The dominant patterns of summer rainfall anomalies in East China were studied using Empirical Orthogonal Function （EOF） analysis. The results indicate that after the late 1970s, the first and second dominant pattern...The dominant patterns of summer rainfall anomalies in East China were studied using Empirical Orthogonal Function （EOF） analysis. The results indicate that after the late 1970s, the first and second dominant patterns switched. During the period before the late 1970s, the spatial pattern of the first （second） dominant mode was the ＂Yangtze River pattern＂ （the ＂South China pattern＂）, but this changed to the ＂South China pattern＂ （the ＂Yangtze River pattern＂） after the late 1970s. This decadal change in the dominant patterns resulted from a significant decadal change in summer rainfall over South China after the late 1970s, i.e., a negative phase during 1978-1992 and a positive phase during 1993-2006. When the decadal variation of rainfall in East China is omitted from the analysis, the first and second dominant patterns represent the ＂Yangtze River pattern＂ and the ＂South China pattern＂, respectively. These results suggest that when decadal variation is included, the rainfall in China may be dominated by one mode during certain periods and by another in other periods. For the interannual variability when decadal variation is excluded, however, the first and second modes can be easily distinguished, and their order has been stable since at least 1951.展开更多
Using the monthly summer (June to August) precipitation data over China from 1979 to 1998,and the SST data in Indian Ocean of the overlapping periods,we have analyzed the spatial patterns as well as their temporal evo...Using the monthly summer (June to August) precipitation data over China from 1979 to 1998,and the SST data in Indian Ocean of the overlapping periods,we have analyzed the spatial patterns as well as their temporal evolution of the summer precipitation,along with the relationships between the precipitation over China and the SST in Indian Ocean,with the EOF and SVD methods respectively.The important results are:several canonical anomalous summer precipitation patterns have been identified.The summer SST in Indian Ocean is positively correlated with the simultaneous precipitation in the Yangtze River and Huai River Basin,while negatively with that in other parts of China.展开更多
By applying rotated complex empirical orthogonal function (RCEOF) analysis on 1880-1999 summer rainfall at 28 selected stations over the east part of China, the spatio-temporal variations of China summer rainfall are ...By applying rotated complex empirical orthogonal function (RCEOF) analysis on 1880-1999 summer rainfall at 28 selected stations over the east part of China, the spatio-temporal variations of China summer rainfall are investigated. Six divisions are identified, showing strong temporal variability, the middle and lower reaches of the Yangtze River, the Huaihe River, Southeast China, North China, Southwest China, and Northeast China. The locations of all divisions except Southwest China are in a good agreement with those of the rainband which moves northward from Southeast China to Northeast China from June-August. The phase relationship revealed by the RCEOF analysis suggests that rainfall anomalies in the middle and lower reaches of the Yangtze River, Southeast China, and Northeast China are all characterized by a stationary wave, while a traveling wave is more pronounced in the Huaihe River division, North China, and Southwest China. The fourth RCEOF mode indicates that rainfall anomalies can propagate from south of Northeast China across lower reaches of the Huanghe River and the Huaihe River to the lower reaches of the Yangtze River. A 20-25-year oscillation is found at the middle and lower reaches of the Yangtze River, the Huaihe River valley, North China, and Northeast China. The middle and lower reaches of the Yangtze River and Northeast China also show an approximately-60-year oscillation. Northeast China and the Huaihe River division are dominated by a 36-year and a 70-80-year oscillation, respectively. An 11-year oscillation is also evident in North China, with a periodicity similar to sunspot activity. The interdecadal variability in the middle and lower reaches of the Yangtze River, the Huaihe River valley, and North China shows a significant positive correlation with the solar activity.展开更多
