ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 45,Issue 2,2019 Table of Contents
2019, 45(2):141-154.
DOI: 10.7519/j.issn.1000-0526.2019.02.001
Abstract:
A largescale severe convection weather event occurred in South China and Jiangnan Region during 4-5 March 2018. Many places were hit by thunderstorm, hail and shorttime intense precipitation, and, especially in Jiangxi Province, severe gale disaster was caused by squall line. Based on the characteristics of atmospheric circulation and radar echo evolution, the process can be divided into three stages: initial stage, developing stage and weakening stage. In the initial stage, the low pressure trough caused by southwest jet before westerly trough provided largescale trigger conditions for the severe convection; in the developing stage, squall line occurred before the trough of warm zone, characterized by extremely strong winds; after into the night, the cold front invaded from the north, making the low pressure trough and severe convection weakening. The diagnosis of ambient field and convective parameters shows that the high lowlevel temperature and humidity, dry and cold middlelevel air, and large temperature lapse rate are conducive to the generation of thunderstorm and extreme gale. The analysis of longtime series of soundings at Nanchang Station shows that the climate states of temperature and humidity are abnormal. Compared with the same period in history, the bottom layer was obviously warmer and wetter, and the middle layer was drier, which is beneficial to the occurrence of extreme convection. Analyzing the multisource observation data and radar data, we summarize the characteristics and causes of the Jiangxi squall line event during this process as follows. (1) Under the combined action of steering flow and forward propagation, the squall line moved very fast. (2) Surface pressure field presented strong thunderstorm high after squall front and the leading low caused strong density flow, which is conducive to extensive straightline gale at the mature stage of squall line. (3) The comparisons of the northsouth structural difference of the squallline bow echoes show that precipitation particles fallen in the midlevel dry rear inflow and the sharp cooling formed the strong sinking motion (downburst), which is a major cause for the extreme winds. The enhancement of thunderstorm high pressure caused by the downdraft in the stratus clouds and the downward momentum transportation both enhanced the thunderstorm gale.
A largescale severe convection weather event occurred in South China and Jiangnan Region during 4-5 March 2018. Many places were hit by thunderstorm, hail and shorttime intense precipitation, and, especially in Jiangxi Province, severe gale disaster was caused by squall line. Based on the characteristics of atmospheric circulation and radar echo evolution, the process can be divided into three stages: initial stage, developing stage and weakening stage. In the initial stage, the low pressure trough caused by southwest jet before westerly trough provided largescale trigger conditions for the severe convection; in the developing stage, squall line occurred before the trough of warm zone, characterized by extremely strong winds; after into the night, the cold front invaded from the north, making the low pressure trough and severe convection weakening. The diagnosis of ambient field and convective parameters shows that the high lowlevel temperature and humidity, dry and cold middlelevel air, and large temperature lapse rate are conducive to the generation of thunderstorm and extreme gale. The analysis of longtime series of soundings at Nanchang Station shows that the climate states of temperature and humidity are abnormal. Compared with the same period in history, the bottom layer was obviously warmer and wetter, and the middle layer was drier, which is beneficial to the occurrence of extreme convection. Analyzing the multisource observation data and radar data, we summarize the characteristics and causes of the Jiangxi squall line event during this process as follows. (1) Under the combined action of steering flow and forward propagation, the squall line moved very fast. (2) Surface pressure field presented strong thunderstorm high after squall front and the leading low caused strong density flow, which is conducive to extensive straightline gale at the mature stage of squall line. (3) The comparisons of the northsouth structural difference of the squallline bow echoes show that precipitation particles fallen in the midlevel dry rear inflow and the sharp cooling formed the strong sinking motion (downburst), which is a major cause for the extreme winds. The enhancement of thunderstorm high pressure caused by the downdraft in the stratus clouds and the downward momentum transportation both enhanced the thunderstorm gale.
2019, 45(2):155-165.
DOI: 10.7519/j.issn.1000-0526.2019.02.002
Abstract:
Based on the Doppler radar data, surface observation and rawinsonde data collected from April to September during 2000-2017, 35 squall line cases in the YangtzeHuaihe Area are identified. These squall lines occur most frequently in the plain to the north of the Yangtse River. The squall lines peak in July and a large proportion of them generate in early afternoon, mature in late afternoon, and dissipate in evening. The squall lines have a dominant southeast motion at the speed of 8-16 m·s-1. They are characterized by the maximum length of 200-250 km, the maximum intensity of 60-65 dBz, and the duration of 3-4 h. The squall lines commonly form in a brokenareal pattern, display a trailingstratiform pattern, and dissipate in a reversed brokenline pattern. The ambient flows of the squall lines are classified into five synoptic patterns, which are preshort trough, prelong trough, cold vortex, around subtropicalhigh and posttrough patterns. About 62.9% of the squall lines form in the dominant pretrough pattern. Prelong trough squall line causes the largest surface cooling. The radar echo cores of prelong trough and cold vortex squall lines are higher and the weather is more severe. Besides precipitation and thunderstorms, hail or tornado can also occur. Favorable conditions for the different patterns have been analyzed in the terms of instability, vertical wind shear and so on.
