海洋热浪是发生在海洋上的极端高温事件,对海洋环境和生态系统具有破坏性影响。文章采用1960—2020年第五代欧洲中期天气预报中心再分析资料(European centre for medium-range weather forecasts reanalysis v5,ERA5)和英国气象局哈德...海洋热浪是发生在海洋上的极端高温事件,对海洋环境和生态系统具有破坏性影响。文章采用1960—2020年第五代欧洲中期天气预报中心再分析资料(European centre for medium-range weather forecasts reanalysis v5,ERA5)和英国气象局哈德来中心全球海冰和海洋表面温度资料集(Hadley centre global sea ie and sea surface temperature,HadISST)以及地球系统模式(community Earth system model,CESM1)北大西洋理想试验数据等,通过相关、合成分析等多种统计方法,研究了厄尔尼诺–南方涛动(El Niño-Southern Oscillation,ENSO)与次年初夏西太平洋海洋热浪年际关系的变化特征,并进一步探讨了二者关系发生年代际变化的可能成因。研究结果表明:1)ENSO与次年初夏西太平洋海洋热浪月数的年际关系具有明显的年代际变化特征,北大西洋多年代际振荡(Atantic multidecadal oscillation,AMO)是二者年际关系发生年代际变化的主要成因。当AMO处于正位相时,ENSO与次年初夏西太平洋海洋热浪存在显著的正相关关系,而当AMO处于负位相时,上述二者相关关系不再显著;2)AMO主要通过调控ENSO事件的强度进而影响西北太平洋大气环流的异常响应,从而进一步影响ENSO与次年初夏西太平洋海洋热浪之间的关系。当AMO处于负(正)位相时,相对较强(弱)的ENSO事件通过强(弱)风–蒸发–海温正反馈过程,使得ENSO事件次年初夏西北太平洋地区产生位置相对偏东(西)、强度相对偏强(弱)的异常反气旋/气旋。异常反气旋/气旋的位置和强度导致初夏西太平洋海洋热浪的分布在AMO正、负位相存在显著差异。展开更多
Winter precipitation over eastern China displays remarkable interannual variability,which has been suggested to be closely related to El Niño-Southern Oscillation(ENSO).This study finds that ENSO impacts on easte...Winter precipitation over eastern China displays remarkable interannual variability,which has been suggested to be closely related to El Niño-Southern Oscillation(ENSO).This study finds that ENSO impacts on eastern China precipitation patterns exhibit obvious differences in early(November-December)and late(January-February)winter.In early winter,precipitation anomalies associated with ENSO are characterized by a monopole spatial distribution over eastern China.In contrast,the precipitation anomaly pattern in late winter remarkably changes,manifesting as a dipole spatial distribution.The noteworthy change in precipitation responses from early to late winter can be largely attributed to the seasonally varying Kuroshio anticyclonic anomalies.During the early winter of El Niño years,anticyclonic circulation anomalies appear both over the Philippine Sea and Kuroshio region,enhancing water vapor transport to the entirety of eastern China,thus contributing to more precipitation there.During the late winter of El Niño years,the anticyclone over the Philippine Sea is further strengthened,while the one over the Kuroshio dissipates,which could result in differing water vapor transport between northern and southern parts of eastern China and thus a dipole precipitation distribution.Roughly the opposite anomalies of circulation and precipitation are displayed during La Niña winters.Further analysis suggests that the seasonally-varying Kuroshio anticyclonic anomalies are possibly related to the enhancement of ENSO-related tropical central-eastern Pacific convection from early to late winter.These results have important implications for the seasonal-tointerannual predictability of winter precipitation over eastern China.展开更多
This study investigates the evolution of an extreme anomalous anticyclone(AA)event over Northeast Asia,which was one of the dominant circulation systems responsible for the catastrophic extreme precipitation event in ...This study investigates the evolution of an extreme anomalous anticyclone(AA)event over Northeast Asia,which was one of the dominant circulation systems responsible for the catastrophic extreme precipitation event in July 2021 in Henan,and further explores the significant impact of this AA on surface temperatures beneath it.The results indicate that this AA event over Northeast Asia was unprecedented in terms of intensity and duration.The AA was very persistent and extremely strong for 10 consecutive days from 13 to 22 July 2021.This long-lived and unprecedented AA led to the persistence of warmer surface temperatures beyond the temporal span of the pronounced 500-hPa anticyclonic signature as the surface air temperatures over land in Northeast Asia remained extremely warm through 29 July 2021.Moreover,the sea surface temperatures in the Sea of Japan/East Sea were extremely high for 30 consecutive days from 13 July to 11 August 2021,persisting well after the weakening or departure of this AA.These results emphasize the extreme nature of this AA over Northeast Asia in July 2021 and its role in multiple extreme climate events,even over remote regions.Furthermore,possible reasons for this long-lasting AA are explored,and it is suggested to be a byproduct of a teleconnection pattern over extratropical Eurasia during the first half of its life cycle,and of the Pacific-Japan teleconnection pattern during the latter half.展开更多