By using NCEP GODAS monthly sea surface height(SSH) and 160-station monthly precipitation data in China,the seasonal and interannual characteristics of SSH are analyzed over the tropical Pacific,and correlations betwe...By using NCEP GODAS monthly sea surface height(SSH) and 160-station monthly precipitation data in China,the seasonal and interannual characteristics of SSH are analyzed over the tropical Pacific,and correlations between SSH and summer rainfall are discussed.The results are shown as follows:(1) The tropical Pacific SSH takes on a "V" pattern in the climatic field with an eastward opening,and it is higher in the western part(in the northwestern part) than in the eastern part(in the southwestern part).The high-value areas are more stable in the northwest,and the value range(greater than 0.8 m) is larger in spring and summer than in autumn and winter.The high-value area in the southwestern part is the largest(smallest) and more northerly(southerly) in spring(summer).SSH is higher in spring and autumn than in summer and winter over the equatorial zone.(2) The interannual anomalies of the SSH are the strongest over the tropical western and southwestern Pacific and are stronger in winter and spring than in summer and autumn.The interannual anomalies are also strong over the equatorial middle and eastern Pacific.The distribution ranges are larger and the intensities are stronger in the autumn and winter.There is a close relationship between the SSH interannual anomalies and ENSO events in autumn,winter and spring.(3) When ENSO events take place in winter,according to the simultaneous relationship among the tropic Pacific SSH,850 hPa wind fields and the summer precipitation of China,it can be predicted that the precipitation will be significantly more than normal over the south of the Yangtze River,especially over Dongting Lake and Poyang Lake region,eastern Qinghai-Tibet Plateau,Yangtze-Huai River Valley,eastern part of Inner Mongolia and less than normal over the area of Great Band of Yellow River,North China and South China in successive summers.展开更多
The second EOF（EOF2） mode of interannual variation in summer rainfall over East China is characterized by inverse rainfall changes between South China（SC） and the Yellow River-Huaihe River valleys（YH）.However,un...The second EOF（EOF2） mode of interannual variation in summer rainfall over East China is characterized by inverse rainfall changes between South China（SC） and the Yellow River-Huaihe River valleys（YH）.However,understanding of the EOF2 mode is still limited.In this study,the authors identify that the EOF2 mode physically depicts the latitudinal variation of the climatological summer-mean rainy belt along the Yangtze River valley（YRRB）,based on a 160-station rainfall dataset in China for the period 1951-2011.The latitudinal variation of the YRRB is mostly attributed to two different rainfall patterns：one reflects the seesaw（SS） rainfall changes between the YH and SC（SS pattern）,and the other features rainfall anomalies concentrated in SC only（SC pattern）.Corresponding to a southward shift of the YRRB,the SS pattern,with above-normal rainfall in SC and below-normal rainfall in the YH,is related to a cyclonic anomaly centered over the SC-East China Sea region,with a northerly anomaly blowing from the YH to SC;while the SC pattern,with above-normal rainfall in SC,is related to an anticyclonic anomaly over the western North Pacific（WNP）,corresponding to an enhanced southwest monsoon over SC.The cyclonic anomaly,related to the SS pattern,is induced by a near-barotropic eastward propagating wave train along the Asian upper-tropospheric westerly jet,originating from the mid-high latitudes of the North Atlantic.The anticyclonic anomaly,for the SC pattern,is related to suppressed rainfall in the WNP.展开更多
