The tropical Indian Ocean (TIO) is warmer than normal during the summer when or after the El Nio decays. The present study investigates the impact of TIO SST on the South Asian High (SAH) in summer. When the TIO is ...The tropical Indian Ocean (TIO) is warmer than normal during the summer when or after the El Nio decays. The present study investigates the impact of TIO SST on the South Asian High (SAH) in summer. When the TIO is warmer, the SAH strengthens and its center shifts southward. It is found that the variations in the SAH cannot be accounted for by the precipitation anomaly. A possible mechanism is proposed to explain the connection between the TIO and SAH: warmer SST in the TIO changes the equivalent potential temperature (EPT) in the atmospheric boundary layer (ABL), alters the temperature profile of the moist atmosphere, warms the troposphere, which produces significant positive height anomaly over South Asia and modifies the SAH. An atmospheric general circulation model, ECHAM5, which has a reasonable prediction skill in the TIO and South Asia, was selected to test the effects of TIO SST on the SAH. The experiment with idealized heating over the TIO reproduced the response of the SAH to TIO warming. The results suggest that the TIO-induced EPT change in the ABL can account for the variations in the SAH.展开更多
A case is reported, during which the Subtropical High over the Western Pacific (hereafter, SHWP in abbreviation) shifted northwestward and met-yu at Chaniiang River valley ended. Several numerical experiments onSHWP a...A case is reported, during which the Subtropical High over the Western Pacific (hereafter, SHWP in abbreviation) shifted northwestward and met-yu at Chaniiang River valley ended. Several numerical experiments onSHWP activity influenced by the heating over south Asia monsoon area are carried out, and the statistic significance of the results is checked. The results indicate that the enhancement of positive heating over South Asia willmotivate a wave-like series of anomaly centers, which propagate northeastward from the maximum heating center.so that a strong positive potential height anomaly center will set up from North China to Japan at Day X resultingin the enhancement of SHWP. Comparison of the influence upon SHWP by the heating over south Asia monsoonarea with that over ITCZ area south to SHWP is also carried out. It is pointed out that the heating over South Asiamonsoon area tends to favor SHWP north\vard movement while the heating over ITCZ area tends to thvor SHWPwestward stretching. As for the time to begin to influence on SHWP, the heating over south Asia monsoon areafavors the enhancement of SHWP atter Day 3 while that over ITCZ south to SHWP effects atter Day 5.展开更多
[Objective] The aim was to study the relation among summer rainfall in south Shandong and high pressure in South Asia and atmospheric circulation.[Method] Taking the precipitation in south Shandong along the Yellow Ri...[Objective] The aim was to study the relation among summer rainfall in south Shandong and high pressure in South Asia and atmospheric circulation.[Method] Taking the precipitation in south Shandong along the Yellow River and Huaihe River,using the NCEP/NCAR data and summer rainfall data in south Shandong in summer from 1961 to 2005,the characteristics of high pressure in South Asia and atmospheric circulation in drought year and flood year in summer in south Shandong Province were expounded.The mechanism of 100 hPa pressure in South Asian influencing precipitation in south Shandong Province was discussed.The interaction of different equipment,different altitude and different system of atmosphere circulation in low and high layer was expounded.[Results] The first mode of EOF decomposition of precipitation in summer in south Shandong Province explained above 63% variances and reflected universal form of precipitation.The difference of central position of the central position of height field of high pressure in South Asia in drought and flood year was small.But the wind field center was inconsistent.As the area of SAH was smaller and its eastern ridge line stretched to the Western Pacific between the middle of south Shandong and Changjiang Estuary,flood summer occurred when there was an unusual cyclone lied in the east of 90° E and south of Lake Baikal.The area of SAH was larger and its eastern ridge line stretching to the Western Pacific over Changjiang Estuary,drought summer occurred,when there was an unusual anticyclone lied in the east of 90° E and south of Lake Baikal.SAH and summer rainfall also had close relationship with Tele-connection Patterns over the Eurasia continent and EAP Tele-connection.When the height anomaly was in "+-+" form in the north of the Caspian Sea,around Lake Baikal and Kamchatka,and when the height anomaly in East Asia-West Pacific area was in "-+" form from low altitude to high altitude,there was much precipitation in summer;and conversely,it was drought in summer in south Shandong.