Based on the previous statistical analysis of mesoscale convective systems(MCSs)over the second-step terrain along Yangtze-Huaihe River Valley,eight representative long-lived eastward-propagating MCSs are selected for...Based on the previous statistical analysis of mesoscale convective systems(MCSs)over the second-step terrain along Yangtze-Huaihe River Valley,eight representative long-lived eastward-propagating MCSs are selected for model-based sensitivity testing to investigate the initiation and evolution of these types of MCSs as well as their impact on downstream areas.We subject each MCS to a semi-idealized(CNTL)simulation and a sensitivity(NOLH)simulation that neglects condensational heating in the formation region.The CNTL experiment reveals convection forms in the region downstream of a shortwave trough typified by persistent southwesterly winds in the low-to midtroposphere.Upon merging with other convective systems,moist convection develops into an MCS,which propagates eastward under the influence of mid-tropospheric westerlies,and moves out of the second-step terrain.The MCS then merges with pre-existing local convection over the plains;the merged convection reinforces the cyclonic wind perturbation into a mesoscale vortex at 850 hPa.While this vortex moves eastward to regions with local vortex at 850 hPa,another vortex at 925 hPa is also intensified.Finally,the vortices at 850 and 925 hPa merge together and develop into a mesoscale convective vortex(MCV).In contrast,MCSs fail to form and move eastward in the NOLH experiment.In the absence of eastward-propagating MCSs,moist convection and mesoscale vortices still appear in the plains,but the vortex strength and precipitation intensity are significantly weakened.It is suggested the eastward-propagating MCSs over the second-step terrain significantly impact the development and enhancement of moist convection and vortices in the downstream areas.展开更多
Based on the significant weather report,CG lightning,composite radar reflectivity,and ERA5 reanalysis data,we first studied the spatiotemporal distribution characteristics of four types(only severe convective wind(SCW...Based on the significant weather report,CG lightning,composite radar reflectivity,and ERA5 reanalysis data,we first studied the spatiotemporal distribution characteristics of four types(only severe convective wind(SCW);SCW and hail;SCW and short-duration heavy rainfall(SDHR);and SCW,hail,and SDHR)of convective weather events related to SCW during the warm season(May to September)from 2011 to 2018 in North China.Second,severe convective cases producing SCW were selected to statistically analyze the initiation,decay,lifetime,and organizational characteristics of convective systems.Finally,using ERA5 reanalysis data and conventional surface observation data,preconvective soundings were constructed to explore the differences in environmental conditions for initiating convective systems between SCW and non-SCW.The results indicate that mixed-type of SCW and SDHR events occur more frequently over plains,while other types of convective weather occur more frequently over mountains.The frequency peak of SCW occurs in June,while mixed convective weather peaks in July.The initiation time of convective systems is concentrated between 1000 and 1300 BST,with a peak at 1200 BST.Over mountains,the daily peaks of ordinary and significant SCW generally occur at 1700-1800 BST and 1600-1700 BST,respectively,while over plains,the peak of ordinary SCW typically lags behind that of mountains by 1-2 hours.Additionally,SCW systems are mainly initiated over mountains,with most lifetimes lasting 7–13 hours.Nonlinear convective systems produce the most SCW events,followed by trailing-stratiform convective systems.The convective available potential energy(CAPE),downdraft convective available potential energy,and the temperature difference between 850 and 500 hPa can all distinguish between SCW systems and non-SCW systems occurring over plains.Compared to non-SCW convective systems,SCW convective systems over mountains are more likely to occur in environments with less precipitable water,while SCW convective systems over plains are more likely to occur in environments with higher CAPE and stronger deep-layer wind shear.展开更多
Located in the Asian monsoon region, China frequently experiences severe convective weather(SCW), such as short-duration heavy rainfall(SDHR), thunderstorm high winds, hails, and occasional tornadoes. Progress in SCW ...Located in the Asian monsoon region, China frequently experiences severe convective weather(SCW), such as short-duration heavy rainfall(SDHR), thunderstorm high winds, hails, and occasional tornadoes. Progress in SCW forecasting in China is closely related to the construction and development of meteorological observation networks,especially weather radar and meteorological satellite networks. In the late 1950 s, some county-level meteorological bureaus began to conduct empirical hail forecasting based on observations of clouds and surface meteorological variables. It took over half a century to develop a modern comprehensive