Based on the Doppler radar data, surface observation and rawinsonde data collected from April to September during 2000-2017, 35 squall line cases in the YangtzeHuaihe Area are identified. These squall lines occur most frequently in the plain to the north of the Yangtse River. The squall lines peak in July and a large proportion of them generate in early afternoon, mature in late afternoon, and dissipate in evening. The squall lines have a dominant southeast motion at the speed of 8-16 m·s-1. They are characterized by the maximum length of 200-250 km, the maximum intensity of 60-65 dBz, and the duration of 3-4 h. The squall lines commonly form in a brokenareal pattern, display a trailingstratiform pattern, and dissipate in a reversed brokenline pattern. The ambient flows of the squall lines are classified into five synoptic patterns, which are preshort trough, prelong trough, cold vortex, around subtropicalhigh and posttrough patterns. About 62.9% of the squall lines form in the dominant pretrough pattern. Prelong trough squall line causes the largest surface cooling. The radar echo cores of prelong trough and cold vortex squall lines are higher and the weather is more severe. Besides precipitation and thunderstorms, hail or tornado can also occur. Favorable conditions for the different patterns have been analyzed in the terms of instability, vertical wind shear and so on.
2019, 45(2):166-179.
DOI: 10.7519/j.issn.1000-0526.2019.02.003
Abstract:
A Jianghuai cyclone which caused regional severe torrential rain in East China and extreme precipitation events at several stations in Jiangsu Province during 9-10 June 2017 is analyzed based on NCEP 0.25°×0.25° reanalysis data and multiple observation data. The generation, development, front structure and equivalent barotropy are studied by comparing with another Jianghuai cyclone with less precipitation. The results are as follows. (1) The divergence caused by positive vorticity advection and distributary at upper troposphere led to the generation of the “0609” (9 June 2017) cyclone while the warm advection at lower troposphere triggered the “0605” (5 June 2017) cyclone. (2) The calculation of frontogenesis function indicates that frontogenesis was much intenser in the “0609” cyclone than the other which made the frontal surface less tilted and the upward motion in warm area much stronger and deeper. These factors and the slow motion of front could be the direct reason for the regional torrential rain. (3) Vertical profile of relative vorticity and 0 contour of zonal wind indicates that the “0609” cyclone had an intense vorticity column and vertical structure below 700 hPa, which made itself some equivalent barotropic, while the “0605” cyclone had a tilted structure and it was more baroclinic. (4) The latent heat released by intense precipitation could strengthen the cyclone by mixing vorticity and the strengthened cyclone could enhance the precipitation conversely, creating a positive feedback mechanism like CISK between cyclone and its precipitation. This could be the reason for the equivalent barotropy of the “0609” cyclone, showing the multiple evolution pattern of Jianghuai cyclone.
A Jianghuai cyclone which caused regional severe torrential rain in East China and extreme precipitation events at several stations in Jiangsu Province during 9-10 June 2017 is analyzed based on NCEP 0.25°×0.25° reanalysis data and multiple observation data. The generation, development, front structure and equivalent barotropy are studied by comparing with another Jianghuai cyclone with less precipitation. The results are as follows. (1) The divergence caused by positive vorticity advection and distributary at upper troposphere led to the generation of the “0609” (9 June 2017) cyclone while the warm advection at lower troposphere triggered the “0605” (5 June 2017) cyclone. (2) The calculation of frontogenesis function indicates that frontogenesis was much intenser in the “0609” cyclone than the other which made the frontal surface less tilted and the upward motion in warm area much stronger and deeper. These factors and the slow motion of front could be the direct reason for the regional torrential rain. (3) Vertical profile of relative vorticity and 0 contour of zonal wind indicates that the “0609” cyclone had an intense vorticity column and vertical structure below 700 hPa, which made itself some equivalent barotropic, while the “0605” cyclone had a tilted structure and it was more baroclinic. (4) The latent heat released by intense precipitation could strengthen the cyclone by mixing vorticity and the strengthened cyclone could enhance the precipitation conversely, creating a positive feedback mechanism like CISK between cyclone and its precipitation. This could be the reason for the equivalent barotropy of the “0609” cyclone, showing the multiple evolution pattern of Jianghuai cyclone.
