ℃·km -1), abundant water vapor in the lower layers, medium intensity convective available potential energy, and strong 0~6 km vertical wind shear are provide favorable environmental conditions for supercell storms and tornadoes.In addition, the 0~1 km vertical wind shear is 8 m·s -1, and the lifting condensation height (LCL) is 1.0 km, which provides relatively favorable environmental conditions for the occurrence of supercell storms and tornadoes. The convergence line accompanying the ground dry line triggered the parent storm that produced the tornado, and then evolved into the supercell. The radar reflectivity factor echo showed typical hook echo, the inflow gap of warm and wet air at low level, the weak echo region(WER) at low level, the overhang echo at middle and high level, and the moderate intensity mesocyclone and other characteristics. In the process of the formation and extinction of the tornado, three supercell storms formed successively, which all appeared in the isolated convective storm form. The tornado occurred at the top of one of the supercells, where is the junction of the front updraft and the rear downdraft. The possible start time and path of tornado based on the evolution of mesocyclone intensity analyzed by radar are in good agreement with the time of field investigation. Except for the strong tornado, this series of supercells also produced large hail and linear convection gale (thunderstorm gale), the strong echo center was significantly tilted from low to high, and the maximum reflectance factor was as high as 65 dBZ. In addition to the moderate strength mesyclones, there was also obvious mid-level radial convergence (MARC) of picture characters of radial velocity. At the time of supercell storm formation, the vertical liquid water content (VIL) is as high as 73 kg·m -2, the VIL density is 4～5 g·m -3. These radar echo characteristics indicate the presence of large hail, while the mid-level radial convergence is the radar echo characteristic of thunderstorm gale.
Available online: August 31, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.083101
Abstract:
The forecast results of radar echo extrapolation algorithm based on recurrent neural network are gradually blurred and distorted with time, and it is difficult to forecast the high echo area. To solve the above problems, this paper proposes a spatio-temporal long short-term memory network model based on context fusion and attention mechanism. The method fully extracts the short-term context information of different scales of radar image through the context fusion module. The attention module broadens the time perception domain of the prediction unit, so that the model perceives more time dynamics. Taking the weather radar data of Jiangsu Province from April to September in 2019-2021 as a sample, the spatio-temporal long short-term memory network based on context fusion and attention mechanism achieves better prediction performance through experimental comparison and analysis. The Critical Success Index (CSI) and Heidke Skill Score (HSS) reached 0.7611, 0.5326, 0.2369 and 0.7335, 0.5735, 0.3075, respectively, under the conditions of 60 minutes of extrapolation and thresholds of 10, 20 and 40 dBZ, which effectively improved the prediction accuracy.
The forecast results of radar echo extrapolation algorithm based on recurrent neural network are gradually blurred and distorted with time, and it is difficult to forecast the high echo area. To solve the above problems, this paper proposes a spatio-temporal long short-term memory network model based on context fusion and attention mechanism. The method fully extracts the short-term context information of different scales of radar image through the context fusion module. The attention module broadens the time perception domain of the prediction unit, so that the model perceives more time dynamics. Taking the weather radar data of Jiangsu Province from April to September in 2019-2021 as a sample, the spatio-temporal long short-term memory network based on context fusion and attention mechanism achieves better prediction performance through experimental comparison and analysis. The Critical Success Index (CSI) and Heidke Skill Score (HSS) reached 0.7611, 0.5326, 0.2369 and 0.7335, 0.5735, 0.3075, respectively, under the conditions of 60 minutes of extrapolation and thresholds of 10, 20 and 40 dBZ, which effectively improved the prediction accuracy.
Available online: August 31, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.083102
Abstract:
Based on conventional observation data, densely-distributed automatic weather station, Doppler weather radar data and ERA5 reanalysis data, the mesoscale cause of a rare extreme thunderstorm gale in Central area of Jilin Province on the morning of September 9,2021 was analyzed in detail. The results showed that: The squall line system that produced thunderstorm was formed by the deep northeast cold vortex and the large-scale frontogenesis at the tail of the cold front. The strong dry air in middle layer and the temperature decreasing rate closed to dry adiabatic below the inversion layer were conducive to the generation of severe wind. The existence of dry and warm cover leaded to rapid enhancement of low-level warm and humid air, and the CAPE value was more than 1600 J.kg-1 near the moment, which were conducive to the stratification becoming extremely unstable in a short period of time. The average wind speed in the entrainment layer was above 20 m.s-1, and the downward momentum transfer was beneficial to the enhancement of ground wind speed. The extreme thunderstorm gale occurred near the γ-scale vortex in the tail front of squall line after fracture, but the causes of severe wind at the two stations near the vortex were obviously different. The severe wind at Nongda station occurred when the air pressure dropped sharply, the temperature rose sharply and the minute precipitation was weak. It was caused by the strong sinking divergent airflow (cold pool outflow) in front of the squall line accelerating into the vortex under the action of strong southerly airflow, and the convergence updraft was rapidly enhanced. It was significantly different from the extreme thunderstorm gale caused by the strong sinking divergent airflow formed by the drag of precipitation particles at the nearby Nongboyuan Station and Changchun Station.
Based on conventional observation data, densely-distributed automatic weather station, Doppler weather radar data and ERA5 reanalysis data, the mesoscale cause of a rare extreme thunderstorm gale in Central area of Jilin Province on the morning of September 9,2021 was analyzed in detail. The results showed that: The squall line system that produced thunderstorm was formed by the deep northeast cold vortex and the large-scale frontogenesis at the tail of the cold front. The strong dry air in middle layer and the temperature decreasing rate closed to dry adiabatic below the inversion layer were conducive to the generation of severe wind. The existence of dry and warm cover leaded to rapid enhancement of low-level warm and humid air, and the CAPE value was more than 1600 J.kg-1 near the moment, which were conducive to the stratification becoming extremely unstable in a short period of time. The average wind speed in the entrainment layer was above 20 m.s-1, and the downward momentum transfer was beneficial to the enhancement of ground wind speed. The extreme thunderstorm gale occurred near the γ-scale vortex in the tail front of squall line after fracture, but the causes of severe wind at the two stations near the vortex were obviously different. The severe wind at Nongda station occurred when the air pressure dropped sharply, the temperature rose sharply and the minute precipitation was weak. It was caused by the strong sinking divergent airflow (cold pool outflow) in front of the squall line accelerating into the vortex under the action of strong southerly airflow, and the convergence updraft was rapidly enhanced. It was significantly different from the extreme thunderstorm gale caused by the strong sinking divergent airflow formed by the drag of precipitation particles at the nearby Nongboyuan Station and Changchun Station.
Available online: August 30, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.040101
Abstract:
In order to better carry out the monitoring and early warning of hail weather in Jiangxi, MICAPS weather map, Jiangxi meteorological automatic station data, Jiangxi radar mosaic data, single radar PUP product data, double multi wind field data inversion, strong echo automatic recognition, hail disaster photos and WeChat feedback video and other data are used, and the principles and methods of synoptic, radar meteorology, image recognition technology, etc. are adopted, The echo characteristics of hail in Jiangxi and surrounding provinces on March 14, 2022 are analyzed. The results show that: ① On March 14, hail occurred in many places in Jiangxi, strong wind ≥ 17.2 m/s appeared in 20 regional stations, precipitation ≥ 50.0 mm appeared in 24 regional stations, and thunderstorm strong wind and cold air strong wind mixed. ② 200 hPa high-altitude outflow area, 500 hPa south branch and wind shear, 850 hPa low vortex and shear line, ground convergence line and southwest inverted trough are obvious features of weather background; The higher CAPE value in Nanchang, the stronger inversion layer, the middle layer dry area and the lower layer wet area provide the environmental conditions for hail weather. ③ Hail is dominated by supercell echo, sometimes isolated, sometimes in echo group and echo band; Echo intensity ≥ 60 dBz and ≥ 70 dBz; Strong echo area: minimum ≥ 18 km2, maximum ≥ 180 km2; 30-60 dBz range strong echo gradient ≤ 6 km, with obvious cloud anvil echo structure; The life history of hail echo is more than 2 hours. ④ In hail echo recognition, vertical integration of liquid water content VIL is a very important feature. The VIL of Jiangxi hail single radar is 35 ～ 65 kg/m2, and the VIL on the radar puzzle is ≥ 35 kg/m2. ⑤ On the CAPPI chart of 2.5 km hail echo, the hail echo intensity is ≥ 60 dBz, and the maximum is 65 dBz; Most echo centers on double multi wind fields have the characteristics of middle vortex structure, side convergence wind field, north south wind field convergence, etc; Some wind farms are messy. ⑥ Scatter contour algorithm is adopted for automatic echo edge recognition; In each recognition, the thunderstorm echo group can identify multiple strong echoes at the same time, up to 19; ≥ 60 dBz echo area: minimum 18 km2, maximum 184 km2; Most cases showed echo nuclei of 65 dBz, the strongest being 73 dBz; The minimum and maximum echo gradients of 16 hailstorms are 1 km and 5.66 km respectively; Most cloud anvil echoes are between 1:1 and 3. The above analysis results provide an analysis basis for the monitoring and early warning of hail weather in Jiangxi.