operational monitoring and warning system for SCW forecast nationwide since the setup of the first weather radar in 1959. The operational SCW forecasting, including real-time monitoring, warnings valid for tens of minutes, watches valid for several hours, and outlooks covering lead times of up to three days, was established in 2009. Operational monitoring and forecasting of thunderstorms,SDHR, thunderstorm high winds, and hails have been carried out. The performance of operational SCW forecasting will be continually improved in the future with the development of convection-resolving numerical models(CRNMs), the upgrade of weather radar networks, the launch of new-generation meteorological satellites, better understanding of meso-γ and microscale SCW systems, and further application of artificial intelligence technology and CRNM predictions.展开更多
This study investigates classification and diurnal variations of the precipitation echoes over the central Tibetan Plateau based on the observations collected from a C-band vertically-pointing frequency-modulated cont...This study investigates classification and diurnal variations of the precipitation echoes over the central Tibetan Plateau based on the observations collected from a C-band vertically-pointing frequency-modulated continuous-wave(C-FMCW)radar during the Third Tibetan Plateau Atmospheric Scientific Experiment(TIPEX-Ⅲ)2014-Intensive Observation Period(2014-IOP).The results show that 51.32%of the vertical profiles have valid echoes with reflectivity>–10 dBZ,and 35.06% of the valid echo profiles produce precipitation at the ground(precipitation profiles);stratiform precipitation with an evident bright-band signature,weak convective precipitation,and strong convective precipitation account for 52.03%,42.98%,and 4.99% of the precipitation profiles,respectively.About 59.84% of the precipitation occurs in the afternoon to midnight,while 40.16% of the precipitation with weaker intensity is observed in the nocturnal hours and in the morning.Diurnal variation of occurrence frequency of precipitation shows a major peak during 2100–2200 LST(local solar time)with 59.02%being the stratiform precipitation;the secondary peak appears during 1300–1400 LST with 59.71% being the weak convective precipitation;the strong convective precipitation occurs mostly(81.83%)in the afternoon and evening with two peaks over 1200–1300 and 1700–1800 LST,respectively.Starting from approximately 1100 LST,precipitation echoes develop with enhanced vertical air motion,elevated echo top,and increasing radar reflectivity.Intense upward air motion occurs most frequently in 1700–1800 LST with a secondary peak in 1100–1400 LST,while the tops of precipitation echoes and intense upward air motion reach their highest levels during 1600–1800 LST.The atmospheric conditions in the early morning are disadvantageous for convective initiation and development.Around noon,the convective available potential energy(CAPE)increases markedly,convective inhibition(CIN)is generally small,and a super-dry-adiabatic layer is present near the surface(0–400 m).In the early evening,some larger values of CAPE,level of neutral buoyancy,and total precipitable water are present,suggesting more favorable thermodynamic and water vapor conditions.展开更多
基金supported by the National Key R&D Program of China(Grant No.2018YFC1507200)the National Natural Science Foundation of China(Grant No.41975057).
文摘Based on the previous statistical analysis of mesoscale convective systems(MCSs)over the second-step terrain along Yangtze-Huaihe River Valley,eight representative long-lived eastward-propagating MCSs are selected for model-based sensitivity testing to investigate the initiation and evolution of these types of MCSs as well as their impact on downstream areas.We subject each MCS to a semi-idealized(CNTL)simulation and a sensitivity(NOLH)simulation that neglects condensational heating in the formation region.The CNTL experiment reveals convection forms in the region downstream of a shortwave trough typified by persistent southwesterly winds in the low-to midtroposphere.Upon merging with other convective systems,moist convection develops into an MCS,which propagates eastward under the influence of mid-tropospheric westerlies,and moves out of the second-step terrain.The MCS then merges with pre-existing local convection over the plains;the merged convection reinforces the cyclonic wind perturbation into a mesoscale vortex at 850 hPa.While this vortex moves eastward to regions with local vortex at 850 hPa,another vortex at 925 hPa is also intensified.Finally,the vortices at 850 and 925 hPa merge together and develop into a mesoscale convective vortex(MCV).In contrast,MCSs fail to form and move eastward in the NOLH experiment.In the absence of eastward-propagating MCSs,moist convection and mesoscale vortices still appear in the plains,but the vortex strength and precipitation intensity are significantly weakened.It is suggested the eastward-propagating MCSs over the second-step terrain significantly impact the development and enhancement of moist convection and vortices in the downstream areas.