Based on the NCEP/NCAR reanalysis data for the period of 1948-2004 and the monthly rainfall data at 160 stations in China from 1951 to 2004, the relationships among the land-ocean temperature anomaly difference in the...Based on the NCEP/NCAR reanalysis data for the period of 1948-2004 and the monthly rainfall data at 160 stations in China from 1951 to 2004, the relationships among the land-ocean temperature anomaly difference in the mid-lower troposphere in spring （April-May）, the mei-yu rainfall in the Yangtze River- Huaihe River basin, and the activities of the South China Sea summer monsoon （SCSSM） are analyzed by using correlation and composite analyses. Results show that a significant positive correlation exists between mei-yu rainfall and air temperature in the middle latitudes above the western Pacific, while a significant negative correlation is located to the southwest of the Baikal Lake. When the land-ocean thermal anomaly difference is stronger in spring, the western Pacific subtropical high （WPSH） will be weaker and retreat eastward in summer （June-July）, and the SCSSM will be stronger and advance further north, resulting in deficient moisture along the mei-yu front and below-normal precipitation in the mid and lower reaches of the Yangtze River, and vice versa for the weaker difference case. The effects and relative importance of the land and ocean anomalous heating on monsoon variability is also compared. It is found that the land and ocean thermal anomalies are both closely related to the summer circulation and mei-yu rainfall and SCSSM intensity, whereas the land heating anomaly is more important than ocean heating in changing the land-ocean thermal contrast and hence the summer monsoon intensity.展开更多
Two types of three-dimensional circulation of the East Asian summer monsoon(EASM) act as the coupling wheels determining the seasonal rainfall anomalies in China during 1979–2015. The first coupling mode features the...Two types of three-dimensional circulation of the East Asian summer monsoon(EASM) act as the coupling wheels determining the seasonal rainfall anomalies in China during 1979–2015. The first coupling mode features the interaction between the Mongolian cyclone over North Asia and the South Asian high(SAH) anomalies over the Tibetan Plateau at 200 hPa. The second mode presents the coupling between the anomalous low-level western Pacific anticyclone and upperlevel SAH via the meridional flow over Southeast Asia. These two modes are responsible for the summer rainfall anomalies over China in 24 and 7 out of 37 years, respectively. However, the dominant SST anomalies in the tropical Pacific, the Indian Ocean, and the North Atlantic Ocean fail to account for the first coupling wheel's interannual variability, illustrating the challenges in forecasting summer rainfall over China.展开更多
In this study, interannual variability of summer rainfall over the northern part of China （NPC） and associated circulation patterns were investigated by using long-term （1961-2013） observational and reanalysis dat...In this study, interannual variability of summer rainfall over the northern part of China （NPC） and associated circulation patterns were investigated by using long-term （1961-2013） observational and reanalysis data. Two important NPC rainfall modes were identified by empirical orthogoual function analysis： the first is characterized by an almost uniformly distributed rainfall anomaly over most parts of the NPC, while the second shows rainfall variability in Northeast China （NEC） and its out-of-phase relationship with that in North China （NC） and the northern part of Northwest China. The results also suggest that the NPC summer rainfall anomalies are also closely associated with those in some other parts of China. It is revealed that the circumglobal teleconnection pattern associated with the anomalous Indian summer monsoon （ISM） and the Polar/Eurasia （PEA） pattern work in concert to constitute the typical circulation pattern of the first rainfall mode. The cooperative engagement of the anomalous ISM circulation and the PEA pattern is fundamental in transporting water vapor to the NPC. The study emphasizes that the PEA pattern is essential for the water vapor transport to the NPC through the anomalous midlatitude westerly. In the second NPC rainfall mode, the typical circulation pattern is characterized by the anomalous surface Okhotsk high and the attendant lower tropospheric circulation anomaly over NEC. The circulation anomaly over NEC leads to a redistribution of water vapor fluxes over the NPC and constitutes an out-of-phase relationship between the rainfall anomalies over NEC and NC.展开更多