In order to better carry out the monitoring and early warning of hail weather in Jiangxi, MICAPS weather map, Jiangxi meteorological automatic station data, Jiangxi radar mosaic data, single radar PUP product data, double multi wind field data inversion, strong echo automatic recognition, hail disaster photos and WeChat feedback video and other data are used, and the principles and methods of synoptic, radar meteorology, image recognition technology, etc. are adopted, The echo characteristics of hail in Jiangxi and surrounding provinces on March 14, 2022 are analyzed. The results show that: ① On March 14, hail occurred in many places in Jiangxi, strong wind ≥ 17.2 m/s appeared in 20 regional stations, precipitation ≥ 50.0 mm appeared in 24 regional stations, and thunderstorm strong wind and cold air strong wind mixed. ② 200 hPa high-altitude outflow area, 500 hPa south branch and wind shear, 850 hPa low vortex and shear line, ground convergence line and southwest inverted trough are obvious features of weather background; The higher CAPE value in Nanchang, the stronger inversion layer, the middle layer dry area and the lower layer wet area provide the environmental conditions for hail weather. ③ Hail is dominated by supercell echo, sometimes isolated, sometimes in echo group and echo band; Echo intensity ≥ 60 dBz and ≥ 70 dBz; Strong echo area: minimum ≥ 18 km2, maximum ≥ 180 km2; 30-60 dBz range strong echo gradient ≤ 6 km, with obvious cloud anvil echo structure; The life history of hail echo is more than 2 hours. ④ In hail echo recognition, vertical integration of liquid water content VIL is a very important feature. The VIL of Jiangxi hail single radar is 35 ～ 65 kg/m2, and the VIL on the radar puzzle is ≥ 35 kg/m2. ⑤ On the CAPPI chart of 2.5 km hail echo, the hail echo intensity is ≥ 60 dBz, and the maximum is 65 dBz; Most echo centers on double multi wind fields have the characteristics of middle vortex structure, side convergence wind field, north south wind field convergence, etc; Some wind farms are messy. ⑥ Scatter contour algorithm is adopted for automatic echo edge recognition; In each recognition, the thunderstorm echo group can identify multiple strong echoes at the same time, up to 19; ≥ 60 dBz echo area: minimum 18 km2, maximum 184 km2; Most cases showed echo nuclei of 65 dBz, the strongest being 73 dBz; The minimum and maximum echo gradients of 16 hailstorms are 1 km and 5.66 km respectively; Most cloud anvil echoes are between 1:1 and 3. The above analysis results provide an analysis basis for the monitoring and early warning of hail weather in Jiangxi.
Available online: August 21, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.032201
Abstract:
This study is concerned with a nocturnal convective process from the night of the 24th to the early morning of the 25th Sep., 2017. The meso-β-scale convective system on the south side of the frontal rainband perpendicular to the quasi-east-west frontal orientation gradually evolved into a bow echo, which caused short-term heavy precipitation in the middle and lower reaches of the Yangtze River, accompanied by category 7 thunderstorm gale. From the point of view of the large-scale environment, there seem no favorable thermal conditions at night. Therefore it is difficult to make a forecast. Observations and numerical simulations are used to analyze the mechanism. The radar observations show that there is a northeast-southwest meso-β-scale convective belt, moving in the south-easterly direction, and there are new convective cells being triggered on its southwest side, which is called lateral back-building propagation. The new cells then merge into the main convective zone. Another new cell, triggering ahead (southeast side) of the main convective zone, gradually develops into a northwest-southeast belt and moves to the northeast, eventually leads to the original main northeast-southwest convective belt gradually strengthening and finally forming a bow echo. Although the high-resolution numerical model simulation results deviate from observations in intensity and time, the convective system evolution processes are very close to the observations. Therefore, the vertical vorticity equation is used to diagnose the mechanism. The results show that the vorticity tilt term plays an important role in the lateral back-building propagation. In the early stage of the convection development, new cells generate on the southwest side under the effect of the vorticity tilt term and merge with the main echo. The divergence term becomes more important while the echoes merge, the positive vorticity of the main echo increases significantly under both the vorticity tilt term and the divergence term. Besides, the vorticity vertical transport term propagates the positive vorticity upward, which is beneficial to the vertical extension of the main convection. New cells are triggered in front of the main echo due to the effect of the vorticity horizontal advection term. However, the vertical extension height is low, it moves northeastward guided by the low-level wind. Its vorticity increases during the movement and it aligns into a northwest-southeast band, which finally leads to the conversion of the linear main echo into the bow echo. The formation of this bow echo differs significantly from the classical model which has the rear inflow jets in the rear part of the bow echo. On the contrary, this case is mainly influenced by the development of convective systems within the warm zone and has a significant frontal near-surface inflow.
This study is concerned with a nocturnal convective process from the night of the 24th to the early morning of the 25th Sep., 2017. The meso-β-scale convective system on the south side of the frontal rainband perpendicular to the quasi-east-west frontal orientation gradually evolved into a bow echo, which caused short-term heavy precipitation in the middle and lower reaches of the Yangtze River, accompanied by category 7 thunderstorm gale. From the point of view of the large-scale environment, there seem no favorable thermal conditions at night. Therefore it is difficult to make a forecast. Observations and numerical simulations are used to analyze the mechanism. The radar observations show that there is a northeast-southwest meso-β-scale convective belt, moving in the south-easterly direction, and there are new convective cells being triggered on its southwest side, which is called lateral back-building propagation. The new cells then merge into the main convective zone. Another new cell, triggering ahead (southeast side) of the main convective zone, gradually develops into a northwest-southeast belt and moves to the northeast, eventually leads to the original main northeast-southwest convective belt gradually strengthening and finally forming a bow echo. Although the high-resolution numerical model simulation results deviate from observations in intensity and time, the convective system evolution processes are very close to the observations. Therefore, the vertical vorticity equation is used to diagnose the mechanism. The results show that the vorticity tilt term plays an important role in the lateral back-building propagation. In the early stage of the convection development, new cells generate on the southwest side under the effect of the vorticity tilt term and merge with the main echo. The divergence term becomes more important while the echoes merge, the positive vorticity of the main echo increases significantly under both the vorticity tilt term and the divergence term. Besides, the vorticity vertical transport term propagates the positive vorticity upward, which is beneficial to the vertical extension of the main convection. New cells are triggered in front of the main echo due to the effect of the vorticity horizontal advection term. However, the vertical extension height is low, it moves northeastward guided by the low-level wind. Its vorticity increases during the movement and it aligns into a northwest-southeast band, which finally leads to the conversion of the linear main echo into the bow echo. The formation of this bow echo differs significantly from the classical model which has the rear inflow jets in the rear part of the bow echo. On the contrary, this case is mainly influenced by the development of convective systems within the warm zone and has a significant frontal near-surface inflow.