[Conclusion] It provided the oretical basis for summer rainfall in south Shandong.展开更多
Comparisons of the west Pacific subtropical high with the South Asia High are made using the NCEP/NCAR and ECMWF 500 hPa and 100 hPa monthly boreal geopotential height fields for the period 1961-2000. Discrepancies ar...Comparisons of the west Pacific subtropical high with the South Asia High are made using the NCEP/NCAR and ECMWF 500 hPa and 100 hPa monthly boreal geopotential height fields for the period 1961-2000. Discrepancies are found for the time prior to 1980. The west Pacific subtropical high in the NCEP/NCAR data is less intense than in ECMWF data before 1980. The range and strength of the west Pacific subtropical high variation described by the NCEP/NCAR data are larger than those depicted by ECMWF data. The same situation appears in the 100-hPa geopotential field. These discoveries suggest that the interdecadal variation of the two systems as shown by the NCEP/NCAR data may not be true. Besides, the South Asia High center in the NCEP/NCAR data is obviously stronger than in the ECMWF data during the periods 1969, 1979-1991 and 1992-1995. Furthermore, the range is larger from 1992 to 1995.展开更多
By analyzing the change of an index for the characteristics of South Asia High and variations of upper-air troughs in 2002–2005,we studied the impact of South Asia high on the beginning and ending of the Mei-yu(i.e.s...By analyzing the change of an index for the characteristics of South Asia High and variations of upper-air troughs in 2002–2005,we studied the impact of South Asia high on the beginning and ending of the Mei-yu(i.e.sustained rain corresponding to the ripening season of plum)in Jiangsu province.Statistic verification is conducted on the relationships between the index and the Mei-yu season in 1991–2005 to examine the impacts of the SAH characteristics index on a rain intensity index of Mei-yu and regional distribution of a characteristics index for different annual patterns of Mei-yu.Historical composite is performed of the 100-hPa circulation field for these patterns using the 100-hPa geopotential height of Northern Hemisphere from 2002 to 2005 and 45-year NCEP reanalysis to study the difference in the circulation for different patterns of Mei-yu.Diagnostic and statistic conclusions,which share much in common,have been obtained as follows.(1)The characteristics preceding to and the advancement/retreat of SAH and the movement of westerly troughs are the factors that influence the onset time of the Mei-yu season;after the Mei-yu onset,the progression/withdrawal of SAH and how farther east it extends are determining how long the Mei-yu lasts and when it ends.(2)During the Mei-yu,the general 100-hPa circulation situation and average characteristics of the SAH are well corresponding to the characteristics of the season and annual patterns of Mei-yu.In addition,the averages of the SAH ridgeline and east-extending index for June,July and the Mei-yu season have some implications to the forecast of the index of Mei-yu intensity.These conclusions can be served as powerful means in determining the starting/ending dates, duration and annual pattern of the Mei-yu season.展开更多