Based on three reanalysis datasets—ERA-Interim,NCAR–NCEP and JRA-55—the classification of25 commonly used indexes of the East Asian summer monsoon(EASM)was investigated.The physical nature of two categories of mons...Based on three reanalysis datasets—ERA-Interim,NCAR–NCEP and JRA-55—the classification of25 commonly used indexes of the East Asian summer monsoon(EASM)was investigated.The physical nature of two categories of monsoon index,together with their circulation pattern,climate anomalies,and driving factors,were investigated.Results suggest that the selected 25 monsoon indexes can be classified into two typical categories(CategoryⅠandⅡ),which are dominated by interannual and decadal variabilities of the EASM,respectively.The anomalous circulation patterns and summer rainfall patterns related to the two categories of index also exhibit evident differences.CategoryⅠis closely linked to the low-latitude circulation system and the anomalous circulation pattern is a typical East Asia–Pacific teleconnection pattern.The summer rainfall anomaly exhibits a typical tripole pattern.However,CategoryⅡmainly reflects the impacts of the middle–high latitude circulation system on the summer monsoon and is closely linked to a typical Eurasian teleconnection pattern,which corresponds to a dipole of summer rainfall anomalies.Further analysis suggests that the underlying thermal driving factors of the two categories of monsoon are distinct.The main driving factors of CategoryⅠare the tropical sea surface temperature anomalies(SSTAs),especially ENSO-related SSTAs in the preceding winter and summer SSTAs in the tropical Indian Ocean.The winter signal of Category II summer monsoon anomalous activity mainly originates from the polar region and the middle and high latitudes of the Eurasian continent.CategoryⅡmonsoon activity is also associated with summer SSTAs in the equatorial central Pacific.展开更多
采用1961—2010年NCEP/NCAR逐日再分析资料和台站观测降水量资料,按一定标准选取了华南前汛期24个持续暴雨过程;并且按基本判据确定逐年华南夏季风降水开始日期。然后依据南亚高压环流型和相对于该年夏季风降水开始的早晚,将这些暴雨过...采用1961—2010年NCEP/NCAR逐日再分析资料和台站观测降水量资料,按一定标准选取了华南前汛期24个持续暴雨过程;并且按基本判据确定逐年华南夏季风降水开始日期。然后依据南亚高压环流型和相对于该年夏季风降水开始的早晚,将这些暴雨过程划分为夏季风降水前、后南亚高压东部型,夏季风降水后南亚高压带状、西部型共4个类型;其中,夏季风后南亚高压西部型次数最多、平均持续时间最长。所有类型持续暴雨的相同点是:广东东北部附近均为暴雨频率和雨量高值区;暴雨期间华南150 h Pa位势高度增加、500 h Pa位势高度减少;华南处在150 h Pa偏西风急流南侧辐散区中;850 h Pa华南沿海有明显的西南气流,低层辐合在华南东北部最明显;两广沿海为可降水量大值区;华南的整层水汽输送主要呈现西南向。不同点是:夏季风后南亚高压西部型平均雨量较小,夏季风后南亚高压带状型与西部型在印度洋上存在明显的偏东风高空急流;夏季风后南亚高压类型在两广沿海的可降水量数值较大。展开更多
基金supported by the National Basic Research Program of China(Grant No.2009CB421400)the Ministry of Finance of China(Grant Nos.GYHY201006021and GYHY200906017)
文摘The dominant patterns of summer rainfall anomalies in East China were studied using Empirical Orthogonal Function （EOF） analysis. The results indicate that after the late 1970s, the first and second dominant patterns switched. During the period before the late 1970s, the spatial pattern of the first （second） dominant mode was the ＂Yangtze River pattern＂ （the ＂South China pattern＂）, but this changed to the ＂South China pattern＂ （the ＂Yangtze River pattern＂） after the late 1970s. This decadal change in the dominant patterns resulted from a significant decadal change in summer rainfall over South China after the late 1970s, i.e., a negative phase during 1978-1992 and a positive phase during 1993-2006. When the decadal variation of rainfall in East China is omitted from the analysis, the first and second dominant patterns represent the ＂Yangtze River pattern＂ and the ＂South China pattern＂, respectively. These results suggest that when decadal variation is included, the rainfall in China may be dominated by one mode during certain periods and by another in other periods. For the interannual variability when decadal variation is excluded, however, the first and second modes can be easily distinguished, and their order has been stable since at least 1951.
文摘Using the monthly summer (June to August) precipitation data over China from 1979 to 1998,and the SST data in Indian Ocean of the overlapping periods,we have analyzed the spatial patterns as well as their temporal evolution of the summer precipitation,along with the relationships between the precipitation over China and the SST in Indian Ocean,with the EOF and SVD methods respectively.The important results are:several canonical anomalous summer precipitation patterns have been identified.The summer SST in Indian Ocean is positively correlated with the simultaneous precipitation in the Yangtze River and Huai River Basin,while negatively with that in other parts of China.