Available online: August 07, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.080301
Abstract:
Radar networking method is one of the most important methods in radar applications. Improving the efficiency of the radar networking method, not only can improve the timeliness of the short-term algorithm sequence, but also can apply high-resolution radar data, which has important practical significance. With the development of GPU(Graphics Processing Unit) general computing interface, GPU has also been regarded as a powerful computing resource rather than display device for rendering and images. Therefore, this study proposes a new GPU parallel radar networking method based on CUDA(Compute Unified Device Architecture). The method is designed in a hybrid architecture of CPU(Central Processing Unit) and GPU, in which the CPU is for the decoding of radar data and scheduling the GPU parallel modules, and the GPU is for the parallel computing of large-scale data. By analyzing the parallel overhead of the CUDA and the characteristics of the radar networking method, a scheme of GPU memory management optimization and data exchange process simplification is proposed and implemented, which effectively improves the efficiency of the method. The comparative test results show that, compared with the CPU parallel algorithm in SWAN(Severe Weather Automatic Nowcasting), the GPU parallel networking method based on CUDA achieves a speed-up ratio of 3.52 and 6.82, respectively, on the national puzzle tasks of 1km and 500m resolution. To sum up, the parallel networking method based on CUDA can not only improve the timeliness of the short-term nowcasting methods sequence, but also provide technical support for the puzzle of higher resolution radar data.
Radar networking method is one of the most important methods in radar applications. Improving the efficiency of the radar networking method, not only can improve the timeliness of the short-term algorithm sequence, but also can apply high-resolution radar data, which has important practical significance. With the development of GPU(Graphics Processing Unit) general computing interface, GPU has also been regarded as a powerful computing resource rather than display device for rendering and images. Therefore, this study proposes a new GPU parallel radar networking method based on CUDA(Compute Unified Device Architecture). The method is designed in a hybrid architecture of CPU(Central Processing Unit) and GPU, in which the CPU is for the decoding of radar data and scheduling the GPU parallel modules, and the GPU is for the parallel computing of large-scale data. By analyzing the parallel overhead of the CUDA and the characteristics of the radar networking method, a scheme of GPU memory management optimization and data exchange process simplification is proposed and implemented, which effectively improves the efficiency of the method. The comparative test results show that, compared with the CPU parallel algorithm in SWAN(Severe Weather Automatic Nowcasting), the GPU parallel networking method based on CUDA achieves a speed-up ratio of 3.52 and 6.82, respectively, on the national puzzle tasks of 1km and 500m resolution. To sum up, the parallel networking method based on CUDA can not only improve the timeliness of the short-term nowcasting methods sequence, but also provide technical support for the puzzle of higher resolution radar data.
Available online: July 31, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.070201
Abstract:
The community of tropical cyclones (TC) researchers has identified intensity change of TC as a high priority study subject. The activity of dry cold air’s air , such as the rapid intensification and rapid weakening is closely related to the intensity change of TC. Domestic and international research results of TC’s intensity change interpreted from the perspective of dry cold air activity is reviewed in the following three parts: the intensity of dry cold air, intrusion location, and upper tropospheric cold weather system’s effects on TC’s intensity change. Also, an outlook for future research is also given here to promote the studies on dry cold air’s effects on the intensity change of TC.
The community of tropical cyclones (TC) researchers has identified intensity change of TC as a high priority study subject. The activity of dry cold air’s air , such as the rapid intensification and rapid weakening is closely related to the intensity change of TC. Domestic and international research results of TC’s intensity change interpreted from the perspective of dry cold air activity is reviewed in the following three parts: the intensity of dry cold air, intrusion location, and upper tropospheric cold weather system’s effects on TC’s intensity change. Also, an outlook for future research is also given here to promote the studies on dry cold air’s effects on the intensity change of TC.
Available online: July 24, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.032002
Abstract:
A laser optical disdrometer (HY-P1000) and a two-dimensional video disdrometer (2DVD) were used to measure the raindrop size distribution (DSD) in Longmen, Xinfeng and Fogang located at Guangdong Province. At the same place and the same time, differences of HY-P1000 and 2DVD on DSD and the accuracy of precipitation retrieval were analyzed. The estimators used for quantitative precipitation estimation (QPE) algorithm were fitted by the disdrometer data collected during 2018 and 2019, and then the optimization rainfall algorithm (HCA-QPE) based on the relations above was applied to Guangzhou S-band dual polarization weather radar to improve the accuracy of QPE in Guangdong. The results showed that: 1) the 2DVD was more sensitive to small drops (<1 mm) while the HY-P1000 appeared to measure much more rain drops larger than 3.5 mm; 2) The polarization parameters retrieved from two types of disdrometers were different from those observed by S band dual-polarization radar at 0.5 ° elevation, and the difference of differential reflectivity was relatively large; 3) What’s more, Using 2DVD observation data can improve the QPE accuracy of S-band dual polarization radar, especially on light rain to moderate rainfall.
A laser optical disdrometer (HY-P1000) and a two-dimensional video disdrometer (2DVD) were used to measure the raindrop size distribution (DSD) in Longmen, Xinfeng and Fogang located at Guangdong Province. At the same place and the same time, differences of HY-P1000 and 2DVD on DSD and the accuracy of precipitation retrieval were analyzed. The estimators used for quantitative precipitation estimation (QPE) algorithm were fitted by the disdrometer data collected during 2018 and 2019, and then the optimization rainfall algorithm (HCA-QPE) based on the relations above was applied to Guangzhou S-band dual polarization weather radar to improve the accuracy of QPE in Guangdong. The results showed that: 1) the 2DVD was more sensitive to small drops (<1 mm) while the HY-P1000 appeared to measure much more rain drops larger than 3.5 mm; 2) The polarization parameters retrieved from two types of disdrometers were different from those observed by S band dual-polarization radar at 0.5 ° elevation, and the difference of differential reflectivity was relatively large; 3) What’s more, Using 2DVD observation data can improve the QPE accuracy of S-band dual polarization radar, especially on light rain to moderate rainfall.
Available online: July 21, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.071901
Abstract:
The mountain-valley circulation is a local circulation driven by thermal difference. Wuyishan is surrounded by mountains on three sides and the center is a hilly area, making the mountain-valley circulation prevalent throughout the year. Based on the ground weather observation station, boundary wind-detecting lidar, and ADM-Aeolus (Atmospheric Dynamics Mission Aeolus) lidar satellite data, this study studied the characteristics of mountain-valley circulation in Wuyishan. The results show that 1) the valley wind days are the most in summer; 2) the atmospheric diurnal variation characteristics of the valley wind days are significant: In the mountain wind stage, the primary wind is northerly, the wind speed is small, the low-altitude radar signal-noise ratio is strong, and air movement is mainly sinking; The valley wind stage is dominated by the southerly wind, which is stronger than the mountain wind stage, and the low-altitude radar echo signal is weakened, and the updraft is dominated; 3) When the mountain wind prevails, the wind forms a circulation circle in the vertical direction; 4) According to the wind profile of the lidar data fusion, it is pointed out that the non-valley wind day occurs under the weather situation where southerly wind prevails in the middle and lower layers of the convection. The southerly wind transports water vapor to the local area, causing the local low altitude to be covered by thicker clouds or precipitation, which weakens the thermal difference between mountains and valleys, and the earth circulation is broken.
