Interannual variation of summer precipitation in East China, and frequency of rainstorms during the monsoon season from 1961 to 2010, are analyzed in this study. It is found that the two variables show opposite trends...Interannual variation of summer precipitation in East China, and frequency of rainstorms during the monsoon season from 1961 to 2010, are analyzed in this study. It is found that the two variables show opposite trends on a decadal time scale: frequency of rainstorms increases significantly after the 1990 s, while summer precipitation in East China decreases during the same period. Analysis of the spatial distribution of summer rainstorm frequency from 1961 to 2010 indicates that it decreases from the southeast to the northwest at the east edge of the large-scale topography associated with the plateaus. Spatial distribution of rainstorms with daily rainfall greater than 50 mm is characterized by a "high in the southeast and low in the northwest" pattern, similar to the staircase distribution of the topography. However, the spatial distribution of variation in both summer precipitation and frequency of extreme rainstorms under global warming differs significantly from the three-step staircase topography. It is shown that moisture characteristics of summer precipitation and extreme rainstorms during the monsoon season in East China, including moisture transport pathways, moist flow pattern, and spatial structure of the merging area of moist flows, differ significantly. Areas of frequent rainstorms include the Yangtze River Valley and South China. Column-integrated moisture transport and its spatial structure could be summarized as a "merging" of three branches of intense moist flows from low and middle latitude oceans, and "convergence" of column-integrated moisture fluxes. The merging area for moist flow associated with rainstorms in the high frequency region is located slightly to the south of the monsoonal precipitation or non-rainstorm precipitation, with significantly strong moisture convergence. In addition, the summer moist flow pattern in East China has a great influence on the frequency of extreme rainstorms. Moisture flux vectors in the region of frequent rainstorms correspond to vortical flow pattern. A c展开更多
The coastal eco-city of Fuzhou in Southeastern China has experienced severe ozone(O_(3))episodes at times in recent years.In this study,three typical synoptic circulations types(CTs)that influenced more than 80%of O_(...The coastal eco-city of Fuzhou in Southeastern China has experienced severe ozone(O_(3))episodes at times in recent years.In this study,three typical synoptic circulations types(CTs)that influenced more than 80%of O_(3) polluted days in Fuzhou during 2014-2019 were identified using a subjective approach.The characteristics of meteorological conditions linked to photochemical formation and transport of O_(3) under the three CTs were summarized.Comprehensive Air Quality Model with extensions was applied to simulate O_(3) episodes and to quantify O_(3) sources from different regions in Fuzhou.When Fuzhou was located to the west of a high-pressure system(classified as“East-ridge”),more warm southwesterly currents flowed to Fuzhou,and the effects of cross-regional transport from Guangdong province and high local production promoted the occurrence of O_(3) episodes.Under a uniform pressure field with a low-pressure system occurring to the east of Fuzhou(defined as“East-low”),stagnant weather conditions caused the strongest local production of O_(3) in the atmospheric boundary layer.Controlled by high-pressure systems over the mainland(categorized as“Inland-high”),northerly airflows enhanced the contribution of cross-regional transport to O_(3) in Fuzhou.The abnormal increases of the“East-ridge”and“Inland-high”were closely related to O_(3) pollution in Fuzhou in April and May 2018,resulting in the annual maximum number of O_(3) polluted days during recent years.Furthermore,the rising number of autumn O_(3) episodes in 2017-2019 was mainly related to the“Inland-high”,indicating the aggravation of cross-regional transport and highlighting the necessity of enhanced regional collaboration and efforts in combating O_(3) pollution.展开更多
A record-breaking extreme heavy snowfall(EHS)event hit northern China during 6–8 November 2021,with two maximum snowfall centers in North China(NC)and Northeast China(NEC),which inflicted severe socioeconomic impacts...A record-breaking extreme heavy snowfall(EHS)event hit northern China during 6–8 November 2021,with two maximum snowfall centers in North China(NC)and Northeast China(NEC),which inflicted severe socioeconomic impacts.This paper compares the differences in the synoptic processes and moisture supply associated with the EHS event in NC and NEC,as well as the atmospheric circulation anomalies before the event,to provide a reference for better prediction and forecasting of EHS in northern China.Synoptic analyses show that a positively tilted,inverted 500-hPa trough channeled cold-air outbreaks into NC,while dynamic updrafts along the front below the trough promoted moisture convergence over this region.In NEC,the dynamic updraft south of the frontogenesis region firstly triggered a low-level Yellow–Bohai Sea cyclone,which then converged with the 500-hPa trough to ultimately form an NEC cold vortex.Calculation of the vorticity tendency indicates that