基金The authors wish to thank Professor Wang Shaowu from the Department of AtmosphericSciences of Peking University, who generously provided the China Summer Rainfall Station Data used in this study. This research was supported by the National Key Program
文摘By applying rotated complex empirical orthogonal function (RCEOF) analysis on 1880-1999 summer rainfall at 28 selected stations over the east part of China, the spatio-temporal variations of China summer rainfall are investigated. Six divisions are identified, showing strong temporal variability, the middle and lower reaches of the Yangtze River, the Huaihe River, Southeast China, North China, Southwest China, and Northeast China. The locations of all divisions except Southwest China are in a good agreement with those of the rainband which moves northward from Southeast China to Northeast China from June-August. The phase relationship revealed by the RCEOF analysis suggests that rainfall anomalies in the middle and lower reaches of the Yangtze River, Southeast China, and Northeast China are all characterized by a stationary wave, while a traveling wave is more pronounced in the Huaihe River division, North China, and Southwest China. The fourth RCEOF mode indicates that rainfall anomalies can propagate from south of Northeast China across lower reaches of the Huanghe River and the Huaihe River to the lower reaches of the Yangtze River. A 20-25-year oscillation is found at the middle and lower reaches of the Yangtze River, the Huaihe River valley, North China, and Northeast China. The middle and lower reaches of the Yangtze River and Northeast China also show an approximately-60-year oscillation. Northeast China and the Huaihe River division are dominated by a 36-year and a 70-80-year oscillation, respectively. An 11-year oscillation is also evident in North China, with a periodicity similar to sunspot activity. The interdecadal variability in the middle and lower reaches of the Yangtze River, the Huaihe River valley, and North China shows a significant positive correlation with the solar activity.
基金Specific Project on Public Fields (GYHY201006038,GYHY201006020)"973" Program(2013CB430202,2012CB417205)+1 种基金Third-level Talent Training Project of the fourth "333 project" in Jiangsu Provincea project by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘By using NCEP GODAS monthly sea surface height(SSH) and 160-station monthly precipitation data in China,the seasonal and interannual characteristics of SSH are analyzed over the tropical Pacific,and correlations between SSH and summer rainfall are discussed.The results are shown as follows:(1) The tropical Pacific SSH takes on a "V" pattern in the climatic field with an eastward opening,and it is higher in the western part(in the northwestern part) than in the eastern part(in the southwestern part).The high-value areas are more stable in the northwest,and the value range(greater than 0.8 m) is larger in spring and summer than in autumn and winter.The high-value area in the southwestern part is the largest(smallest) and more northerly(southerly) in spring(summer).SSH is higher in spring and autumn than in summer and winter over the equatorial zone.(2) The interannual anomalies of the SSH are the strongest over the tropical western and southwestern Pacific and are stronger in winter and spring than in summer and autumn.The interannual anomalies are also strong over the equatorial middle and eastern Pacific.The distribution ranges are larger and the intensities are stronger in the autumn and winter.There is a close relationship between the SSH interannual anomalies and ENSO events in autumn,winter and spring.(3) When ENSO events take place in winter,according to the simultaneous relationship among the tropic Pacific SSH,850 hPa wind fields and the summer precipitation of China,it can be predicted that the precipitation will be significantly more than normal over the south of the Yangtze River,especially over Dongting Lake and Poyang Lake region,eastern Qinghai-Tibet Plateau,Yangtze-Huai River Valley,eastern part of Inner Mongolia and less than normal over the area of Great Band of Yellow River,North China and South China in successive summers.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41375086 and 41320104007)
文摘The second EOF（EOF2） mode of interannual variation in summer rainfall over East China is characterized by inverse rainfall changes between South China（SC） and the Yellow River-Huaihe River valleys（YH）.However,understanding of the EOF2 mode is still limited.In this study,the authors identify that the EOF2 mode physically depicts the latitudinal variation of the climatological summer-mean rainy belt along the Yangtze River valley（YRRB）,based on a 160-station rainfall dataset in China for the period 1951-2011.The latitudinal variation of the YRRB is mostly attributed to two different rainfall patterns：one reflects the seesaw（SS） rainfall changes between the YH and SC（SS pattern）,and the other features rainfall anomalies concentrated in SC only（SC pattern）.Corresponding to a southward shift of the YRRB,the SS pattern,with above-normal rainfall in SC and below-normal rainfall in the YH,is related to a cyclonic anomaly centered over the SC-East China Sea region,with a northerly anomaly blowing from the YH to SC;while the SC pattern,with above-normal rainfall in SC,is related to an anticyclonic anomaly over the western North Pacific（WNP）,corresponding to an enhanced southwest monsoon over SC.The cyclonic anomaly,related to the SS pattern,is induced by a near-barotropic eastward propagating wave train along the Asian upper-tropospheric westerly jet,originating from the mid-high latitudes of the North Atlantic.The anticyclonic anomaly,for the SC pattern,is related to suppressed rainfall in the WNP.