2019, 45(2):180-190.
DOI: 10.7519/j.issn.1000-0526.2019.02.004
Abstract:
Based on SWAN (Severe Weather Automatic Nowcast System) radar mosaic products, we selected the composite reflectivity factor and its horizontal gradient, echo top height and vertically integrated liquid water content as identification parameters, and conducted a classification test for convective cloud and stratiform cloud precipitation in rainstorm processes using the fuzzy logic method. The results were verified by 12 regional rainstorm processes that occurred in Chongqing. Taking the Advanced TOA and Direction System lightning data as objective observation data of convective cloud precipitation, we tested the related products quantitatively by four different radiuses of spatial matching and four different time matching methods, respectively. The verification results showed that with the increase of space matching radius, the correct rate improves significantly. However, the correct rate of 6 min cloudtoground lightning flashes relative to 6 min mosaic products ahead of 6 min, 3 min, 0 min and lagging 3 min four time matching methods, changes slightly. The overall score of the rainstorm is high and the test method has clear physical meaning. The score results under different temporal and spatial matching patterns are consistent with the actual situation, which means the classification outcome of the convective and stratiform rainfall is good. This is an exploration of convective cloud precipitation quantitative test as well.
Based on SWAN (Severe Weather Automatic Nowcast System) radar mosaic products, we selected the composite reflectivity factor and its horizontal gradient, echo top height and vertically integrated liquid water content as identification parameters, and conducted a classification test for convective cloud and stratiform cloud precipitation in rainstorm processes using the fuzzy logic method. The results were verified by 12 regional rainstorm processes that occurred in Chongqing. Taking the Advanced TOA and Direction System lightning data as objective observation data of convective cloud precipitation, we tested the related products quantitatively by four different radiuses of spatial matching and four different time matching methods, respectively. The verification results showed that with the increase of space matching radius, the correct rate improves significantly. However, the correct rate of 6 min cloudtoground lightning flashes relative to 6 min mosaic products ahead of 6 min, 3 min, 0 min and lagging 3 min four time matching methods, changes slightly. The overall score of the rainstorm is high and the test method has clear physical meaning. The score results under different temporal and spatial matching patterns are consistent with the actual situation, which means the classification outcome of the convective and stratiform rainfall is good. This is an exploration of convective cloud precipitation quantitative test as well.
2019, 45(2):191-202.
DOI: 10.7519/j.issn.1000-0526.2019.02.005
Abstract:
Based on automatic weather station, dense and routine observation data, this study analyzes the characteristics of snow cover and its meteorological impact factors on a case of Jianghuai cyclone snowstorm that occurred from 21 to 22 February 2017. The results show that the typical spatial structure of Jianghuai cyclone led to the different snowfall amounts and depths in Shandong. The snow cover peaked when the snow ended and its persistence depended on temperature, so snow depth was of timeliness. Commonly, snow depth is affected by multiple meteorological factors of surface, including precipitation type, snowfall amount, snowfall intensity, temperature, soil temperature and wind speed. Sleet can produce snow cover below 1 cm if it turns to pure snow. Average snowtoliquid ratio in Shandong is 0.5 cm·mm-1, lower than the value for the whole country. Large snowfall, strong snowfall intensity, low air and soil temperatures are beneficial to snow depth. Enough snow intensity is necessary for obvious snow cover when air and soil temperatures are both higher than 0℃. It’s common that soil temperature drops quickly before visible snow cover and rises stably within 1 to 2 hours. Air temperature is usually below 0℃ when snow cover forms. Weak wind speed under Grade 2 is good for snow cover to form.
Based on automatic weather station, dense and routine observation data, this study analyzes the characteristics of snow cover and its meteorological impact factors on a case of Jianghuai cyclone snowstorm that occurred from 21 to 22 February 2017. The results show that the typical spatial structure of Jianghuai cyclone led to the different snowfall amounts and depths in Shandong. The snow cover peaked when the snow ended and its persistence depended on temperature, so snow depth was of timeliness. Commonly, snow depth is affected by multiple meteorological factors of surface, including precipitation type, snowfall amount, snowfall intensity, temperature, soil temperature and wind speed. Sleet can produce snow cover below 1 cm if it turns to pure snow. Average snowtoliquid ratio in Shandong is 0.5 cm·mm-1, lower than the value for the whole country. Large snowfall, strong snowfall intensity, low air and soil temperatures are beneficial to snow depth. Enough snow intensity is necessary for obvious snow cover when air and soil temperatures are both higher than 0℃. It’s common that soil temperature drops quickly before visible snow cover and rises stably within 1 to 2 hours. Air temperature is usually below 0℃ when snow cover forms. Weak wind speed under Grade 2 is good for snow cover to form.