The mountain-valley circulation is a local circulation driven by thermal difference. Wuyishan is surrounded by mountains on three sides and the center is a hilly area, making the mountain-valley circulation prevalent throughout the year. Based on the ground weather observation station, boundary wind-detecting lidar, and ADM-Aeolus (Atmospheric Dynamics Mission Aeolus) lidar satellite data, this study studied the characteristics of mountain-valley circulation in Wuyishan. The results show that 1) the valley wind days are the most in summer; 2) the atmospheric diurnal variation characteristics of the valley wind days are significant: In the mountain wind stage, the primary wind is northerly, the wind speed is small, the low-altitude radar signal-noise ratio is strong, and air movement is mainly sinking; The valley wind stage is dominated by the southerly wind, which is stronger than the mountain wind stage, and the low-altitude radar echo signal is weakened, and the updraft is dominated; 3) When the mountain wind prevails, the wind forms a circulation circle in the vertical direction; 4) According to the wind profile of the lidar data fusion, it is pointed out that the non-valley wind day occurs under the weather situation where southerly wind prevails in the middle and lower layers of the convection. The southerly wind transports water vapor to the local area, causing the local low altitude to be covered by thicker clouds or precipitation, which weakens the thermal difference between mountains and valleys, and the earth circulation is broken.
Available online: June 30, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.052801
Abstract:
Wind farms have obvious impact on the local climate. However, whether obvious differences on environmental effects of local wind between the inland and offshore wind farms still need to be explored. This article used the inland wind farms data from Shangyi, Hebei province and offshore wind farms in Rudong, Jiangsu province. Based on the data of meteorological observation and wind gradient tower around wind farm, the influence and comparative analysis on the inland and offshore wind farms on local wind environment, Turbulence Intensity (TI) and Wind Shear Exponent(WSE) were preliminarily analyzed. The results showed that the inland and offshore wind farms have significant effects on TI and WSE. The construction of inland and offshore wind farms has an enhancement effect on TI. The average annual TI increased by 31% and 37%, and the largest rise occurred in spring (47%) and winter (49%) in inland and offshore wind farms respectively. Moreover, the TI increasing range of high-level was greater than that in low-level, and greater at night than in day in inland wind. The TI increasing range was relatively smooth of different heights and diurnal variation in offshore wind farms. The construction of inland and offshore wind farms has significant differences effect on WSE. The WSE increased during the day and decreased at night, and the daily variation was significantly reduced and the average annual WSE decreased by 8%, the largest decline of WSE occurred in autumn (12%) at inland wind farms. The WSE increased obviously during the day and night with average annual WSE increased by 24%, and the largest rise occurred in spring (37%) at offshore wind farms .
Wind farms have obvious impact on the local climate. However, whether obvious differences on environmental effects of local wind between the inland and offshore wind farms still need to be explored. This article used the inland wind farms data from Shangyi, Hebei province and offshore wind farms in Rudong, Jiangsu province. Based on the data of meteorological observation and wind gradient tower around wind farm, the influence and comparative analysis on the inland and offshore wind farms on local wind environment, Turbulence Intensity (TI) and Wind Shear Exponent(WSE) were preliminarily analyzed. The results showed that the inland and offshore wind farms have significant effects on TI and WSE. The construction of inland and offshore wind farms has an enhancement effect on TI. The average annual TI increased by 31% and 37%, and the largest rise occurred in spring (47%) and winter (49%) in inland and offshore wind farms respectively. Moreover, the TI increasing range of high-level was greater than that in low-level, and greater at night than in day in inland wind. The TI increasing range was relatively smooth of different heights and diurnal variation in offshore wind farms. The construction of inland and offshore wind farms has significant differences effect on WSE. The WSE increased during the day and decreased at night, and the daily variation was significantly reduced and the average annual WSE decreased by 8%, the largest decline of WSE occurred in autumn (12%) at inland wind farms. The WSE increased obviously during the day and night with average annual WSE increased by 24%, and the largest rise occurred in spring (37%) at offshore wind farms .
HOU Shumei, Zhu Xiqoqing, Shi qian, TANG Qiaoling, MENG Xiangui, LIU Chang, GAO Rongzhen, DIAO Xiuguang
Available online: June 30, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.053101
Abstract:
A large-scale extremely severe convective weather named “5.17” severe convection occurred in Shandong Province on May 17, 2020, the hail coverage is the 10-year largest. Convective storms were highly organized, the regional supercell clusters and a strong squall line over 500km in length caused this extremely severe convection. Based on ERA5 reanalysis, encrypted automatic meteorological observation station, Doppler weather radar data, the environmental conditions of this extremely severe convective weather are analyzed. The results show that: (1) The cold vortex was located in the key area which is most conducive to Shandong severe convection，the large-scale weather system forcing was strong, and the unusually strong cold air in the middle troposphere moved southward to affect the previously abnormally warm Shandong Province, resulting in the "5.17" extremely severe convection weather. (2) The anomaly of weather system is more representative of the intensity of dynamic and thermal forcing，with an anomaly level above 2σ the extremely severe convection would be caused. When the intensity of the cold vortex weakened during its southward moving, but the degree of anomaly was increasing, it may still cause extremely severe convective weather in its southeast quadrant. (3) The strong deep vertical wind shear was conducive to storms organization, the long axis of the squall line orientated the same direction as the 0-6km vertical wind shear vector. The area where new cells initiated, developed and merged was located in the front of the large value center of the wind vector difference. (4) The low-level warm and moist advection continuously transported warm and humid air to Shandong, which was the mechanism of CAPE reconstruction and the main energy source for the long-term maintenance of supercell groups and long squall lines.
A large-scale extremely severe convective weather named “5.17” severe convection occurred in Shandong Province on May 17, 2020, the hail coverage is the 10-year largest. Convective storms were highly organized, the regional supercell clusters and a strong squall line over 500km in length caused this extremely severe convection. Based on ERA5 reanalysis, encrypted automatic meteorological observation station, Doppler weather radar data, the environmental conditions of this extremely severe convective weather are analyzed. The results show that: (1) The cold vortex was located in the key area which is most conducive to Shandong severe convection，the large-scale weather system forcing was strong, and the unusually strong cold air in the middle troposphere moved southward to affect the previously abnormally warm Shandong Province, resulting in the "5.17" extremely severe convection weather. (2) The anomaly of weather system is more representative of the intensity of dynamic and thermal forcing，with an anomaly level above 2σ the extremely severe convection would be caused. When the intensity of the cold vortex weakened during its southward moving, but the degree of anomaly was increasing, it may still cause extremely severe convective weather in its southeast quadrant. (3) The strong deep vertical wind shear was conducive to storms organization, the long axis of the squall line orientated the same direction as the 0-6km vertical wind shear vector. The area where new cells initiated, developed and merged was located in the front of the large value center of the wind vector difference. (4) The low-level warm and moist advection continuously transported warm and humid air to Shandong, which was the mechanism of CAPE reconstruction and the main energy source for the long-term maintenance of supercell groups and long squall lines.
Available online: June 06, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.051602
Abstract:
Abstract: Based on the ERA5 reanalysis data in June from 1979 to 2016 and moist thermodynamic advection parameter, thermal helicity, divergence flux, moisture divergence flux and the thermodynamic wave-activity density as five comprehensive factors were selected by nuclear density estimation to construct the probability prediction model of regional persistent rainstorm in Hunan. Threat Score (TS) method as the test standard to establish the optimal factor and weight combination. The results show that the average TS of independent samples from 2017 to 2019 reaches 29.9, which was a positive skill compared with European Centre for Medium-Range Weather Forecasts fine grid(with an average TS score of 22.4%). During the two regional persistent rainstorm operational experiment in 2021 and 2022 flood season, the rainstorm forecast 24 hours in advance is superior to the ECMWF,CMA-GFS large-scale model and CMA-SH, CMA-GD regional mesoscale model,which has a strong ability to forecast the regional persistent rainstorm in Hunan.
Abstract: Based on the ERA5 reanalysis data in June from 1979 to 2016 and moist thermodynamic advection parameter, thermal helicity, divergence flux, moisture divergence flux and the thermodynamic wave-activity density as five comprehensive factors were selected by nuclear density estimation to construct the probability prediction model of regional persistent rainstorm in Hunan. Threat Score (TS) method as the test standard to establish the optimal factor and weight combination. The results show that the average TS of independent samples from 2017 to 2019 reaches 29.9, which was a positive skill compared with European Centre for Medium-Range Weather Forecasts fine grid(with an average TS score of 22.4%). During the two regional persistent rainstorm operational experiment in 2021 and 2022 flood season, the rainstorm forecast 24 hours in advance is superior to the ECMWF,CMA-GFS large-scale model and CMA-SH, CMA-GD regional mesoscale model,which has a strong ability to forecast the regional persistent rainstorm in Hunan.