The NCEP 1°×1°reanalysis of June-to-September dataset between 2002 to 2009 is used in this study to conduct statistical analysis of the relationship between the environmental potential vorticity(PV)on 1...The NCEP 1°×1°reanalysis of June-to-September dataset between 2002 to 2009 is used in this study to conduct statistical analysis of the relationship between the environmental potential vorticity(PV)on 150 hPa located at the south edge of South Asia High(SAH)and TCs making landfall.The results show that 23 of the TCs are affected by the PV on 150 hPa located at the south edge of SAH between 2002 to2009,and three TCs'center pressure decline after the high-value environmental PV moves to the center of the TCs.These three TCs are Senlaku(0216),Bilis(0604)and Linfa(0903).Through diagnostic analysis from the viewpoint of isolines,we determined the relationship between the intensification of these TCs and the PV anomaly at high levels;the isentropic surface is close to the high level’s PV anomaly under the influence of the 150-hPa PV anomaly,leading to the decline of isentropic surfaces on both sides of the PV anomaly.Then the warm core of the middle and high levels of the TC strengthens and PV increases at the middle level,and both of them are beneficial to the reinforcement of the cyclonic vorticity in the low level.As a result,the center pressure of the TC declines.According to Wu’s theory of Slantwise Vorticity Development(SVD),the incline of the isentropic surfaces leads to the development of vertical vorticity,contributing to the vertical motion and the release of the latent heat.Then the warm core of the TC strengthens and the TC strengthens,too.Otherwise,piecewise PV inversion also shows that the high-level PV influences the mid-level more than the low level.展开更多
NCEP/NCAR data are utilized to analyze an extreme flood year(1998) and an extreme dry year(2006) in the Sichuan-Chongqing region(SCR) and the results are as follows. The positive divergence of South Asia High(SAH) is ...NCEP/NCAR data are utilized to analyze an extreme flood year(1998) and an extreme dry year(2006) in the Sichuan-Chongqing region(SCR) and the results are as follows. The positive divergence of South Asia High(SAH) is stronger in the flood year; the position of the ridge line of SAH is southward compared with the annual average; Western Pacific Subtropical High(WPSH) extends westward and its ridge line is southward. In the drought year, the positive divergence of SAH is weaker, its ridge line is northward, and the position of WPSH is also northward. As shown in the dynamics, in drought(flood) years, negative(positive) vorticity advection in the upper atmosphere can cause the atmosphere to ascend(descend), and anomalous circulation of SAH displays divergence(convergence), and anomalous circulation of the lower atmosphere shows convergence(divergence). Thermal structure of the atmosphere shows that there is warm(cold) temperature advection in the lower atmosphere, and the vertical distribution of diabetic heating causes SAH's local circulation to display convergence(divergence) and affects vertical motion of the lower atmosphere circulation eventually. To some extent, the two extreme years in the SCR is closely related to the vertical motion of atmosphere circulation and the variation of such vertical motion is caused by differences of interactions between SAH and lower atmosphere circulations.展开更多
The characteristics of the South Asia high (SAH) and subtropical westerly jets in the summer of 2010 and their relationship with the changes in rainband in China were analyzed. As shown by the results, the SAH in the ...The characteristics of the South Asia high (SAH) and subtropical westerly jets in the summer of 2010 and their relationship with the changes in rainband in China were analyzed. As shown by the results, the SAH in the upper troposphere extended northward relatively late in June 2010. Correspondingly, the subtropical westerly jets on the north side of the SAH jumped northward comparatively late, thus delaying the formation of a strong divergence field in the upper air over the Yangtze-Huaihe River valley. This was one of the main causes for the late onset of plum rains in the Yangtze-Huaihe River valley. In July, there was a vertical structure consisting of upper-level divergence and low-level convergence near the subtropical westerly jets on the north side of the SAH and in the air stream dispersal area on the northeast side of the eastward-extending SAH, which was the dynamic mechanism bringing about frequent and extremely heavy rainstorms during the plum rain period in this year. The SAH in the upper troposphere affected the subtropical high in the lower stratosphere, and thereby led to changes in the main rainband location in China.展开更多