absolute vorticity advection was a better indicator than absolute vorticity divergence for the movement of the trough/ridge at the synoptic scale.Moreover,NOAA’s HYSPLIT(Hybrid Single-Particle Lagrangian Integrated Trajectory)model results reveal that the moisture for the EHS over NC mainly originated from the mid-to-low levels over the Asian–African region and the Eurasian mid-to-high latitudes,accounting for 32%and 31%,respectively.In contrast,the source of water vapor for the EHS over NEC was mainly the Eurasian mid-to-high latitudes and East Asia,with contributions of 38%and 28%,respectively.The findings of this study shed some fresh light on the distinctive contributions of different moisture sources to local precipitation.Further analyses of the atmospheric circulation anomalies in October reveal that a phase shift in the Arctic Oscillation related to the weakening of the polar vortex could have served as a useful indicator for the cold-air outbreaks in this EHS event.展开更多
Mesoscale convective systems(MCSs) around the second-step terrain(106°–113°E, 28°–35°N), along the middle reaches of the Yangtze River, were detected, tracked and classified using a black body te...Mesoscale convective systems(MCSs) around the second-step terrain(106°–113°E, 28°–35°N), along the middle reaches of the Yangtze River, were detected, tracked and classified using a black body temperature(TBB) dataset during May to August 2000–2016(except 2005). The MCSs were divided into eastward-propagating(EP) and quasi-stationary(QS) types, to compare their spatial and temporal distributions and convective intensities, and to identify the favorable synoptic conditions for the formation and evolution of EP MCSs. The results showed that both MCS types occurred most often in July. The EP MCSs were mainly initiated over the eastern regions of the study area, while the QS type mainly originated in the western regions of the study area. Both MCS types mainly formed in the afternoon, but a second peak occurred in the early morning for QS MCSs. The EP MCSs had a larger cloud area at their mature stage and a lower cloud brightness temperature, indicating more intense convection. Additionally, the longer lifetime and further eastward propagation of the EP MCSs meant that they had a great influence on the precipitation over the middle and lower reaches of the Yangtze River. Synoptic circulation analysis demonstrated that the combination of the mid-level low trough east of the Tibetan Plateau(TP), and the western pacific subtropical high(WPSH), favored the formation and eastward propagation of EP MCSs. The positive vertical relative vorticity and stronger vertical wind shear provided dynamic conditions favorable for convective organization and development. Furthermore, a stronger low level jet imported warm and moist air to the eastern edge of, and the regions east of, the second-step terrain. The substantial convergence of water vapor promoted the development and long-lived maintenance of the EP MCSs.展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 41130960)the National Science and Technology Pillar Program of China (Grant No. 2012BAK10B04)the National Department of Public Benefit Research Foundation of China (Grant No. GYHY201406001)
文摘Interannual variation of summer precipitation in East China, and frequency of rainstorms during the monsoon season from 1961 to 2010, are analyzed in this study. It is found that the two variables show opposite trends on a decadal time scale: frequency of rainstorms increases significantly after the 1990 s, while summer precipitation in East China decreases during the same period. Analysis of the spatial distribution of summer rainstorm frequency from 1961 to 2010 indicates that it decreases from the southeast to the northwest at the east edge of the large-scale topography associated with the plateaus. Spatial distribution of rainstorms with daily rainfall greater than 50 mm is characterized by a "high in the southeast and low in the northwest" pattern, similar to the staircase distribution of the topography. However, the spatial distribution of variation in both summer precipitation and frequency of extreme rainstorms under global warming differs significantly from the three-step staircase topography. It is shown that moisture characteristics of summer precipitation and extreme rainstorms during the monsoon season in East China, including moisture transport pathways, moist flow pattern, and spatial structure of the merging area of moist flows, differ significantly. Areas of frequent rainstorms include the Yangtze River Valley and South China. Column-integrated moisture transport and its spatial structure could be summarized as a "merging" of three branches of intense moist flows from low and middle latitude oceans, and "convergence" of column-integrated moisture fluxes. The merging area for moist flow associated with rainstorms in the high frequency region is located slightly to the south of the monsoonal precipitation or non-rainstorm precipitation, with significantly strong moisture convergence. In addition, the summer moist flow pattern in East China has a great influence on the frequency of extreme rainstorms. Moisture flux vectors in the region of frequent rainstorms correspond to vortical flow pattern. A c
基金supported by the National Key Research and Development Program of China(Nos.2018YFC0213204,2018YFC0213506).
