Based on Reanalysis datasets from National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) and summer rainfall datasets from China National Climate Center (NCC), by using tren...Based on Reanalysis datasets from National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) and summer rainfall datasets from China National Climate Center (NCC), by using trend analysis and composite analysis methods, the relationship between the reduction of summer precipitation in North China and northern hemispheric circulation changes was investigated. The results show that summer rainfall in North China had a significant decreasing tendency, especially true since 1965 in which an abrupt change occurred. The northern hemisphere atmospheric circulation at 500 hPa had a remarkable change after 1965, from outstanding meridional circulation to outstanding zonal circulation, leading to upper trough activity to decrease, resulting in the rainfall weather processes caused by upward motion behind trough significantly to reduce. At 500 hPa in Mongolian region, air temperature decreased, resulting in lower troposphere pressure to increase, leading to low pressure activity significantly to decrease and rainfall weather processes influencing North China to reduce. At the same time, the decreased air temperature in 500 hPa would caused the upper troposphere geopotential height to reduce, resulting in high–altitude jet southerly location, the East Asian summer monsoon to weaken, then it was difficult for water vapor transport to cross the Yangtze River valley and reach the North China region, with a southerly summer monsoon rainfall zone. The summer precipitation reduction in North China had a good correlation with the northern hemispheric circulation changes.展开更多
In the context of global warming,the extreme summer precipitation over the Tibetan Plateau(TP)has changed significantly.In this study,the summer(June–August)extreme precipitation on the TP was classified into three s...In the context of global warming,the extreme summer precipitation over the Tibetan Plateau(TP)has changed significantly.In this study,the summer(June–August)extreme precipitation on the TP was classified into three spatial types by applying the K-means clustering method to the Third Pole Region long time-series high-resolution(1/30°)precipitation dataset(TPHi Pr,1979–2020).The characteristics of the circulation anomalies and precursors corresponding to the extreme precipitation on the TP in summer during 1979–2020 were investigated.The results showed that the summer extreme precipitation of the TP can be categorized into northwestern(NW),southeastern(SE),and southern Himalayan(HS)types based on extreme precipitation thresholds.The NW and SE types are mainly influenced by anomalous signals in the mid-to-high latitude regions upstream of them,whereas the HS type is controlled by the localized subtropical anomalous circulation.On the 8th day before the onset of the NW type,an anomalous cyclone was observed in the western Atlantic Ocean(60°W,50°N),which triggered the west-to-east quasi-latitudinal propagation of Rossby waves.On the onset day of the NW type,the upper troposphere showed positive-negative-positive geopotential height anomalies along the latitudinal 40°N from the Caspian Sea,the western part of Xinjiang,to the northeastern TP.Moisture entered from the Arabian Sea along the southeastern edge of the anomalous cyclone on the southwestern TP and converged in the northwestern TP.Compared to the NW type,the precursors of the SE type appeared at higher latitudes and were more intense.On the 8th day before the onset of the SE type,an anomalous cyclone occurred near Greenland(60°W,70°N)and excited Rossby waves propagating southeastward.On the onset day of the SE type,the upper troposphere showed negative-positive-negative geopotential height anomalies across Eurasia from the Ural Mountains and the Iranian Plateau to the northern TP in the northwest-southeast direction and entered the southeastern TP from the Bay of Bengal along the southeastern edge of the anomalous cyclone in the southern TP.On the 6th day before the onset of the HS type,the anomalously high pressure in the middle and lower layers of the low-latitude region extended westward,and a significant anticyclonic anomalous circulation occurred on the southern TP on the onset day of the HS type,enabling the delivery of moisture from the Bay of Bengal to the southern foothills of the Himalayas.Additionally,an anomalous cyclone perched in the northeastern TP at a geopotential height of 200 h Pa strengthened westerly winds in the southern TP and contributed to the maintenance of the anticyclonic system on the southern TP.展开更多