基金supported by the National Basic Research Program ofChina (Grant No. 2004CB418300)the National Natural Science Foundation of China (Grant No. 40675042)
文摘Based on the NCEP/NCAR reanalysis data for the period of 1948-2004 and the monthly rainfall data at 160 stations in China from 1951 to 2004, the relationships among the land-ocean temperature anomaly difference in the mid-lower troposphere in spring （April-May）, the mei-yu rainfall in the Yangtze River- Huaihe River basin, and the activities of the South China Sea summer monsoon （SCSSM） are analyzed by using correlation and composite analyses. Results show that a significant positive correlation exists between mei-yu rainfall and air temperature in the middle latitudes above the western Pacific, while a significant negative correlation is located to the southwest of the Baikal Lake. When the land-ocean thermal anomaly difference is stronger in spring, the western Pacific subtropical high （WPSH） will be weaker and retreat eastward in summer （June-July）, and the SCSSM will be stronger and advance further north, resulting in deficient moisture along the mei-yu front and below-normal precipitation in the mid and lower reaches of the Yangtze River, and vice versa for the weaker difference case. The effects and relative importance of the land and ocean anomalous heating on monsoon variability is also compared. It is found that the land and ocean thermal anomalies are both closely related to the summer circulation and mei-yu rainfall and SCSSM intensity, whereas the land heating anomaly is more important than ocean heating in changing the land-ocean thermal contrast and hence the summer monsoon intensity.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41830969, 41775052, 42005011, 41776023 and 42076020)the National Key R&D Program (Grant No. 2018YFC1505904)+3 种基金the Scientific Development Foundation of the Chinese Academy of Meteorological Sciences (CAMS) (Grant No. 2020KJ012 and 2020KJ009)the Basic Scientific Research and Operation Foundation of CAMS (Grant Nos. 2018Z006)Youth Innovation Promotion Association CAS (Grant No. 2020340)supported by the Jiangsu Collaborative Innovation Center for Climate Change。
文摘Two types of three-dimensional circulation of the East Asian summer monsoon(EASM) act as the coupling wheels determining the seasonal rainfall anomalies in China during 1979–2015. The first coupling mode features the interaction between the Mongolian cyclone over North Asia and the South Asian high(SAH) anomalies over the Tibetan Plateau at 200 hPa. The second mode presents the coupling between the anomalous low-level western Pacific anticyclone and upperlevel SAH via the meridional flow over Southeast Asia. These two modes are responsible for the summer rainfall anomalies over China in 24 and 7 out of 37 years, respectively. However, the dominant SST anomalies in the tropical Pacific, the Indian Ocean, and the North Atlantic Ocean fail to account for the first coupling wheel's interannual variability, illustrating the challenges in forecasting summer rainfall over China.