2019, 45(2):203-215.
DOI: 10.7519/j.issn.1000-0526.2019.02.006
Abstract:
Based on conventional automatic meteorological data, FY2G satellite data, Doppler radar data and other related data, a localized severe storm under the influence of subtropical high in Chongqing is analyzed and simulated. This paper discusses evolution process of mesoscale convective system (MCS), triggering and maintaining mechanism. The results show that mesoscale environment of high temperature, high humidity air mass and extreme unstable atmospheric stratification conditions were provided under the influence of subtropical high. The triggering key factor of the local convective storm was mesoscale convergence line in shallow boundary near the ground. The convergence line was generated by combined contribution from thunderstorm high pressure of MCS in the central and western Sichuan and Chongqing Basin and the surface thermal low in Chongqing. Small range of cold pool outflow was generated by convective storm triggered by convergence line. A new convergence line was formed by small range of pool generated by convective storm triggered by mesoscale convergence line and ground ambient wind, strengthening development of convection storm and triggering new convection cells. The convective cells moved slowly northward under the average south wind in the bearing layer. Thus the cold pool outflow and the boundary convergence lines caused convective cells to propagate northwestward and maintain a long time.
Based on conventional automatic meteorological data, FY2G satellite data, Doppler radar data and other related data, a localized severe storm under the influence of subtropical high in Chongqing is analyzed and simulated. This paper discusses evolution process of mesoscale convective system (MCS), triggering and maintaining mechanism. The results show that mesoscale environment of high temperature, high humidity air mass and extreme unstable atmospheric stratification conditions were provided under the influence of subtropical high. The triggering key factor of the local convective storm was mesoscale convergence line in shallow boundary near the ground. The convergence line was generated by combined contribution from thunderstorm high pressure of MCS in the central and western Sichuan and Chongqing Basin and the surface thermal low in Chongqing. Small range of cold pool outflow was generated by convective storm triggered by convergence line. A new convergence line was formed by small range of pool generated by convective storm triggered by mesoscale convergence line and ground ambient wind, strengthening development of convection storm and triggering new convection cells. The convective cells moved slowly northward under the average south wind in the bearing layer. Thus the cold pool outflow and the boundary convergence lines caused convective cells to propagate northwestward and maintain a long time.
2019, 45(2):216-227.
DOI: 10.7519/j.issn.1000-0526.2019.02.007
Abstract:
Based on the high-resolution data provided by FY-2F geostationary meteorological satellite from May to September in 2015, the cloud-top physical characteristics, including the height of cloud top, cloud top cooling rate (CTC), multi-channels differences, etc, were analyzed and compared from the stage of convective initiation (CI) to the development phase in deep and shallow convections which were identified by the temperature threshold method. The results indicate that the cloud-top physical characteristics in the stage of CI in deep and shallow convections have the similar trend that the height of cloud top ascends rapidly in a short time and CTC values decrease first and increase subsequently. The differences between deep and shallow convections are as follows. The ascending height of deep convection cloud top can exceed that of vapor layer, and vice versa. The CTC values of deep convection show even lower compared with that of shallow convection. Based on the differences of minimum CTC in the stage of CI in deep and shallow convections, the verified case demonstrates that using the differences of minimum CTC is capable of judging whether CI could develop into deep convection on the basis of identified CI, and then early war-ning could be worked out.
Based on the high-resolution data provided by FY-2F geostationary meteorological satellite from May to September in 2015, the cloud-top physical characteristics, including the height of cloud top, cloud top cooling rate (CTC), multi-channels differences, etc, were analyzed and compared from the stage of convective initiation (CI) to the development phase in deep and shallow convections which were identified by the temperature threshold method. The results indicate that the cloud-top physical characteristics in the stage of CI in deep and shallow convections have the similar trend that the height of cloud top ascends rapidly in a short time and CTC values decrease first and increase subsequently. The differences between deep and shallow convections are as follows. The ascending height of deep convection cloud top can exceed that of vapor layer, and vice versa. The CTC values of deep convection show even lower compared with that of shallow convection. Based on the differences of minimum CTC in the stage of CI in deep and shallow convections, the verified case demonstrates that using the differences of minimum CTC is capable of judging whether CI could develop into deep convection on the basis of identified CI, and then early war-ning could be worked out.
2019, 45(2):228-239.