Available online: May 29, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.051601
Abstract:
Using hourly precipitation data, conventional meteorological observations, Yinchuan CA radar data and ERA5 high resolution reanalysis data from 2006 to 2021, this paper studies the temporal and spatial correlation between the low-level jet and the rainstorm process in the eastern region of the Helan Mountain, and discusses initially the possible mechanism of low-level jet affecting the occurrence and development of rainstorm. The results show that: (1) The low-level jet is mainly distributed in three key areas, including Hetao South, southeast Ningxia and southwest Shanxi province, which corresponds to south jet at 700 hPa, southerly jet at 775 hPa and southeast jet at 850 hPa respectively; The southeast of Ningxia is a transfer station where three low-level jets merge towards north and west, has an extremely important impact on the occurrence and development of the rainstorm process in the eastern region of Helan Mountain; (2) According to the height of the maximum wind speed axis of the low-level jet, the low-level jet processes affecting the rainstorm process in the eastern region of Helan Mountain are divided into seven types. Among them, the frequency of the three levels jet pattern is the highest, accounting for about 54.5% of the total process, followed by the process with 700 hPa and 775 hPa jet simultaneously (accounting for 36.4%); (3) The rainstorm process is consistent with the low-level jet in time: the establishment of low-level jet at 700, 775 and 850 hPa are 18, 10 and 7 hours earlier averagely than the beginning of rainstorm. The maximum wind speed of low-level jet at 700 hPa and 775 hPa jet stream are 54 and 18 minutes earlier than the maximum rainfall intensity of rainstorm process, while the maximum wind speed of low-level jet at 850 hPa lags 12 min behind the maximum intensity of rainstorm process. The frequencies of 850 hPa Level 1 jet and 775 hPa Level 2 jet are more indicative of the frequency of short-term rainstorm of 20-40 mm·h-1 and 40-60 mm·h-1 respectively, and the average wind speed of low-level jet at 700 hPa in the key area in the south of Hetao is more indicative of the maximum rainfall intensity of the rainstorm process; (4) There is also spatial consistency between rainstorm process and low-level jet: with the low-level jet establishes, strengthens and moves towards north or west, weakens and retreats eastward or southward, the rainstorm starts, intensifies and weakens, and the rainstorm area is located in the left front of the jet axis; (5) Combined with the topography of Helan Mountain, the low-level jet moves northward and westward, triggers multiple convective cells in front of the east slope, merges and strengthens to form a linear echo with slow movement, strong development, highly organized and obvious train effect, which is easy to create local strong convective rainstorm in Helan Mountain area.
Using hourly precipitation data, conventional meteorological observations, Yinchuan CA radar data and ERA5 high resolution reanalysis data from 2006 to 2021, this paper studies the temporal and spatial correlation between the low-level jet and the rainstorm process in the eastern region of the Helan Mountain, and discusses initially the possible mechanism of low-level jet affecting the occurrence and development of rainstorm. The results show that: (1) The low-level jet is mainly distributed in three key areas, including Hetao South, southeast Ningxia and southwest Shanxi province, which corresponds to south jet at 700 hPa, southerly jet at 775 hPa and southeast jet at 850 hPa respectively; The southeast of Ningxia is a transfer station where three low-level jets merge towards north and west, has an extremely important impact on the occurrence and development of the rainstorm process in the eastern region of Helan Mountain; (2) According to the height of the maximum wind speed axis of the low-level jet, the low-level jet processes affecting the rainstorm process in the eastern region of Helan Mountain are divided into seven types. Among them, the frequency of the three levels jet pattern is the highest, accounting for about 54.5% of the total process, followed by the process with 700 hPa and 775 hPa jet simultaneously (accounting for 36.4%); (3) The rainstorm process is consistent with the low-level jet in time: the establishment of low-level jet at 700, 775 and 850 hPa are 18, 10 and 7 hours earlier averagely than the beginning of rainstorm. The maximum wind speed of low-level jet at 700 hPa and 775 hPa jet stream are 54 and 18 minutes earlier than the maximum rainfall intensity of rainstorm process, while the maximum wind speed of low-level jet at 850 hPa lags 12 min behind the maximum intensity of rainstorm process. The frequencies of 850 hPa Level 1 jet and 775 hPa Level 2 jet are more indicative of the frequency of short-term rainstorm of 20-40 mm·h-1 and 40-60 mm·h-1 respectively, and the average wind speed of low-level jet at 700 hPa in the key area in the south of Hetao is more indicative of the maximum rainfall intensity of the rainstorm process; (4) There is also spatial consistency between rainstorm process and low-level jet: with the low-level jet establishes, strengthens and moves towards north or west, weakens and retreats eastward or southward, the rainstorm starts, intensifies and weakens, and the rainstorm area is located in the left front of the jet axis; (5) Combined with the topography of Helan Mountain, the low-level jet moves northward and westward, triggers multiple convective cells in front of the east slope, merges and strengthens to form a linear echo with slow movement, strong development, highly organized and obvious train effect, which is easy to create local strong convective rainstorm in Helan Mountain area.
Available online: May 24, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.052401
Abstract:
PM2.5 and O3 which interact with each other have become the most important pollutants in the cities of FenWei Plain. The pollution often occurs simultaneously in the warm season and is closely related to meteorological conditions. Based on the daily PM2.5 and O3 concentration data, ground meteorological observation data and ERA5 high-altitude re-analysis data of 12 cities in the FenWei Plain from 2015 to 2021, the spatio-temporal characteristics of PM2.5 and O3 in the FenWei Plain, as well as the relationship between PM2.5 and O3 when combined pollution occurs were analyzed, and the impact of local meteorological conditions and synoptic situation on combined pollution is also studied in this paper. The result shows that the average annual PM2.5 and MDA8 O3 (maximum daily 8-h average ozone) concentrations in the FenWei Plain began to decline continuously in 2017 and 2018, respectively, and the number of compound pollution days also began to decline continuously after 2019, due to the implementation of "collaborative pollution control" and "one city, one policy"; The effects of PM2.5 (MDA8 O3) on MDA8 O3 (PM2.5) were analyzed; the increase of PM2.5 can weaken solar radiation which affects O3 generation so that the two are negatively correlated, while O3 will also oxidize secondary particulate matter generation and lead to an increase in PM2.5 concentration, showing a positive correlation between PM2.5 and O3; combined pollution mainly occurs in March-September, frequently in the eastern cities of the FenWei Plain , and mostly in condition of high temperature and low humidity; Finally, the synoptic circulation situation of combined pollution is divided into four types by principal component analysis in the T-mode (T-PCA algorithm), featured by northwest or the westerly air flow in high-altitude and the warm zone southerly wind or breeze in low layer. The results of the study provide the observation basis for controlling pollution in the FenWei Plain and are of great significance for cooperative governance for PM2.5 and O3 pollution especially.
PM2.5 and O3 which interact with each other have become the most important pollutants in the cities of FenWei Plain. The pollution often occurs simultaneously in the warm season and is closely related to meteorological conditions. Based on the daily PM2.5 and O3 concentration data, ground meteorological observation data and ERA5 high-altitude re-analysis data of 12 cities in the FenWei Plain from 2015 to 2021, the spatio-temporal characteristics of PM2.5 and O3 in the FenWei Plain, as well as the relationship between PM2.5 and O3 when combined pollution occurs were analyzed, and the impact of local meteorological conditions and synoptic situation on combined pollution is also studied in this paper. The result shows that the average annual PM2.5 and MDA8 O3 (maximum daily 8-h average ozone) concentrations in the FenWei Plain began to decline continuously in 2017 and 2018, respectively, and the number of compound pollution days also began to decline continuously after 2019, due to the implementation of "collaborative pollution control" and "one city, one policy"; The effects of PM2.5 (MDA8 O3) on MDA8 O3 (PM2.5) were analyzed; the increase of PM2.5 can weaken solar radiation which affects O3 generation so that the two are negatively correlated, while O3 will also oxidize secondary particulate matter generation and lead to an increase in PM2.5 concentration, showing a positive correlation between PM2.5 and O3; combined pollution mainly occurs in March-September, frequently in the eastern cities of the FenWei Plain , and mostly in condition of high temperature and low humidity; Finally, the synoptic circulation situation of combined pollution is divided into four types by principal component analysis in the T-mode (T-PCA algorithm), featured by northwest or the westerly air flow in high-altitude and the warm zone southerly wind or breeze in low layer. The results of the study provide the observation basis for controlling pollution in the FenWei Plain and are of great significance for cooperative governance for PM2.5 and O3 pollution especially.