In the context of 1958-1997 NCFP NCAR re-analyses, the South Asia high (SAH) was divided into two components, barotropic and haroclinic, the former based on mass weighed vertical integration and the latter on the diff...In the context of 1958-1997 NCFP NCAR re-analyses, the South Asia high (SAH) was divided into two components, barotropic and haroclinic, the former based on mass weighed vertical integration and the latter on the difference between the measured circulation and the barotropic component counterpart, whereupon the barotropic and baroclinic circulation conversion features were addressed of the research SAH during its seasonal variation. Evidence suggests that i) in summer (winter). the SAH is a thermal (dynamical) system. with dominant baroclinicity (barotropicity). either of the components accounting for approximately 70% of the total contribution; ii) as time progresses from winter to summer, accompanied by the barotropic SAH evolving into its baroclinic analog, the SAH is moving under the" thermal guidance" of its baroclinic component circulation, suggesting that the component circulation precedes the system itself in variation. iii) the reversal happens when it goes from summer to winter, with the SAH displacement under the" dynamic steering" of its barotropic component circulation.展开更多
基于美国国家海洋和大气管理局(National Oceanic and Atmospheric Administration, NOAA)全球范围扩展重建海面温度资料第5版本(Extended Reconstructed Sea Surface Temperature version 5,ERSSTv5),以及美国国家环境预报中心和国家...基于美国国家海洋和大气管理局(National Oceanic and Atmospheric Administration, NOAA)全球范围扩展重建海面温度资料第5版本(Extended Reconstructed Sea Surface Temperature version 5,ERSSTv5),以及美国国家环境预报中心和国家大气研究中心NCEP(National Centers for Environmental Prediction)/NCAR(National Center for Atmospheric Research)逐月全球再分析资料,采用相关、回归、合成及物理量诊断等方法,对2022年夏季中国大范围高温相关环流异常的可能成因进行了分析。结果表明:(1)2022年夏季南亚高压偏强并分别向东、西方向扩展,西太平洋副热带高压(以下简称“副高”)异常偏强西伸。2022夏季为拉尼娜(La Nina)年,但热带大西洋垂直上升环流相对西太平洋更强,且热带印度洋到西太平洋热带垂直上升环流异常也偏强。(2)2022年热带大西洋、印度洋到西太平洋上空垂直环流异常和La Nina共同作用,使得夏季南亚高压和西太平洋副高极端异常。La Nina和印度洋到西太平洋垂直环流异常有利于南亚高压和西太平洋副高的偏强西伸;热带大西洋环流异常则既有利于南亚高压的加强及东扩,也有利于西太平洋副高偏强西伸。(3)印度洋到西太平洋垂直环流主要通过局地经向哈得来(Hadley)环流影响青藏高原到中国东部的环流异常,表现为青藏高原到中国东部中低层为显著的辐散异常;热带大西洋则通过引起纬向风异常(急流异常),激发遥相关波列并向下游传播,进而影响青藏高原到中国东部地区的环流异常。展开更多
利用1961—2022年四川155个国家气象站逐日气温、降水资料和NCEP/NCAR再分析资料等,对2022年四川持续高温干旱事件特征及成因进行分析。结果表明:2022年夏季四川出现极端高温干旱天气,全省平均气温、最高气温、高温日数均突破历史同期极...利用1961—2022年四川155个国家气象站逐日气温、降水资料和NCEP/NCAR再分析资料等,对2022年四川持续高温干旱事件特征及成因进行分析。结果表明:2022年夏季四川出现极端高温干旱天气,全省平均气温、最高气温、高温日数均突破历史同期极值,73.0%的站点出现重旱及以上旱情,为1961年以来最严重高温伏旱天气气候事件。南亚高压北跳东进,异常偏强偏北,500 h Pa青藏高压发展东移,或西太平洋副热带高压加强西伸北抬,与南亚高压叠加,形成稳定正压结构控制四川,是造成高温干旱的主要原因。亚洲中纬度地区盛行纬向环流,伊朗高压、青藏高压和西太平洋副热带高压打通形成高压带,盛行下沉辐散气流,阻挡中高纬冷空气南下和低纬暖湿气流北上,导致四川地区降水异常偏少,是高温干旱的间接原因。展开更多
基金supported by the National Key Technology R&D Program 2008BAK50B02CAS Innovation Key Program (Grant No. KZCX2-YW-BR-14)+2 种基金National Basic Research Program of China(2011CB309704)Special Scientific Research Project for Public Interest (Grant No. GYHY201006021)the National Natural Science Foundation of China (Grant Nos.40890155, 40775051, U0733002)
文摘The tropical Indian Ocean (TIO) is warmer than normal during the summer when or after the El Nio decays. The present study investigates the impact of TIO SST on the South Asian High (SAH) in summer. When the TIO is warmer, the SAH strengthens and its center shifts southward. It is found that the variations in the SAH cannot be accounted for by the precipitation anomaly. A possible mechanism is proposed to explain the connection between the TIO and SAH: warmer SST in the TIO changes the equivalent potential temperature (EPT) in the atmospheric boundary layer (ABL), alters the temperature profile of the moist atmosphere, warms the troposphere, which produces significant positive height anomaly over South Asia and modifies the SAH. An atmospheric general circulation model, ECHAM5, which has a reasonable prediction skill in the TIO and South Asia, was selected to test the effects of TIO SST on the SAH. The experiment with idealized heating over the TIO reproduced the response of the SAH to TIO warming. The results suggest that the TIO-induced EPT change in the ABL can account for the variations in the SAH.
基金This research was jointly sponsored by "The National Key Programme for Developing Basic Sciences"project (1998040900)Part Ⅰ, and the National Natural Science Foundation of China Project:"Studies on Interaction between the South Asia High and the Asian Monsoon and lts Mechanisms"under Grant No.40175021.