DOI: 10.7519/j.issn.1000-0526.2019.02.008
Abstract:
Based on Fujian dense automatic station data, wind profile radar data, Sband dual polarization radar data, raindrop spectrum data and NCEP 1°×1° reanalysis data, the failed forecast of winter torrential rain for central and southern Fujian from 20:00 BT 21 to 20:00 BT 22 February 2017 is analyzed. The results suggest that: (1) The uncommon torrential rain happened ahead of the front, under the background of strong and long persisting lowlevel jet, seen only once since 2000, and was not affected by the southern trough and cold air. (2) Convective systems in central and southern Fujian were independent to each other, and multiple convective systems affected central Fujian, but only two affected southern Fujian. The convective precipitation was warm rain process convection, easily causing the underestimation of rainfall intensity. (3) The water vapor came mainly from the South China Sea. Compared with heavy rain events in flood season, the lowlevel water vapor condition was similar to that of flood season although water vapor in the whole layer was slightly weaker. Warm and wet air transport by lowlevel jet increased the instability of stratification in rainstorm area, but the convective instability was slightly weaker than that in the flood season. (4) Divergence at upper layer coupling with lowlayer convergence provided favorable condition for the dynamic lifting of rainstorm areas, but the wind vorticity was not strong and there was no obvious positive vorticity column. Analysis of wet potential vorticity indicates that the heavytotrorrential rain in central Fujian was mainly related to conditional symmetric instability, resulting in the inclining ascending motion, but both convective instability and conditional symmetric instability played great roles in the rainstorm area in southern Fujian.
Based on Fujian dense automatic station data, wind profile radar data, Sband dual polarization radar data, raindrop spectrum data and NCEP 1°×1° reanalysis data, the failed forecast of winter torrential rain for central and southern Fujian from 20:00 BT 21 to 20:00 BT 22 February 2017 is analyzed. The results suggest that: (1) The uncommon torrential rain happened ahead of the front, under the background of strong and long persisting lowlevel jet, seen only once since 2000, and was not affected by the southern trough and cold air. (2) Convective systems in central and southern Fujian were independent to each other, and multiple convective systems affected central Fujian, but only two affected southern Fujian. The convective precipitation was warm rain process convection, easily causing the underestimation of rainfall intensity. (3) The water vapor came mainly from the South China Sea. Compared with heavy rain events in flood season, the lowlevel water vapor condition was similar to that of flood season although water vapor in the whole layer was slightly weaker. Warm and wet air transport by lowlevel jet increased the instability of stratification in rainstorm area, but the convective instability was slightly weaker than that in the flood season. (4) Divergence at upper layer coupling with lowlayer convergence provided favorable condition for the dynamic lifting of rainstorm areas, but the wind vorticity was not strong and there was no obvious positive vorticity column. Analysis of wet potential vorticity indicates that the heavytotrorrential rain in central Fujian was mainly related to conditional symmetric instability, resulting in the inclining ascending motion, but both convective instability and conditional symmetric instability played great roles in the rainstorm area in southern Fujian.
2019, 45(2):240-250.
DOI: 10.7519/j.issn.1000-0526.2019.02.009
Abstract:
Based on the obversation data and detailed metadata archive recorded by 129 meteorological stations in the northeast of China, the homogeneity test and corrections are carried out to the monthly maximum and minimum temperatures by using the penalized maximum T test (PMT), and the corrections have been compared to the previous study (CHHT). The results show that the discontinuities of monthly temperature are prevalent which are mainly caused by data joint from different resoures and station relocation. There are 74 and 94 breakpoints detected respectively from monthly maximum and minimum temperatures. The spatial consistency of the monthly maximum and minimum temperatures has been improved and the spatial distribution of longterm trends is more reasonable after data homogenization. The trends of annual maximum and minimum temperatures have respectively increased from 0.1℃·(10 a)-1 and 0.22℃·(10 a)-1 to 0.17℃·(10 a)-1 and 0.33℃·(10 a)-1. Compared to the CHHT, temporal correlation coefficient between PMT and CHHT is above 0.9, reflecting the consistent climate warming. The spatial distribution of longterm trends is slightly improved and the trends of annual maximum and minimum temperature calculated by PMT are 0.05℃·(10 a)-1 and 0.03℃·(10 a)-1 warmer than those by CHHT.