Cold surges(CSs)often occur in the mid-latitude regions of the Northern Hemisphere and have enormous effects on socioeconomic development.We report that the occurrences of CSs and persistent CSs(PCSs)have rebounded si...Cold surges(CSs)often occur in the mid-latitude regions of the Northern Hemisphere and have enormous effects on socioeconomic development.We report that the occurrences of CSs and persistent CSs(PCSs)have rebounded since the 1990s,but the trends related to the frequencies of strong CSs(SCSs)and extreme CSs(ECSs)changed from increasing to decreasing after 2000.The highest-ranked model ensemble approach was used to project the occurrences of various CSs under the SSP1-2.6,SSP2-4.5,and SSP5-8.5 scenarios.The frequencies of the total CSs show overall decreasing trends.However,under the SSP1-2.6 scenario,slight increasing trends are noted for SCSs and ECSs in China.Atmospheric circulations that are characterized by an anomalous anticyclonic circulation with a significantly positive 500-hPa geopotential height(Z500)anomaly at high latitudes along with significant negative anomalies in China were favorable for cold air intrusions into China.In addition,the frequencies of all CS types under the SPP5-8.5 scenario greatly decreased in the long term(2071-2100),a finding which is thought to be related to negative SST anomalies in the central and western North Pacific,differences in sea level pressure(SLP)between high-and mid-latitude regions,and a weaker East Asian trough.In terms of ECSs,the decreasing trends observed during the historical period were maintained until 2024 under the SSP1-2.6 scenario.Compared to the SSP1-2.6 scenario,the Z500 pattern showed a trend of strengthened ridges over the Ural region and northern East Asia and weakened troughs over Siberia(60°-90°E)under the SSP2-4.5 and SSP5-8.5 scenarios,contributing to the shift to increasing trends of ECSs after 2014.展开更多
This study investigates the relationship between circulation patterns and austral summer temperature anomalies in southern Africa. The results show that the formation of continental lows tends to increase the thicknes...This study investigates the relationship between circulation patterns and austral summer temperature anomalies in southern Africa. The results show that the formation of continental lows tends to increase the thickness of the lower atmosphere. Further, the distinct variabilities of high and low pressure under the circulation types, influence air mass advection from the adjacent oceans, as well as atmospheric stability over land. Stronger anticyclonic circulation at the western branch of the Mascarene high-pressure system enhances the low-level cold air advection by southeast winds,decreases the thickness, and lowers the temperature over a majority of the land in southern Africa. Conversely, a weaker Mascarene High, coupled with enhanced cyclonic activity in the southwest Indian Ocean increases low-level warm air advection and increases temperature anomalies over vast regions in southern Africa. The ridging of a closed South Atlantic anticyclone at the southern coast of southern Africa results in colder temperatures near the tip of southern Africa due to enhanced low-level cold air advection by southeast winds. However, when the ridge is weak and westerly winds dominate the southern coast of southern Africa, these areas experience temperature increases. The northward track of the Southern Hemisphere mid-latitude cyclone, which can be linked to the negative Southern Annular Mode, reduces the temperature in the southwestern part of southern Africa. Also, during the analysis period, El Ni?o was associated with temperature increases over the central parts of southern Africa;while the positive Indian Ocean dipole was linked to a temperature increase over the northeastern, northwestern, and southwestern parts of southern Africa.展开更多