基金supported by the National Natural Science Foundation of China(Grant Nos.42375008,41975056,42005006)the National Key Scientific and Technological Infrastructure Project“Earth System Numerical Simulation Facility”(EarthLab)the Beijing Municipal Natural Science Foundation(Grant No.8222079)。
文摘Based on the significant weather report,CG lightning,composite radar reflectivity,and ERA5 reanalysis data,we first studied the spatiotemporal distribution characteristics of four types(only severe convective wind(SCW);SCW and hail;SCW and short-duration heavy rainfall(SDHR);and SCW,hail,and SDHR)of convective weather events related to SCW during the warm season(May to September)from 2011 to 2018 in North China.Second,severe convective cases producing SCW were selected to statistically analyze the initiation,decay,lifetime,and organizational characteristics of convective systems.Finally,using ERA5 reanalysis data and conventional surface observation data,preconvective soundings were constructed to explore the differences in environmental conditions for initiating convective systems between SCW and non-SCW.The results indicate that mixed-type of SCW and SDHR events occur more frequently over plains,while other types of convective weather occur more frequently over mountains.The frequency peak of SCW occurs in June,while mixed convective weather peaks in July.The initiation time of convective systems is concentrated between 1000 and 1300 BST,with a peak at 1200 BST.Over mountains,the daily peaks of ordinary and significant SCW generally occur at 1700-1800 BST and 1600-1700 BST,respectively,while over plains,the peak of ordinary SCW typically lags behind that of mountains by 1-2 hours.Additionally,SCW systems are mainly initiated over mountains,with most lifetimes lasting 7–13 hours.Nonlinear convective systems produce the most SCW events,followed by trailing-stratiform convective systems.The convective available potential energy(CAPE),downdraft convective available potential energy,and the temperature difference between 850 and 500 hPa can all distinguish between SCW systems and non-SCW systems occurring over plains.Compared to non-SCW convective systems,SCW convective systems over mountains are more likely to occur in environments with less precipitable water,while SCW convective systems over plains are more likely to occur in environments with higher CAPE and stronger deep-layer wind shear.
基金Sponsored by the National Key Research and Development Program of China(2017YFC1502003 and 2018YFC1507504)National Natural Science Foundation of China(41675045 and 41375051)Strategic Research Projects on Medium-and Long-Term Development of Chinese Engineering Science and Technology(2019-ZCQ-06)。
文摘Located in the Asian monsoon region, China frequently experiences severe convective weather(SCW), such as short-duration heavy rainfall(SDHR), thunderstorm high winds, hails, and occasional tornadoes. Progress in SCW forecasting in China is closely related to the construction and development of meteorological observation networks,especially weather radar and meteorological satellite networks. In the late 1950 s, some county-level meteorological bureaus began to conduct empirical hail forecasting based on observations of clouds and surface meteorological variables. It took over half a century to develop a modern comprehensive operational monitoring and warning system for SCW forecast nationwide since the setup of the first weather radar in 1959. The operational SCW forecasting, including real-time monitoring, warnings valid for tens of minutes, watches valid for several hours, and outlooks covering lead times of up to three days, was established in 2009. Operational monitoring and forecasting of thunderstorms,SDHR, thunderstorm high winds, and hails have been carried out. The performance of operational SCW forecasting will be continually improved in the future with the development of convection-resolving numerical models(CRNMs), the upgrade of weather radar networks, the launch of new-generation meteorological satellites, better understanding of meso-γ and microscale SCW systems, and further application of artificial intelligence technology and CRNM predictions.
基金Supported by the National Natural Science Foundation of China(91437104 and 41605107)Basic Research Funds of the Chinese Academy of Meteorological Sciences(2017Z006)
文摘This study investigates classification and diurnal variations of the precipitation echoes over the central Tibetan Plateau based on the observations collected from a C-band vertically-pointing frequency-modulated continuous-wave(C-FMCW)radar during the Third Tibetan Plateau Atmospheric Scientific Experiment(TIPEX-Ⅲ)2014-Intensive Observation Period(2014-IOP).The results show that 51.32%of the vertical profiles have valid echoes with reflectivity>–10 dBZ,and 35.06% of the valid echo profiles produce precipitation at the ground(precipitation profiles);stratiform precipitation with an evident bright-band signature,weak convective precipitation,and strong convective precipitation account for 52.03%,42.98%,and 4.99% of the precipitation profiles,respectively.About 59.84% of the precipitation occurs in the afternoon to midnight,while 40.16% of the precipitation with weaker intensity is observed in the nocturnal hours and in the morning.Diurnal variation of occurrence frequency of precipitation shows a major peak during 2100–2200 LST(local solar time)with 59.02%being the stratiform precipitation;the secondary peak appears during 1300–1400 LST with 59.71% being the weak convective precipitation;the strong convective precipitation occurs mostly(81.83%)in the afternoon and evening with two peaks over 1200–1300 and 1700–1800 LST,respectively.Starting from approximately 1100 LST,precipitation echoes develop with enhanced vertical air motion,elevated echo top,and increasing radar reflectivity.Intense upward air motion occurs most frequently in 1700–1800 LST with a secondary peak in 1100–1400 LST,while the tops of precipitation echoes and intense upward air motion reach their highest levels during 1600–1800 LST.The atmospheric conditions in the early morning are disadvantageous for convective initiation and development.Around noon,the convective available potential energy(CAPE)increases markedly,convective inhibition(CIN)is generally small,and a super-dry-adiabatic layer is present near the surface(0–400 m).In the early evening,some larger values of CAPE,level of neutral buoyancy,and total precipitable water are present,suggesting more favorable thermodynamic and water vapor conditions.