Based on the obversation data and detailed metadata archive recorded by 129 meteorological stations in the northeast of China, the homogeneity test and corrections are carried out to the monthly maximum and minimum temperatures by using the penalized maximum T test (PMT), and the corrections have been compared to the previous study (CHHT). The results show that the discontinuities of monthly temperature are prevalent which are mainly caused by data joint from different resoures and station relocation. There are 74 and 94 breakpoints detected respectively from monthly maximum and minimum temperatures. The spatial consistency of the monthly maximum and minimum temperatures has been improved and the spatial distribution of longterm trends is more reasonable after data homogenization. The trends of annual maximum and minimum temperatures have respectively increased from 0.1℃·(10 a)-1 and 0.22℃·(10 a)-1 to 0.17℃·(10 a)-1 and 0.33℃·(10 a)-1. Compared to the CHHT, temporal correlation coefficient between PMT and CHHT is above 0.9, reflecting the consistent climate warming. The spatial distribution of longterm trends is slightly improved and the trends of annual maximum and minimum temperature calculated by PMT are 0.05℃·(10 a)-1 and 0.03℃·(10 a)-1 warmer than those by CHHT.
2019, 45(2):251-262.
DOI: 10.7519/j.issn.1000-0526.2019.02.010
Abstract:
Using the wind data observed from the 80 m meteorological tower in Dongguan of Guangdong Province during the passes of Typhoon Molave, severe convection and severe cold air, the mean wind and fluctuating wind characteristics of different strong wind weather systems in the nearsurface boundary layer are analyzed. The results show that: (1) the wind speed variation of the severe convection No.1 is most dramatic and the 10 min mean wind speed amplitude of severe convection can go up to 1.8 times and 3.7 times as much as that of typhoon and severe cold air. The 10 min mean wind direction amplitude can be 120°·(10 min)-1. (2) The power law exponent of typhoon strong wind profile is 0.177 which is larger than 0.15 that is recommended as the power law exponent of exposure class B in Chinese National Code (GB 5009-2012). The power law exponent of severe convection is near 0.12 which is recommended as the exposure class A in the code and the power law exponent of severe cold air is only 0.10. (3) The 10 min average turbulence intensity of No.1 severe convection can go up to 1.4-2.1 times and 1.7-2.0 times as much as that of typhoon and severe cold air. (4) The attack angles of typhoon and severe convection change between -3°-3° while the attack angle of severe cold air changes near 0°. (5) The turbulence integral length scales increase due to the impact of strong wind processes. The horizontal (longitudinal and transverse) turbulence integral length scales of typhoon can obviously increase by an order of magnitude. (6) The typhoon strong wind spectra does not satisfy the -5/3 law and the isotropy assumption. The power spectral density (PSD) value of typhoon is significantly larger than that of severe convection and severe cold air. The PSD value of typhoon is about 3 times as large as that of severe convection and severe cold air.
Using the wind data observed from the 80 m meteorological tower in Dongguan of Guangdong Province during the passes of Typhoon Molave, severe convection and severe cold air, the mean wind and fluctuating wind characteristics of different strong wind weather systems in the nearsurface boundary layer are analyzed. The results show that: (1) the wind speed variation of the severe convection No.1 is most dramatic and the 10 min mean wind speed amplitude of severe convection can go up to 1.8 times and 3.7 times as much as that of typhoon and severe cold air. The 10 min mean wind direction amplitude can be 120°·(10 min)-1. (2) The power law exponent of typhoon strong wind profile is 0.177 which is larger than 0.15 that is recommended as the power law exponent of exposure class B in Chinese National Code (GB 5009-2012). The power law exponent of severe convection is near 0.12 which is recommended as the exposure class A in the code and the power law exponent of severe cold air is only 0.10. (3) The 10 min average turbulence intensity of No.1 severe convection can go up to 1.4-2.1 times and 1.7-2.0 times as much as that of typhoon and severe cold air. (4) The attack angles of typhoon and severe convection change between -3°-3° while the attack angle of severe cold air changes near 0°. (5) The turbulence integral length scales increase due to the impact of strong wind processes. The horizontal (longitudinal and transverse) turbulence integral length scales of typhoon can obviously increase by an order of magnitude. (6) The typhoon strong wind spectra does not satisfy the -5/3 law and the isotropy assumption. The power spectral density (PSD) value of typhoon is significantly larger than that of severe convection and severe cold air. The PSD value of typhoon is about 3 times as large as that of severe convection and severe cold air.
2019, 45(2):263-273.