本文将1980-2021年江南5月降水作为研究对象,采用美国国家气候预测中心(Climate Prediction Center,CPC)降水、美国环境预测中心(National Center for Environmental Prediction,NCEP)大气环流以及英国气象局哈德莱中心(Met Office Hadl...本文将1980-2021年江南5月降水作为研究对象,采用美国国家气候预测中心(Climate Prediction Center,CPC)降水、美国环境预测中心(National Center for Environmental Prediction,NCEP)大气环流以及英国气象局哈德莱中心(Met Office Hadley Centre)海表面温度等资料,对江南5月降水年际变化特征及其与热带印度洋、太平洋的海表面温度异常(Sea surface temperature anomaly,SSTA)以及对流异常的可能联系进行了分析。结果表明,偏涝年通常伴随有自年前秋季开始发展的热带印度洋暖SSTA,5月同期对流层850 hPa在热带东印度洋至中国南海一带出现东风异常,同时热带印度洋上空对流活动旺盛,通过Hadley环流增强了在西北太平洋的下沉气流,共同增强了西北太平洋异常反气旋(Northwest Pacific anomaly anticyclone,WNPAC),促进了水汽向江南地区输送。热带印度洋中东部的冷SSTA自偏旱年前的冬季开始不断发展,在5月同期的热带印度洋异常冷洋面上空表现为对流抑制,与偏涝年相反的异常Hadley环流促使副高减弱东退,撤出南海,不利于水汽向江南地区输送。除热带印度洋外,热带太平洋和海洋性大陆地区的SSTA及其上空的对流活动异常与WNPAC和江南5月降水异常在一些年份也存在一定的关系,但较热带印度洋复杂。展开更多
The studies in China on the formation of the summertime subtropical anticyclone on the climate timescale are reviewed. New insights in resent studies are introduced. It is stressed that either in the free atmosphere o...The studies in China on the formation of the summertime subtropical anticyclone on the climate timescale are reviewed. New insights in resent studies are introduced. It is stressed that either in the free atmosphere or in the planetary boundary, the descending arm of the Hadley cell cannot be considered as a mechanism for the formation of the subtropical anticyclone. Then the theories of thermal adaptation of the atmosphere to external thermal forcing and the potential vorticity forcing are developed to understand the formation of the subtropical anticyclone in the three-dimensional domain. Numerical experiments are designed to verify these theories. Results show that in the boreal summer, the formation of the strong South Asian High in the upper troposphere and the subtropical anticyclone over the western Pacific in the middle and lower troposphere is, to a great extent, due to the convective latent heating associated with the Asian monsoon, but affected by orography and the surface sensible heating over the continents. On the other hand, the formation of the subtropical anticyclone at the surface over the northern Pacific and in the upper troposphere over North America is mainly due to the strong surface sensible heating over North America, but affected by radiation cooling over the eastern North Pacific. Moreover, in the real atmosphere such individual thermal forcing is well organized. By considering the different diabatic heating in synthesis, a quadruple heating pattern is found over each subtropical continent and its adjacent oceans in summer. A distinct circulation pattern accompanies this heating pattern. The global summer subtropical heating and circulation may be viewed as 'mosaics' of such quadruplet heating and circulation patterns respectively. At last, some important issues for further research in understanding and predicting the variations of the subtropical anticyclone are raised.展开更多
The Asian summer monsoon （ASM） anticyclone is a dominant feature of the circulation in the upper troposphere- lower stratosphere （UTLS） during boreal summer, which is found to have persistent maxima in carbon mono...The Asian summer monsoon （ASM） anticyclone is a dominant feature of the circulation in the upper troposphere- lower stratosphere （UTLS） during boreal summer, which is found to have persistent maxima in carbon monoxide （CO）. This enhancement is due to the upward transport of air with high CO from the planetary boundary layer （PBL）, and confinement within the anticyclonic circulation. With rapid urbanization and