Precipitation anomalies in the first raining season of southern China were analyzed,with the suggestion that there are obvious interannual variation of peak values.In the raining season,the general tendency of precipi...Precipitation anomalies in the first raining season of southern China were analyzed,with the suggestion that there are obvious interannual variation of peak values.In the raining season,the general tendency of precipitation is not obvious and the anomalous oscillation is multi-scale.Corresponding to years of more or less precipitation in the raining season,there are sharply opposite distribution across the nation in the simultaneous periods.In addition,by studying the distribution of correlation between anomalous precipitation in southern China in the first raining season and SSTA over offshore waters of China in the preceding period (June ～August of the previous year),a sensitive zone of waters has been found that has steady effect on the precipitation of southern China in the season.Discussions are also made of the sensitive period,its simultaneous SSTA and subsequent anomalous circulation field in relation to precipitation anomalies and simultaneous circulation field in the first raining season of southern China.In the last part of the work,relationship between the SSTA in the sensitive zone and global SSTA is analyzed.A possible mechanism by which SSTA in offshore Chinese waters affects the precipitation anomalies in the first raining season of southern China is put forward.展开更多
The variations of regional mean daily precipitation extreme （RMDPE） events in central China and associated circulation anomalies during June, July, and August （JJA） of 1961-2010 are investigated by using daily in-...The variations of regional mean daily precipitation extreme （RMDPE） events in central China and associated circulation anomalies during June, July, and August （JJA） of 1961-2010 are investigated by using daily in-situ precipitation observations and the NCEP/NCAR reanalysis data. The precipitation data were collected at 239 state-level stations distributed throughout the provinces of Henan, Hubei, and Hunan. During 1961-2010, the 99th percentile threshold for RMDPE is 23.585 mm day-1. The number of RMDPE events varies on both interannual and interdecadal timescales, and increases significantly after the mid 1980s. The RMDPE events happen most frequently between late June and mid July, and are generally associated with anomalous baroclinic tropospheric circulations. The supply of moisture to the southern part of central China comes in a stepping way from the outer-region of an abnormal anticyclone over the Bay of Bengal and the South China Sea. Fluxes of wave activity generated over the northeastern Tibetan Plateau converge over central China, which favors the genesis and maintenance of wave disturbances over the region. RMDPE events typically occur in tandem with a strong heating gradient formed by net heating in central China and the large-scale net cooling in the surrounding area. The occurrence of RMDPE events over central China is tied to anomalous local cyclonic circulations, topographic forcing over the northeast Tibetan Plateau, and anomalous gradients of diabatic heating between central China and the surrounding areas.展开更多
文摘Based on Reanalysis datasets from National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) and summer rainfall datasets from China National Climate Center (NCC), by using trend analysis and composite analysis methods, the relationship between the reduction of summer precipitation in North China and northern hemispheric circulation changes was investigated. The results show that summer rainfall in North China had a significant decreasing tendency, especially true since 1965 in which an abrupt change occurred. The northern hemisphere atmospheric circulation at 500 hPa had a remarkable change after 1965, from outstanding meridional circulation to outstanding zonal circulation, leading to upper trough activity to decrease, resulting in the rainfall weather processes caused by upward motion behind trough significantly to reduce. At 500 hPa in Mongolian region, air temperature decreased, resulting in lower troposphere pressure to increase, leading to low pressure activity significantly to decrease and rainfall weather processes influencing North China to reduce. At the same time, the decreased air temperature in 500 hPa would caused the upper troposphere geopotential height to reduce, resulting in high–altitude jet southerly location, the East Asian summer monsoon to weaken, then it was difficult for water vapor transport to cross the Yangtze River valley and reach the North China region, with a southerly summer monsoon rainfall zone. The summer precipitation reduction in North China had a good correlation with the northern hemispheric circulation changes.