文摘A case is reported, during which the Subtropical High over the Western Pacific (hereafter, SHWP in abbreviation) shifted northwestward and met-yu at Chaniiang River valley ended. Several numerical experiments onSHWP activity influenced by the heating over south Asia monsoon area are carried out, and the statistic significance of the results is checked. The results indicate that the enhancement of positive heating over South Asia willmotivate a wave-like series of anomaly centers, which propagate northeastward from the maximum heating center.so that a strong positive potential height anomaly center will set up from North China to Japan at Day X resultingin the enhancement of SHWP. Comparison of the influence upon SHWP by the heating over south Asia monsoonarea with that over ITCZ area south to SHWP is also carried out. It is pointed out that the heating over South Asiamonsoon area tends to favor SHWP north\vard movement while the heating over ITCZ area tends to thvor SHWPwestward stretching. As for the time to begin to influence on SHWP, the heating over south Asia monsoon areafavors the enhancement of SHWP atter Day 3 while that over ITCZ south to SHWP effects atter Day 5.
文摘[Objective] The aim was to study the relation among summer rainfall in south Shandong and high pressure in South Asia and atmospheric circulation.[Method] Taking the precipitation in south Shandong along the Yellow River and Huaihe River,using the NCEP/NCAR data and summer rainfall data in south Shandong in summer from 1961 to 2005,the characteristics of high pressure in South Asia and atmospheric circulation in drought year and flood year in summer in south Shandong Province were expounded.The mechanism of 100 hPa pressure in South Asian influencing precipitation in south Shandong Province was discussed.The interaction of different equipment,different altitude and different system of atmosphere circulation in low and high layer was expounded.[Results] The first mode of EOF decomposition of precipitation in summer in south Shandong Province explained above 63% variances and reflected universal form of precipitation.The difference of central position of the central position of height field of high pressure in South Asia in drought and flood year was small.But the wind field center was inconsistent.As the area of SAH was smaller and its eastern ridge line stretched to the Western Pacific between the middle of south Shandong and Changjiang Estuary,flood summer occurred when there was an unusual cyclone lied in the east of 90° E and south of Lake Baikal.The area of SAH was larger and its eastern ridge line stretching to the Western Pacific over Changjiang Estuary,drought summer occurred,when there was an unusual anticyclone lied in the east of 90° E and south of Lake Baikal.SAH and summer rainfall also had close relationship with Tele-connection Patterns over the Eurasia continent and EAP Tele-connection.When the height anomaly was in "+-+" form in the north of the Caspian Sea,around Lake Baikal and Kamchatka,and when the height anomaly in East Asia-West Pacific area was in "-+" form from low altitude to high altitude,there was much precipitation in summer;and conversely,it was drought in summer in south Shandong.[Conclusion] It provided the oretical basis for summer rainfall in south Shandong.
基金Key Laboratory on Natural Disasters for Jiangsu Province (KLME050210)
文摘Comparisons of the west Pacific subtropical high with the South Asia High are made using the NCEP/NCAR and ECMWF 500 hPa and 100 hPa monthly boreal geopotential height fields for the period 1961-2000. Discrepancies are found for the time prior to 1980. The west Pacific subtropical high in the NCEP/NCAR data is less intense than in ECMWF data before 1980. The range and strength of the west Pacific subtropical high variation described by the NCEP/NCAR data are larger than those depicted by ECMWF data. The same situation appears in the 100-hPa geopotential field. These discoveries suggest that the interdecadal variation of the two systems as shown by the NCEP/NCAR data may not be true. Besides, the South Asia High center in the NCEP/NCAR data is obviously stronger than in the ECMWF data during the periods 1969, 1979-1991 and 1992-1995. Furthermore, the range is larger from 1992 to 1995.