文摘The coastal eco-city of Fuzhou in Southeastern China has experienced severe ozone(O_(3))episodes at times in recent years.In this study,three typical synoptic circulations types(CTs)that influenced more than 80%of O_(3) polluted days in Fuzhou during 2014-2019 were identified using a subjective approach.The characteristics of meteorological conditions linked to photochemical formation and transport of O_(3) under the three CTs were summarized.Comprehensive Air Quality Model with extensions was applied to simulate O_(3) episodes and to quantify O_(3) sources from different regions in Fuzhou.When Fuzhou was located to the west of a high-pressure system(classified as“East-ridge”),more warm southwesterly currents flowed to Fuzhou,and the effects of cross-regional transport from Guangdong province and high local production promoted the occurrence of O_(3) episodes.Under a uniform pressure field with a low-pressure system occurring to the east of Fuzhou(defined as“East-low”),stagnant weather conditions caused the strongest local production of O_(3) in the atmospheric boundary layer.Controlled by high-pressure systems over the mainland(categorized as“Inland-high”),northerly airflows enhanced the contribution of cross-regional transport to O_(3) in Fuzhou.The abnormal increases of the“East-ridge”and“Inland-high”were closely related to O_(3) pollution in Fuzhou in April and May 2018,resulting in the annual maximum number of O_(3) polluted days during recent years.Furthermore,the rising number of autumn O_(3) episodes in 2017-2019 was mainly related to the“Inland-high”,indicating the aggravation of cross-regional transport and highlighting the necessity of enhanced regional collaboration and efforts in combating O_(3) pollution.
基金Supported by the National Key Research and Development Program of China(2018YFC1505604)Innovation and Development Project of China Meteorological Administration(CXFZ2021J022).
文摘A record-breaking extreme heavy snowfall(EHS)event hit northern China during 6–8 November 2021,with two maximum snowfall centers in North China(NC)and Northeast China(NEC),which inflicted severe socioeconomic impacts.This paper compares the differences in the synoptic processes and moisture supply associated with the EHS event in NC and NEC,as well as the atmospheric circulation anomalies before the event,to provide a reference for better prediction and forecasting of EHS in northern China.Synoptic analyses show that a positively tilted,inverted 500-hPa trough channeled cold-air outbreaks into NC,while dynamic updrafts along the front below the trough promoted moisture convergence over this region.In NEC,the dynamic updraft south of the frontogenesis region firstly triggered a low-level Yellow–Bohai Sea cyclone,which then converged with the 500-hPa trough to ultimately form an NEC cold vortex.Calculation of the vorticity tendency indicates that absolute vorticity advection was a better indicator than absolute vorticity divergence for the movement of the trough/ridge at the synoptic scale.Moreover,NOAA’s HYSPLIT(Hybrid Single-Particle Lagrangian Integrated Trajectory)model results reveal that the moisture for the EHS over NC mainly originated from the mid-to-low levels over the Asian–African region and the Eurasian mid-to-high latitudes,accounting for 32%and 31%,respectively.In contrast,the source of water vapor for the EHS over NEC was mainly the Eurasian mid-to-high latitudes and East Asia,with contributions of 38%and 28%,respectively.The findings of this study shed some fresh light on the distinctive contributions of different moisture sources to local precipitation.Further analyses of the atmospheric circulation anomalies in October reveal that a phase shift in the Arctic Oscillation related to the weakening of the polar vortex could have served as a useful indicator for the cold-air outbreaks in this EHS event.
基金supported by the National Key R & D Program of China (Grants No. 2018YFC1507200)the National Natural Science Foundation of China (Grants Nos. 41505038, 91637211, 41775046 & 41575045)。
文摘Mesoscale convective systems(MCSs) around the second-step terrain(106°–113°E, 28°–35°N), along the middle reaches of the Yangtze River, were detected, tracked and classified using a black body temperature(TBB) dataset during May to August 2000–2016(except 2005). The MCSs were divided into eastward-propagating(EP) and quasi-stationary(QS) types, to compare their spatial and temporal distributions and convective intensities, and to identify the favorable synoptic conditions for the formation and evolution of EP MCSs. The results showed that both MCS types occurred most often in July. The EP MCSs were mainly initiated over the eastern regions of the study area, while the QS type mainly originated in the western regions of the study area. Both MCS types mainly formed in the afternoon, but a second peak occurred in the early morning for QS MCSs. The EP MCSs had a larger cloud area at their mature stage and a lower cloud brightness temperature, indicating more intense convection. Additionally, the longer lifetime and further eastward propagation of the EP MCSs meant that they had a great influence on the precipitation over the middle and lower reaches of the Yangtze River. Synoptic circulation analysis demonstrated that the combination of the mid-level low trough east of the Tibetan Plateau(TP), and the western pacific subtropical high(WPSH), favored the formation and eastward propagation of EP MCSs. The positive vertical relative vorticity and stronger vertical wind shear provided dynamic conditions favorable for convective organization and development. Furthermore, a stronger low level jet imported warm and moist air to the eastern edge of, and the regions east of, the second-step terrain. The substantial convergence of water vapor promoted the development and long-lived maintenance of the EP MCSs.