DOI: 10.7519/j.issn.1000-0526.2019.02.011
Abstract:
Based on the historical hourly wind observation data of eight coastal and inland automatic weather stations in Shenzhen from 1 June 2007 to 1 June 2017, this study explores the seasonal gust characteris tics and the feature of the gust factors for the eight stations. The results show that winds at coastal stations are generally stronger than the winds at inland stations. The maximum gust at the eight stations due to typhoons in summer and autumn is generally stronger than the maximum gust at these stations due to cold front in winter and spring. Among these stations, Yantian International Container Terminal Station (YTG), Mawan Port Station (MWG), Shekou Ferry Terminal Station (SKMT), which are located close to seawater, have relatively smaller gust factor, compared to the factors at other stations. With the increase of the distance to the coastline, the gust factor at the stations becomes bigger. Therefore, the gale tends to be more instantaneous at the stations with farther distance to coastline than the gale at coastal stations. Among the eight stations, Beizaijiao Station (BZJ) and YTG have the most frequent gust gale records. The historical maximum gusts at the two stations are above 12level scale (Beaufort scale), and the historical maximum 10 min average wind is above 9level scale at BZJ and 10level scale at YTG. Further case studies show that the gust gale in Shenzhen Area induced by severe convective weather is more instantaneous than those induced by typhoon or cold front. The location of the gust gale induced by severe convective weather is more stochastic. This study could provide references for the seasonal wind forecast and risk assessment in Shenzhen Area.
Based on the historical hourly wind observation data of eight coastal and inland automatic weather stations in Shenzhen from 1 June 2007 to 1 June 2017, this study explores the seasonal gust characteris tics and the feature of the gust factors for the eight stations. The results show that winds at coastal stations are generally stronger than the winds at inland stations. The maximum gust at the eight stations due to typhoons in summer and autumn is generally stronger than the maximum gust at these stations due to cold front in winter and spring. Among these stations, Yantian International Container Terminal Station (YTG), Mawan Port Station (MWG), Shekou Ferry Terminal Station (SKMT), which are located close to seawater, have relatively smaller gust factor, compared to the factors at other stations. With the increase of the distance to the coastline, the gust factor at the stations becomes bigger. Therefore, the gale tends to be more instantaneous at the stations with farther distance to coastline than the gale at coastal stations. Among the eight stations, Beizaijiao Station (BZJ) and YTG have the most frequent gust gale records. The historical maximum gusts at the two stations are above 12level scale (Beaufort scale), and the historical maximum 10 min average wind is above 9level scale at BZJ and 10level scale at YTG. Further case studies show that the gust gale in Shenzhen Area induced by severe convective weather is more instantaneous than those induced by typhoon or cold front. The location of the gust gale induced by severe convective weather is more stochastic. This study could provide references for the seasonal wind forecast and risk assessment in Shenzhen Area.
2019, 45(2):274-281.
DOI: 10.7519/j.issn.1000-0526.2019.02.012
Abstract:
Based on surface meteorological observations and yield data of winter wheat at 103 stations in Henan Province from 1971 to 2014, the characteristics of winter wheat drought damage were analyzed. Besides, the drought condition at jointing-heading stage, which has a serious effect on yield was selected as a meteorological disaster type of the model design of the weather index insurance and the disaster risk assessment was carried out. Negative anomaly percentage of precipitation was defined as drought index of winter wheat and the model that described the relationship between drought index and yield reduction was also established using 173 groups of typical disaster samples. On this basis, the weather index insurance product of winter wheat drought damage was developed and the premium rates of different regions were revised based on the results of the drought risk assessment. The results showed that the level of winter wheat drought increases from the southwestern part to the northeastern part in Henan Province. During the jointing-heading stage, the highest risk was found in the northern part, followed by the northwestern, eastern and central parts, and the risk of the southwestern and the southern parts is relatively lower. Based on the drought index model and the analysis of historical payments, negative anomaly percentage of precipitation of 60% was considered as the payment trigger value, and the payment standards of different levels of drought weather index were determined. Considering the results of the drought risk assessment, the revised premium rates of different regions in Henan are 9.2%-11.2%, and corresponding premiums of unit area are 29.8-36.3 Yuan·mu-1.
Based on surface meteorological observations and yield data of winter wheat at 103 stations in Henan Province from 1971 to 2014, the characteristics of winter wheat drought damage were analyzed. Besides, the drought condition at jointing-heading stage, which has a serious effect on yield was selected as a meteorological disaster type of the model design of the weather index insurance and the disaster risk assessment was carried out. Negative anomaly percentage of precipitation was defined as drought index of winter wheat and the model that described the relationship between drought index and yield reduction was also established using 173 groups of typical disaster samples. On this basis, the weather index insurance product of winter wheat drought damage was developed and the premium rates of different regions were revised based on the results of the drought risk assessment. The results showed that the level of winter wheat drought increases from the southwestern part to the northeastern part in Henan Province. During the jointing-heading stage, the highest risk was found in the northern part, followed by the northwestern, eastern and central parts, and the risk of the southwestern and the southern parts is relatively lower. Based on the drought index model and the analysis of historical payments, negative anomaly percentage of precipitation of 60% was considered as the payment trigger value, and the payment standards of different levels of drought weather index were determined. Considering the results of the drought risk assessment, the revised premium rates of different regions in Henan are 9.2%-11.2%, and corresponding premiums of unit area are 29.8-36.3 Yuan·mu-1.