基金Special Projects for Forecaster China Meteorological Administration(CMAYBY2011-017)
文摘By analyzing the change of an index for the characteristics of South Asia High and variations of upper-air troughs in 2002–2005,we studied the impact of South Asia high on the beginning and ending of the Mei-yu(i.e.sustained rain corresponding to the ripening season of plum)in Jiangsu province.Statistic verification is conducted on the relationships between the index and the Mei-yu season in 1991–2005 to examine the impacts of the SAH characteristics index on a rain intensity index of Mei-yu and regional distribution of a characteristics index for different annual patterns of Mei-yu.Historical composite is performed of the 100-hPa circulation field for these patterns using the 100-hPa geopotential height of Northern Hemisphere from 2002 to 2005 and 45-year NCEP reanalysis to study the difference in the circulation for different patterns of Mei-yu.Diagnostic and statistic conclusions,which share much in common,have been obtained as follows.(1)The characteristics preceding to and the advancement/retreat of SAH and the movement of westerly troughs are the factors that influence the onset time of the Mei-yu season;after the Mei-yu onset,the progression/withdrawal of SAH and how farther east it extends are determining how long the Mei-yu lasts and when it ends.(2)During the Mei-yu,the general 100-hPa circulation situation and average characteristics of the SAH are well corresponding to the characteristics of the season and annual patterns of Mei-yu.In addition,the averages of the SAH ridgeline and east-extending index for June,July and the Mei-yu season have some implications to the forecast of the index of Mei-yu intensity.These conclusions can be served as powerful means in determining the starting/ending dates, duration and annual pattern of the Mei-yu season.
基金National Key Fundamental Research Development Program Planning"973"(2009CB4215032013CB430103)+2 种基金Natural Science Foundation of China(41375058)Construction of Advantageous Disciplines for Higher Education in Jiangsu ProvincePriority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘The NCEP 1°×1°reanalysis of June-to-September dataset between 2002 to 2009 is used in this study to conduct statistical analysis of the relationship between the environmental potential vorticity(PV)on 150 hPa located at the south edge of South Asia High(SAH)and TCs making landfall.The results show that 23 of the TCs are affected by the PV on 150 hPa located at the south edge of SAH between 2002 to2009,and three TCs'center pressure decline after the high-value environmental PV moves to the center of the TCs.These three TCs are Senlaku(0216),Bilis(0604)and Linfa(0903).Through diagnostic analysis from the viewpoint of isolines,we determined the relationship between the intensification of these TCs and the PV anomaly at high levels;the isentropic surface is close to the high level’s PV anomaly under the influence of the 150-hPa PV anomaly,leading to the decline of isentropic surfaces on both sides of the PV anomaly.Then the warm core of the middle and high levels of the TC strengthens and PV increases at the middle level,and both of them are beneficial to the reinforcement of the cyclonic vorticity in the low level.As a result,the center pressure of the TC declines.According to Wu’s theory of Slantwise Vorticity Development(SVD),the incline of the isentropic surfaces leads to the development of vertical vorticity,contributing to the vertical motion and the release of the latent heat.Then the warm core of the TC strengthens and the TC strengthens,too.Otherwise,piecewise PV inversion also shows that the high-level PV influences the mid-level more than the low level.
基金National Key Basic Research Development Program Project of China(2012CB417202)Key Project of National Natural Science Foundation(91337215)National Natural Science Foundation of China(41275051)
文摘NCEP/NCAR data are utilized to analyze an extreme flood year(1998) and an extreme dry year(2006) in the Sichuan-Chongqing region(SCR) and the results are as follows. The positive divergence of South Asia High(SAH) is stronger in the flood year; the position of the ridge line of SAH is southward compared with the annual average; Western Pacific Subtropical High(WPSH) extends westward and its ridge line is southward. In the drought year, the positive divergence of SAH is weaker, its ridge line is northward, and the position of WPSH is also northward. As shown in the dynamics, in drought(flood) years, negative(positive) vorticity advection in the upper atmosphere can cause the atmosphere to ascend(descend), and anomalous circulation of SAH displays divergence(convergence), and anomalous circulation of the lower atmosphere shows convergence(divergence). Thermal structure of the atmosphere shows that there is warm(cold) temperature advection in the lower atmosphere, and the vertical distribution of diabetic heating causes SAH's local circulation to display convergence(divergence) and affects vertical motion of the lower atmosphere circulation eventually. To some extent, the two extreme years in the SCR is closely related to the vertical motion of atmosphere circulation and the variation of such vertical motion is caused by differences of interactions between SAH and lower atmosphere circulations.