Available online: April 26, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.021502
Abstract:
The accuracy of MWR measurements obtained at Baoshan Station of Shanghai from July 2018 to July 2019 are evaluated by comparing brightness temperature of MWR against those calculated from radiosonde soundings at the same site with radiative transfer model. Beyond that, the performances of the MWR calibrations techniques and the effects of radome replacement are estimated. Results show that the observed brightness temperature from MWR agrees well with the simulated ones of radiosonde soundings in clear-sky conditions. The correlation coefficients between two datasets are over 0.96 in all channels, with root mean square errors 0.15-2.68 K. The performances of the V band channels are better than those of K band channels. Moreover, the features of brightness temperature bias vary with channels, including systematic biases, random deviations and biases with significant seasonal variations. The LN2 calibration could significantly reduce the systematic drifts in most of K-band channels. But the brightness temperature from V-band channels do not change obviously after LN2 calibration. By replacing the radome periodically, brightness temperature biases in the rainy conditions might be reduced significantly. And the recovery time of brightness temperature might also be shortened. Results also indicate that the radome made of new material used in this study is more efficient than the original one in reducing the negative impacts of precipitation in MWR accuracy. It works for about 4 months.
The accuracy of MWR measurements obtained at Baoshan Station of Shanghai from July 2018 to July 2019 are evaluated by comparing brightness temperature of MWR against those calculated from radiosonde soundings at the same site with radiative transfer model. Beyond that, the performances of the MWR calibrations techniques and the effects of radome replacement are estimated. Results show that the observed brightness temperature from MWR agrees well with the simulated ones of radiosonde soundings in clear-sky conditions. The correlation coefficients between two datasets are over 0.96 in all channels, with root mean square errors 0.15-2.68 K. The performances of the V band channels are better than those of K band channels. Moreover, the features of brightness temperature bias vary with channels, including systematic biases, random deviations and biases with significant seasonal variations. The LN2 calibration could significantly reduce the systematic drifts in most of K-band channels. But the brightness temperature from V-band channels do not change obviously after LN2 calibration. By replacing the radome periodically, brightness temperature biases in the rainy conditions might be reduced significantly. And the recovery time of brightness temperature might also be shortened. Results also indicate that the radome made of new material used in this study is more efficient than the original one in reducing the negative impacts of precipitation in MWR accuracy. It works for about 4 months.
Available online: March 27, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.032601
Abstract:
A climatology is developed for tornadoes during 1971–2020 in Liaoning. Tornado reports are from the "Chinese Meteorological Disaster Dictionary", "Chinese Meteorological Disaster Yearbook" and other related data. The climatology includes interannual variability, annual and diurnal cycles, intensities according to the “Enhanced Fujita Scale”, geographic distribution, and environmental conditions derived from model analysis data. Given the study results, (1) Over the 50 years, there were 105 tornadoes recorded(Including 17 tornadoes above EF2) in 97 tornadic days with a mean of 2.1 tornadoes annually and 0.14 tornadoes per year per 10000 km2,about 1/10 of the United States. Tornadoes occurred with a maximum(95%) from May through September. 67% of tornadoes genesises in the diurnal variation are between 14:00 BT and 19:00 BT. Significant tornadoes mainly occur in the central and west Liaoning, and more of the tornadoes occur in southeastern coastal area weak tornadoes. The tornadic season in the northwest of Liaoning is significantly earlier than the southeast.(2)CAPE and mid-level wind shear is inversely phase changes with the seasons, which makes the appropriate configuration of the two be prerequisites. The lower low-level storm relative helicity in climate state is the main reason for the apparently lower tornado density in Liaoning than in the United States.(3)87% of tornadoes are related to cold vortex, which are mainly divided into short wave trough category at cold vortex bottom and cold vortex front category dominated by low-level frontogenesis (65%) , mid-level dry cold air forcing category dominated by mid-to-high level dry cold air flow(12%), and the cold vortex central area category dominated by meso-scale near-storm environment under severe thermal instability (6%). The characteristic field of typical tornadoes in Liaoning shows that: the comprehensive configurations of cold vortex at middle-level; high wind speed core and relative storm helicity at low-level; CAPE gradient large value area; cold front, warm temperature ridge, and dry line at surface are important indications for tornado-prone areas in Liaoning.(4)The environmental conditions in the high-incidence area of Liaoning tornadoes have the following characteristics:the mid-level system is cold vortex, the ground corresponds to frontal cyclones, tornadoes often appear in the northwest quadrant of the center of SRH, and in the large value area of CAPE gradient, corresponding to the front side of the ground cold front1 ~2.5 latitudes, the top of the temperature ridge, and 1~1.5 latitudes on the east side of the dry line.
A climatology is developed for tornadoes during 1971–2020 in Liaoning. Tornado reports are from the "Chinese Meteorological Disaster Dictionary", "Chinese Meteorological Disaster Yearbook" and other related data. The climatology includes interannual variability, annual and diurnal cycles, intensities according to the “Enhanced Fujita Scale”, geographic distribution, and environmental conditions derived from model analysis data. Given the study results, (1) Over the 50 years, there were 105 tornadoes recorded(Including 17 tornadoes above EF2) in 97 tornadic days with a mean of 2.1 tornadoes annually and 0.14 tornadoes per year per 10000 km2,about 1/10 of the United States. Tornadoes occurred with a maximum(95%) from May through September. 67% of tornadoes genesises in the diurnal variation are between 14:00 BT and 19:00 BT. Significant tornadoes mainly occur in the central and west Liaoning, and more of the tornadoes occur in southeastern coastal area weak tornadoes. The tornadic season in the northwest of Liaoning is significantly earlier than the southeast.(2)CAPE and mid-level wind shear is inversely phase changes with the seasons, which makes the appropriate configuration of the two be prerequisites. The lower low-level storm relative helicity in climate state is the main reason for the apparently lower tornado density in Liaoning than in the United States.(3)87% of tornadoes are related to cold vortex, which are mainly divided into short wave trough category at cold vortex bottom and cold vortex front category dominated by low-level frontogenesis (65%) , mid-level dry cold air forcing category dominated by mid-to-high level dry cold air flow(12%), and the cold vortex central area category dominated by meso-scale near-storm environment under severe thermal instability (6%). The characteristic field of typical tornadoes in Liaoning shows that: the comprehensive configurations of cold vortex at middle-level; high wind speed core and relative storm helicity at low-level; CAPE gradient large value area; cold front, warm temperature ridge, and dry line at surface are important indications for tornado-prone areas in Liaoning.(4)The environmental conditions in the high-incidence area of Liaoning tornadoes have the following characteristics:the mid-level system is cold vortex, the ground corresponds to frontal cyclones, tornadoes often appear in the northwest quadrant of the center of SRH, and in the large value area of CAPE gradient, corresponding to the front side of the ground cold front1 ~2.5 latitudes, the top of the temperature ridge, and 1~1.5 latitudes on the east side of the dry line.