2019, 45(2):282-289.
DOI: 10.7519/j.issn.1000-0526.2019.02.013
Abstract:
Based on the daily observation data of acid rain in Wuhan during 1990-2014, we studied the variation of acid rain and its relationship with rainfall intensity, wind, air mass source and pollutant source. The results indicated that the precipitation in Wuhan shows weak acidity and the annual mean pH is 4.86. The acid rain intensity showed an increasing trend in general but has tended to weaken since 2007. The annual mean electrical conductivity is 50.3 μS·cm-1 with a rise of 8.8 μS·cm-1 per decade. The pH value is lower in winter than in summer while the frequency and electrical conductivity are higher in winter than in summer. The conductivity and pH value of intense acid rain have an obvious negative correlation while a significant positive correlation is for nonacid rain. The rainfall intensity is an important factor in the development of acid rain intensity and frequency, showing differences in different seasons. The intensity and the frequency of acid rain decrease when the wind speed at 1500 m height increases. Acid rain occurs more in southwest wind direction. The intense acid rain is mainly affected by acid rain from the south heavy air pollution area, and the external pollution sources by the atmospheric transmission contribute greatly to the intense acid rain in Wuhan. The sulphur dioxide content (SO2) in Wuhan tends to decline while the nitrogen dioxide content (NO2) tends to increase. The total concentrations of the two have presented a decreasing trend since 2000.
Based on the daily observation data of acid rain in Wuhan during 1990-2014, we studied the variation of acid rain and its relationship with rainfall intensity, wind, air mass source and pollutant source. The results indicated that the precipitation in Wuhan shows weak acidity and the annual mean pH is 4.86. The acid rain intensity showed an increasing trend in general but has tended to weaken since 2007. The annual mean electrical conductivity is 50.3 μS·cm-1 with a rise of 8.8 μS·cm-1 per decade. The pH value is lower in winter than in summer while the frequency and electrical conductivity are higher in winter than in summer. The conductivity and pH value of intense acid rain have an obvious negative correlation while a significant positive correlation is for nonacid rain. The rainfall intensity is an important factor in the development of acid rain intensity and frequency, showing differences in different seasons. The intensity and the frequency of acid rain decrease when the wind speed at 1500 m height increases. Acid rain occurs more in southwest wind direction. The intense acid rain is mainly affected by acid rain from the south heavy air pollution area, and the external pollution sources by the atmospheric transmission contribute greatly to the intense acid rain in Wuhan. The sulphur dioxide content (SO2) in Wuhan tends to decline while the nitrogen dioxide content (NO2) tends to increase. The total concentrations of the two have presented a decreasing trend since 2000.
2019, 45(2):290-296.
DOI: 10.7519/j.issn.1000-0526.2019.02.014
Abstract:
The main characteristics of the general atmospheric circulation in November 2018 are as follow. There was one polar vortex center in the Northern Hemisphere. The circulation presented a fourwave pattern in middlehigh latitudes. The East Asian trough behaved weakly. There were two major rainfall processes in this month and the monthly mean precipitation over China was 24.9 mm, which is 32.4% more than normal. Monthly mean temperature was 3.1℃, which is 0.2℃ higher than normal. There were four cold air processes in this month, two of which were moderateintensity cold air processes nationwide. Additionally, there were two foghaze processes in this month. From November 24 to December 3, the haze process mixed with dust aerosols occurred in northern China, which was the most widely, the longest and the heaviest one since autumn of 2018.
The main characteristics of the general atmospheric circulation in November 2018 are as follow. There was one polar vortex center in the Northern Hemisphere. The circulation presented a fourwave pattern in middlehigh latitudes. The East Asian trough behaved weakly. There were two major rainfall processes in this month and the monthly mean precipitation over China was 24.9 mm, which is 32.4% more than normal. Monthly mean temperature was 3.1℃, which is 0.2℃ higher than normal. There were four cold air processes in this month, two of which were moderateintensity cold air processes nationwide. Additionally, there were two foghaze processes in this month. From November 24 to December 3, the haze process mixed with dust aerosols occurred in northern China, which was the most widely, the longest and the heaviest one since autumn of 2018.
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ISSN:1000-0526 CN:11-2282/P