基金upported by the National Natural Science Foundation of China(Grant No.41975090)the Natural Science Foundation of Hunan Province,China(Grant No.2022JJ20043)+1 种基金the Science and Technology Innovation Program of Hunan Province(Grant No.2022RC1239)the Jiangsu Collaborative Innovation Center for Climate Change in Nanjing University。
文摘In the context of global warming,the extreme summer precipitation over the Tibetan Plateau(TP)has changed significantly.In this study,the summer(June–August)extreme precipitation on the TP was classified into three spatial types by applying the K-means clustering method to the Third Pole Region long time-series high-resolution(1/30°)precipitation dataset(TPHi Pr,1979–2020).The characteristics of the circulation anomalies and precursors corresponding to the extreme precipitation on the TP in summer during 1979–2020 were investigated.The results showed that the summer extreme precipitation of the TP can be categorized into northwestern(NW),southeastern(SE),and southern Himalayan(HS)types based on extreme precipitation thresholds.The NW and SE types are mainly influenced by anomalous signals in the mid-to-high latitude regions upstream of them,whereas the HS type is controlled by the localized subtropical anomalous circulation.On the 8th day before the onset of the NW type,an anomalous cyclone was observed in the western Atlantic Ocean(60°W,50°N),which triggered the west-to-east quasi-latitudinal propagation of Rossby waves.On the onset day of the NW type,the upper troposphere showed positive-negative-positive geopotential height anomalies along the latitudinal 40°N from the Caspian Sea,the western part of Xinjiang,to the northeastern TP.Moisture entered from the Arabian Sea along the southeastern edge of the anomalous cyclone on the southwestern TP and converged in the northwestern TP.Compared to the NW type,the precursors of the SE type appeared at higher latitudes and were more intense.On the 8th day before the onset of the SE type,an anomalous cyclone occurred near Greenland(60°W,70°N)and excited Rossby waves propagating southeastward.On the onset day of the SE type,the upper troposphere showed negative-positive-negative geopotential height anomalies across Eurasia from the Ural Mountains and the Iranian Plateau to the northern TP in the northwest-southeast direction and entered the southeastern TP from the Bay of Bengal along the southeastern edge of the anomalous cyclone in the southern TP.On the 6th day before the onset of the HS type,the anomalously high pressure in the middle and lower layers of the low-latitude region extended westward,and a significant anticyclonic anomalous circulation occurred on the southern TP on the onset day of the HS type,enabling the delivery of moisture from the Bay of Bengal to the southern foothills of the Himalayas.Additionally,an anomalous cyclone perched in the northeastern TP at a geopotential height of 200 h Pa strengthened westerly winds in the southern TP and contributed to the maintenance of the anticyclonic system on the southern TP.
文摘Precipitation anomalies in the first raining season of southern China were analyzed,with the suggestion that there are obvious interannual variation of peak values.In the raining season,the general tendency of precipitation is not obvious and the anomalous oscillation is multi-scale.Corresponding to years of more or less precipitation in the raining season,there are sharply opposite distribution across the nation in the simultaneous periods.In addition,by studying the distribution of correlation between anomalous precipitation in southern China in the first raining season and SSTA over offshore waters of China in the preceding period (June ～August of the previous year),a sensitive zone of waters has been found that has steady effect on the precipitation of southern China in the season.Discussions are also made of the sensitive period,its simultaneous SSTA and subsequent anomalous circulation field in relation to precipitation anomalies and simultaneous circulation field in the first raining season of southern China.In the last part of the work,relationship between the SSTA in the sensitive zone and global SSTA is analyzed.A possible mechanism by which SSTA in offshore Chinese waters affects the precipitation anomalies in the first raining season of southern China is put forward.
基金Supported by the National Natural Science Foundation of China(41330425)China Meteorological Administration Special Public Welfare Research Fund(GYHY201406024)
文摘The variations of regional mean daily precipitation extreme （RMDPE） events in central China and associated circulation anomalies during June, July, and August （JJA） of 1961-2010 are investigated by using daily in-situ precipitation observations and the NCEP/NCAR reanalysis data. The precipitation data were collected at 239 state-level stations distributed throughout the provinces of Henan, Hubei, and Hunan. During 1961-2010, the 99th percentile threshold for RMDPE is 23.585 mm day-1. The number of RMDPE events varies on both interannual and interdecadal timescales, and increases significantly after the mid 1980s. The RMDPE events happen most frequently between late June and mid July, and are generally associated with anomalous baroclinic tropospheric circulations. The supply of moisture to the southern part of central China comes in a stepping way from the outer-region of an abnormal anticyclone over the Bay of Bengal and the South China Sea. Fluxes of wave activity generated over the northeastern Tibetan Plateau converge over central China, which favors the genesis and maintenance of wave disturbances over the region. RMDPE events typically occur in tandem with a strong heating gradient formed by net heating in central China and the large-scale net cooling in the surrounding area. The occurrence of RMDPE events over central China is tied to anomalous local cyclonic circulations, topographic forcing over the northeast Tibetan Plateau, and anomalous gradients of diabatic heating between central China and the surrounding areas.