Available online: March 21, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.010901
Abstract:
Coastal offshore observation stations are rare, while coastal land observation stations are relatively dense. Carrying out research on the characteristics of land-sea wind speed difference caused by land-sea distribution and realizing the estimation of sea surface wind speed from land observation wind speed is helpful to improve the service ability of sea surface wind forecast. In this paper, the hourly mean wind speed and gust speed data of two groups of buoys and their adjacent land observation stations in the north coast of China from 2016 to 2020 are used to statistically analyze the characteristics and regularity of the difference between sea surface wind speed and land wind speed. And the support vector machine method is used to build the sea surface wind speed estimation model based on the land mean wind speed, land gust speed, distance between land-sea stations, month and hour. The estimation model is tested by using the observation data of the other two groups of land-sea observation stations in 2021. The results show that for the mean wind speed above scale 5 and gust wind speed above scale 6, the model has a high estimation accuracy and is superior to ERA5. The root mean square error of the mean wind speed (gust speed) of the two groups estimated by the model is 2.40 m·s-1 (3.20 m·s-1) and 2.35 m·s-1 (3.20 m·s-1 and 2.57 m·s-1), respectively. Compared with ERA5, it decreased by 24% (14%) and 23% (14% and 20%) respectively. In a strong wind process jointly affected by an extratropical cyclone and cold air, the mean absolute errors of the mean wind speed (gust speed) estimated by the model for the two test groups are 1.6 m·s-1 (2.3 m·s-1) and 1.1 m·s-1 (2.3 m·s-1 and 1.5 m·s-1) respectively, and the mean wind speed (gust speed) errors at the extreme moment are -1.3 m·s-1 (-0.6 m·s-1) and -1.2 m·s-1 (-0.6 m·s-1 and -3.1 m·s-1) respectively, which are better than that of ERA5. The sea surface wind speed estimation model based on support vector machine can estimate accurate heavy sea surface wind speed using the land observation wind speed, which can reduce the impact of insufficient sea observation data, and has a certain application prospect.
Coastal offshore observation stations are rare, while coastal land observation stations are relatively dense. Carrying out research on the characteristics of land-sea wind speed difference caused by land-sea distribution and realizing the estimation of sea surface wind speed from land observation wind speed is helpful to improve the service ability of sea surface wind forecast. In this paper, the hourly mean wind speed and gust speed data of two groups of buoys and their adjacent land observation stations in the north coast of China from 2016 to 2020 are used to statistically analyze the characteristics and regularity of the difference between sea surface wind speed and land wind speed. And the support vector machine method is used to build the sea surface wind speed estimation model based on the land mean wind speed, land gust speed, distance between land-sea stations, month and hour. The estimation model is tested by using the observation data of the other two groups of land-sea observation stations in 2021. The results show that for the mean wind speed above scale 5 and gust wind speed above scale 6, the model has a high estimation accuracy and is superior to ERA5. The root mean square error of the mean wind speed (gust speed) of the two groups estimated by the model is 2.40 m·s-1 (3.20 m·s-1) and 2.35 m·s-1 (3.20 m·s-1 and 2.57 m·s-1), respectively. Compared with ERA5, it decreased by 24% (14%) and 23% (14% and 20%) respectively. In a strong wind process jointly affected by an extratropical cyclone and cold air, the mean absolute errors of the mean wind speed (gust speed) estimated by the model for the two test groups are 1.6 m·s-1 (2.3 m·s-1) and 1.1 m·s-1 (2.3 m·s-1 and 1.5 m·s-1) respectively, and the mean wind speed (gust speed) errors at the extreme moment are -1.3 m·s-1 (-0.6 m·s-1) and -1.2 m·s-1 (-0.6 m·s-1 and -3.1 m·s-1) respectively, which are better than that of ERA5. The sea surface wind speed estimation model based on support vector machine can estimate accurate heavy sea surface wind speed using the land observation wind speed, which can reduce the impact of insufficient sea observation data, and has a certain application prospect.
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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．
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
2007,33(12):116-120, DOI: 10.7519/j.issn.1000-0526.2007.12.018
Abstract:
A comprehensive analysis and process system based on ArcGIS, and its chief targ et, its software frame, standardized data, database system, basic functions and its key technique, etc. are are described. The system is professional especially to weather modification, and it mainly applies to comprehensive analysis and pr ocess for weather modification, decision-making of operation schemes, appraisal of operation effectiveness, and services for enhancement precipitation or suppre ssion hail by ways of cannons or rocks, etc. In this system, information collect ion, analysis, management and comprehensive application of the weather modificat ion are realized. It also can be used in other fields in meteorology.
A comprehensive analysis and process system based on ArcGIS, and its chief targ et, its software frame, standardized data, database system, basic functions and its key technique, etc. are are described. The system is professional especially to weather modification, and it mainly applies to comprehensive analysis and pr ocess for weather modification, decision-making of operation schemes, appraisal of operation effectiveness, and services for enhancement precipitation or suppre ssion hail by ways of cannons or rocks, etc. In this system, information collect ion, analysis, management and comprehensive application of the weather modificat ion are realized. It also can be used in other fields in meteorology.
2011,37(1):122-128, DOI: 10.7519/j.issn.1000-0526.2011.1.017
Abstract:
The following are the main characteristics of the general atmospheric circulation in October 2010. There were two polar vortex centers in the Northern Hemisphere. The circulation presents a four wave pattern in middle high latitudes, in which the strong Ural ridge corresponds to a large 40 gpm positive anomaly area. Strength of the Western Pacific subtropical high is weaker than normal years. The monthly mean temperature (10.1 ℃) is 0.5 ℃ higher than the same period of normal years, and the mean precipitation (42.6 mm) is 15.1% above normal. The major weather events include: 8 precipitation processes occuring, in which a rare heavy rain has struck on Hainan in the first and middle dekad of October; two tropical cyclones generated, with one super typhoon (Chaba, numbered 1013) landed in Fujian; in the last dekad of October, strong cold air outbreak across most areas of China; heavy fog aroused in the central and eastern China.
The following are the main characteristics of the general atmospheric circulation in October 2010. There were two polar vortex centers in the Northern Hemisphere. The circulation presents a four wave pattern in middle high latitudes, in which the strong Ural ridge corresponds to a large 40 gpm positive anomaly area. Strength of the Western Pacific subtropical high is weaker than normal years. The monthly mean temperature (10.1 ℃) is 0.5 ℃ higher than the same period of normal years, and the mean precipitation (42.6 mm) is 15.1% above normal. The major weather events include: 8 precipitation processes occuring, in which a rare heavy rain has struck on Hainan in the first and middle dekad of October; two tropical cyclones generated, with one super typhoon (Chaba, numbered 1013) landed in Fujian; in the last dekad of October, strong cold air outbreak across most areas of China; heavy fog aroused in the central and eastern China.
2013,39(9):1163-1170, DOI: 10.7519/j.issn.1000-0526.2013.09.011
Abstract:
Drought and flood have significant impacts on catchment water use and ecological balance. To develop practical drought/flood monitoring indicators that only need a few climate variables, it is fundamentally necessary to explore the relationship between hydrology variables and climate variables for the specific catchment. This study investigates the correlations between lake water level and various time scale climatological indices according to the standardized precipitation index (SPI) and the standardized precipitation evapotranspiration index (SPEI), based on the monthly water level records from Honghu Lake representative gauging stations and the monthly observations of 8 meteorological stations in the Four Lake Basin. The results showed that extreme droughts and floods are primarily controlled by precipitation variability over the Four Lake Basin, and both SPEI and SPI are well related with lake water level of Honghu Lake while the degree of the correlation varies between different seasons and SPEI/SPI time scales, with the highest correlations for rainy summer and autumn months. Generally, the 4-6 month scale SPEI/SPI drought index is most closely correlated with lake water level of Honghu Lake, showing an apparent response of lake water level to the current and former months’ water surplus and deficiency. When compared with the historical time series of monthly average lake water level of Honghu Lake, the 5 month scale SPEI/SPI agrees well with the variability of the lake water level. The response relationship found during the study can not only aid the monitoring and forecasting of flood and drought conditions in the Four Lake Basin based on conventional weather data, but also provides some references for other places of China.