文摘The characteristics of the South Asia high (SAH) and subtropical westerly jets in the summer of 2010 and their relationship with the changes in rainband in China were analyzed. As shown by the results, the SAH in the upper troposphere extended northward relatively late in June 2010. Correspondingly, the subtropical westerly jets on the north side of the SAH jumped northward comparatively late, thus delaying the formation of a strong divergence field in the upper air over the Yangtze-Huaihe River valley. This was one of the main causes for the late onset of plum rains in the Yangtze-Huaihe River valley. In July, there was a vertical structure consisting of upper-level divergence and low-level convergence near the subtropical westerly jets on the north side of the SAH and in the air stream dispersal area on the northeast side of the eastward-extending SAH, which was the dynamic mechanism bringing about frequent and extremely heavy rainstorms during the plum rain period in this year. The SAH in the upper troposphere affected the subtropical high in the lower stratosphere, and thereby led to changes in the main rainband location in China.
文摘In the context of 1958-1997 NCFP NCAR re-analyses, the South Asia high (SAH) was divided into two components, barotropic and haroclinic, the former based on mass weighed vertical integration and the latter on the difference between the measured circulation and the barotropic component counterpart, whereupon the barotropic and baroclinic circulation conversion features were addressed of the research SAH during its seasonal variation. Evidence suggests that i) in summer (winter). the SAH is a thermal (dynamical) system. with dominant baroclinicity (barotropicity). either of the components accounting for approximately 70% of the total contribution; ii) as time progresses from winter to summer, accompanied by the barotropic SAH evolving into its baroclinic analog, the SAH is moving under the" thermal guidance" of its baroclinic component circulation, suggesting that the component circulation precedes the system itself in variation. iii) the reversal happens when it goes from summer to winter, with the SAH displacement under the" dynamic steering" of its barotropic component circulation.
文摘基于美国国家海洋和大气管理局(National Oceanic and Atmospheric Administration, NOAA)全球范围扩展重建海面温度资料第5版本(Extended Reconstructed Sea Surface Temperature version 5,ERSSTv5),以及美国国家环境预报中心和国家大气研究中心NCEP(National Centers for Environmental Prediction)/NCAR(National Center for Atmospheric Research)逐月全球再分析资料,采用相关、回归、合成及物理量诊断等方法,对2022年夏季中国大范围高温相关环流异常的可能成因进行了分析。结果表明:(1)2022年夏季南亚高压偏强并分别向东、西方向扩展,西太平洋副热带高压(以下简称“副高”)异常偏强西伸。2022夏季为拉尼娜(La Nina)年,但热带大西洋垂直上升环流相对西太平洋更强,且热带印度洋到西太平洋热带垂直上升环流异常也偏强。(2)2022年热带大西洋、印度洋到西太平洋上空垂直环流异常和La Nina共同作用,使得夏季南亚高压和西太平洋副高极端异常。La Nina和印度洋到西太平洋垂直环流异常有利于南亚高压和西太平洋副高的偏强西伸;热带大西洋环流异常则既有利于南亚高压的加强及东扩,也有利于西太平洋副高偏强西伸。(3)印度洋到西太平洋垂直环流主要通过局地经向哈得来(Hadley)环流影响青藏高原到中国东部的环流异常,表现为青藏高原到中国东部中低层为显著的辐散异常;热带大西洋则通过引起纬向风异常(急流异常),激发遥相关波列并向下游传播,进而影响青藏高原到中国东部地区的环流异常。
文摘利用1961—2022年四川155个国家气象站逐日气温、降水资料和NCEP/NCAR再分析资料等,对2022年四川持续高温干旱事件特征及成因进行分析。结果表明:2022年夏季四川出现极端高温干旱天气,全省平均气温、最高气温、高温日数均突破历史同期极值,73.0%的站点出现重旱及以上旱情,为1961年以来最严重高温伏旱天气气候事件。南亚高压北跳东进,异常偏强偏北,500 h Pa青藏高压发展东移,或西太平洋副热带高压加强西伸北抬,与南亚高压叠加,形成稳定正压结构控制四川,是造成高温干旱的主要原因。亚洲中纬度地区盛行纬向环流,伊朗高压、青藏高压和西太平洋副热带高压打通形成高压带,盛行下沉辐散气流,阻挡中高纬冷空气南下和低纬暖湿气流北上,导致四川地区降水异常偏少,是高温干旱的间接原因。