基金Supported by the National Natural Science Foundation of China(41375064 and 41630424)National Science and Technology Support Program of China(2015BAC03B03)
文摘In this study, interannual variability of summer rainfall over the northern part of China （NPC） and associated circulation patterns were investigated by using long-term （1961-2013） observational and reanalysis data. Two important NPC rainfall modes were identified by empirical orthogoual function analysis： the first is characterized by an almost uniformly distributed rainfall anomaly over most parts of the NPC, while the second shows rainfall variability in Northeast China （NEC） and its out-of-phase relationship with that in North China （NC） and the northern part of Northwest China. The results also suggest that the NPC summer rainfall anomalies are also closely associated with those in some other parts of China. It is revealed that the circumglobal teleconnection pattern associated with the anomalous Indian summer monsoon （ISM） and the Polar/Eurasia （PEA） pattern work in concert to constitute the typical circulation pattern of the first rainfall mode. The cooperative engagement of the anomalous ISM circulation and the PEA pattern is fundamental in transporting water vapor to the NPC. The study emphasizes that the PEA pattern is essential for the water vapor transport to the NPC through the anomalous midlatitude westerly. In the second NPC rainfall mode, the typical circulation pattern is characterized by the anomalous surface Okhotsk high and the attendant lower tropospheric circulation anomaly over NEC. The circulation anomaly over NEC leads to a redistribution of water vapor fluxes over the NPC and constitutes an out-of-phase relationship between the rainfall anomalies over NEC and NC.
基金supported by the National Natural Science Foundation of China [grant number 41625019]
文摘Based on three reanalysis datasets—ERA-Interim,NCAR–NCEP and JRA-55—the classification of25 commonly used indexes of the East Asian summer monsoon(EASM)was investigated.The physical nature of two categories of monsoon index,together with their circulation pattern,climate anomalies,and driving factors,were investigated.Results suggest that the selected 25 monsoon indexes can be classified into two typical categories(CategoryⅠandⅡ),which are dominated by interannual and decadal variabilities of the EASM,respectively.The anomalous circulation patterns and summer rainfall patterns related to the two categories of index also exhibit evident differences.CategoryⅠis closely linked to the low-latitude circulation system and the anomalous circulation pattern is a typical East Asia–Pacific teleconnection pattern.The summer rainfall anomaly exhibits a typical tripole pattern.However,CategoryⅡmainly reflects the impacts of the middle–high latitude circulation system on the summer monsoon and is closely linked to a typical Eurasian teleconnection pattern,which corresponds to a dipole of summer rainfall anomalies.Further analysis suggests that the underlying thermal driving factors of the two categories of monsoon are distinct.The main driving factors of CategoryⅠare the tropical sea surface temperature anomalies(SSTAs),especially ENSO-related SSTAs in the preceding winter and summer SSTAs in the tropical Indian Ocean.The winter signal of Category II summer monsoon anomalous activity mainly originates from the polar region and the middle and high latitudes of the Eurasian continent.CategoryⅡmonsoon activity is also associated with summer SSTAs in the equatorial central Pacific.
文摘采用1961—2010年NCEP/NCAR逐日再分析资料和台站观测降水量资料,按一定标准选取了华南前汛期24个持续暴雨过程;并且按基本判据确定逐年华南夏季风降水开始日期。然后依据南亚高压环流型和相对于该年夏季风降水开始的早晚,将这些暴雨过程划分为夏季风降水前、后南亚高压东部型,夏季风降水后南亚高压带状、西部型共4个类型;其中,夏季风后南亚高压西部型次数最多、平均持续时间最长。所有类型持续暴雨的相同点是:广东东北部附近均为暴雨频率和雨量高值区;暴雨期间华南150 h Pa位势高度增加、500 h Pa位势高度减少;华南处在150 h Pa偏西风急流南侧辐散区中;850 h Pa华南沿海有明显的西南气流,低层辐合在华南东北部最明显;两广沿海为可降水量大值区;华南的整层水汽输送主要呈现西南向。不同点是:夏季风后南亚高压西部型平均雨量较小,夏季风后南亚高压带状型与西部型在印度洋上存在明显的偏东风高空急流;夏季风后南亚高压类型在两广沿海的可降水量数值较大。