Drought and flood have significant impacts on catchment water use and ecological balance. To develop practical drought/flood monitoring indicators that only need a few climate variables, it is fundamentally necessary to explore the relationship between hydrology variables and climate variables for the specific catchment. This study investigates the correlations between lake water level and various time scale climatological indices according to the standardized precipitation index (SPI) and the standardized precipitation evapotranspiration index (SPEI), based on the monthly water level records from Honghu Lake representative gauging stations and the monthly observations of 8 meteorological stations in the Four Lake Basin. The results showed that extreme droughts and floods are primarily controlled by precipitation variability over the Four Lake Basin, and both SPEI and SPI are well related with lake water level of Honghu Lake while the degree of the correlation varies between different seasons and SPEI/SPI time scales, with the highest correlations for rainy summer and autumn months. Generally, the 4-6 month scale SPEI/SPI drought index is most closely correlated with lake water level of Honghu Lake, showing an apparent response of lake water level to the current and former months’ water surplus and deficiency. When compared with the historical time series of monthly average lake water level of Honghu Lake, the 5 month scale SPEI/SPI agrees well with the variability of the lake water level. The response relationship found during the study can not only aid the monitoring and forecasting of flood and drought conditions in the Four Lake Basin based on conventional weather data, but also provides some references for other places of China.
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.
2013,39(3):281-290, DOI: 10.7519/j.issn.1000-0526.2013.03.002
Abstract:
By using conventional observation data and NCEP reanalysis data, diagnostic analysis is performed on a rainstorm process, which occurred on 22-25 July 2010 in the western part of Sichuan Basin. The result shows that the rainstorm was generated under the circulation background that low level southerly airflows had remained over the region from the South China Sea to Sichuan Basin, so this rainstorm was closely related to the evolution of the southerly wind speeds. The rainfall intensity increased as the south winds grew stronger. Speed convergence formed by the enhanced south winds and positive vorticity advections became main dynamic trigger factors for the rainstorm. Therefore, the rainstorm is pretty consistent with the low level convergence and the positive vorticity advection. In addition, the result of WRF numerical simulation further indicates that: the evolution of 3 h wind speed at 850 hPa has good indication for the development of mesoscale convective systems. On the leeward side of the 3 h wind speed increasing area, convective cloud clusters are to develop rapidly in the next 3 hours. Moreover, the topographic influence simulation tests suggest that the airflow convergence generated in the west of the Basin is closely related to the topography of plateau.
By using conventional observation data and NCEP reanalysis data, diagnostic analysis is performed on a rainstorm process, which occurred on 22-25 July 2010 in the western part of Sichuan Basin. The result shows that the rainstorm was generated under the circulation background that low level southerly airflows had remained over the region from the South China Sea to Sichuan Basin, so this rainstorm was closely related to the evolution of the southerly wind speeds. The rainfall intensity increased as the south winds grew stronger. Speed convergence formed by the enhanced south winds and positive vorticity advections became main dynamic trigger factors for the rainstorm. Therefore, the rainstorm is pretty consistent with the low level convergence and the positive vorticity advection. In addition, the result of WRF numerical simulation further indicates that: the evolution of 3 h wind speed at 850 hPa has good indication for the development of mesoscale convective systems. On the leeward side of the 3 h wind speed increasing area, convective cloud clusters are to develop rapidly in the next 3 hours. Moreover, the topographic influence simulation tests suggest that the airflow convergence generated in the west of the Basin is closely related to the topography of plateau.
2011,37(2):142-155, DOI: 10.7519/j.issn.1000-0526.2011.2.003
Abstract:
Using the Variational Doppler Radar Analysis System (VDRAS) combined with local unconventional observation data, a more in depth contrastive analysis is carried on the initiation mechanism of two storm cases in Beijing, one is 814 (August 14, 2008) case with strong rainfall that we call it as moist storm and the other is 824 (August 24, 2008) case with little rainfall that we call it as dry storm. The results show: (1) The synoptic scale systems of 814 storm were stable Northeast cold vortex low trough at 500 hPa and shear line at 850 hPa, the specific humidity that more than 12 g·kg-1 below 850 hPa and the relative humidity that more than 90% in the surface indicated that the atmosphere was very moist. It had convective instability caused by humidity advection in lower levels. The 824 storm had a prevailing straight west wind in high levels, an anticyclone in lower levels, and a surface cold front moving fast.The specific humidity that less than 6 g·kg-1, and the relative humidity that less than 30% below 850 hPa indicated that the atmosphere was very dry. It had convective instability caused by temperature advection. (2) There was much strong vertical wind shear in the whole vertical layer for 814 storm case, the clockwise wind direction with height within 500-1500 m intensified the warm and humidity inflow of lower layer advantageous to storm initiation and development. While there was weak vertical wind shear and unobvious warm and humidity inflow of lower layer for 824 case, which was not conducive to storm initiation and development. In addition, composited wind of the whole troposphere and storm movement speed were very low for 814 case, but they were very high for 824 case. (3) The 814 storm was formed by the collision and mergence of multi cell storms, a convergence line was formed by the cold pool outflow produced by the precipitation of the upstream of thunderstorm cell and the east wind in low levels which forced the low level warm and moist air to uplift, additionally the strong convective instability and vertical wind shear supported the formation and development of new storm. The interactions (collisions) of gust fronts in the leading edge of cold pool of multi cell thunderstorm group, further exacerbating the low level instability, leading to the regeneration and mergence of new convective thunderstorms. The 824 storm was a line convective system accompanied with cold front that rapid moved eastward and lasted for short time, there was no east wind with warm and moisture air accompanying the cold pool outflow produced by the downdrafts of thunderstorm. The absence of mesoscale lifting mechanism and moisture inflow couldn’t support the formation and development of new storm.
Using the Variational Doppler Radar Analysis System (VDRAS) combined with local unconventional observation data, a more in depth contrastive analysis is carried on the initiation mechanism of two storm cases in Beijing, one is 814 (August 14, 2008) case with strong rainfall that we call it as moist storm and the other is 824 (August 24, 2008) case with little rainfall that we call it as dry storm. The results show: (1) The synoptic scale systems of 814 storm were stable Northeast cold vortex low trough at 500 hPa and shear line at 850 hPa, the specific humidity that more than 12 g·kg-1 below 850 hPa and the relative humidity that more than 90% in the surface indicated that the atmosphere was very moist. It had convective instability caused by humidity advection in lower levels. The 824 storm had a prevailing straight west wind in high levels, an anticyclone in lower levels, and a surface cold front moving fast.The specific humidity that less than 6 g·kg-1, and the relative humidity that less than 30% below 850 hPa indicated that the atmosphere was very dry. It had convective instability caused by temperature advection. (2) There was much strong vertical wind shear in the whole vertical layer for 814 storm case, the clockwise wind direction with height within 500-1500 m intensified the warm and humidity inflow of lower layer advantageous to storm initiation and development. While there was weak vertical wind shear and unobvious warm and humidity inflow of lower layer for 824 case, which was not conducive to storm initiation and development. In addition, composited wind of the whole troposphere and storm movement speed were very low for 814 case, but they were very high for 824 case. (3) The 814 storm was formed by the collision and mergence of multi cell storms, a convergence line was formed by the cold pool outflow produced by the precipitation of the upstream of thunderstorm cell and the east wind in low levels which forced the low level warm and moist air to uplift, additionally the strong convective instability and vertical wind shear supported the formation and development of new storm. The interactions (collisions) of gust fronts in the leading edge of cold pool of multi cell thunderstorm group, further exacerbating the low level instability, leading to the regeneration and mergence of new convective thunderstorms. The 824 storm was a line convective system accompanied with cold front that rapid moved eastward and lasted for short time, there was no east wind with warm and moisture air accompanying the cold pool outflow produced by the downdrafts of thunderstorm. The absence of mesoscale lifting mechanism and moisture inflow couldn’t support the formation and development of new storm.
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