industrialization, CO surface emissions are relatively high in the ASM region, especially in India and East China. To reveal the transport pathway of CO surface emissions over these two regions, and investigate the contribution of these to the CO distribution within the ASM anticyclone, a source sensitivity experiment was performed using the Weather Research and Forecasting （WRF） with chemistry model （WRF- Chem）. According to the experiment results, the CO within the ASM anticyclone mostly comes from India, while the contribution from East China is insignificant. The result is mainly caused by the different transportation mechanisms. In India, CO transportation is primarily affected by convection. The surface air with high CO over India is directly transported to the upper troposphere, and then confined within the ASM anticyclone, leading to a maximum value in the UTLS region. The CO transportation over East China is affected by deep convection and large-scale circulation, resulting mainly in transportation to Korea, Japan, and the North Pacific Ocean, with little upward transport to the anticyclone, leading to a high CO value at 215 hPa over these regions.展开更多
By employing the NCEP/NCAR reanalysis data sets(1 000 to 10 hPa,2.5°× 2.5°),the thermal forcing impacts are analyzed of an easterly vortex(shortened as EV) over the tropical upper troposphere on the qua...By employing the NCEP/NCAR reanalysis data sets(1 000 to 10 hPa,2.5°× 2.5°),the thermal forcing impacts are analyzed of an easterly vortex(shortened as EV) over the tropical upper troposphere on the quasi-horizontal movement of the Western Pacific Subtropical Anticyclone(shortened as WPS A) during 22-25 June 2003.The relevant mechanisms are discussed as well.It is shown that the distribution and intensity of the non-adiabatic effect near the EV result in the anomalous eastward retreat of the WPSA.The WPSA prefers extending to the colder region,i.e.,it moves toward the region in which the non-adiabatic heating is weakening or the cooling is strengthening.During the WPSA retreat,the apparent changes of non-adiabatic heating illustrate the characteristics of enhanced cooling in the east side of the EV.Meanwhile,the cooling in the west side exhibits a weakened eastward trend,most prominently at 300 hPa in the troposphere.The evidence on the factors causing the change in thermal condition is found:the most important contribution to the heating-rate trend is the vertical transport term,followed in turn by the local change in the heating rate term and the horizontal advection term.As a result,the atmospheric non-adiabatic heating generated by the vertical transport and local change discussed above is mainly connected to the retreat of the WPSA.展开更多
The simulation characteristics of the seasonal evolution of subtropical anticyclones in the Northern Hemisphere are documented for the Flexible Global Ocean-Atmosphere-Land System model, Spectral Version 2 （FGOALS-s2...The simulation characteristics of the seasonal evolution of subtropical anticyclones in the Northern Hemisphere are documented for the Flexible Global Ocean-Atmosphere-Land System model, Spectral Version 2 （FGOALS-s2）, developed at the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, the Institute of Atmospheric Physics. An understanding of the seasonal evolution of the subtropical anticyclones is also addressed. Compared with the global analysis established by the European Centre for Medium-Range Forecasts, the ERA-40 global reanalysis data, the general features of subtropical anticyclones and their evolution are simulated well in both winter and summer, while in spring a pronounced bias in the generation of the South Asia Anticyclone（SAA） exists. Its main deviation in geopotential height from the reanalysis is consistent with the bias of temperature in the troposphere. It is found that condensation heating （CO） plays a dominant role in the seasonal development of the SAA and the subtropical anticyclone over the western Pacific （SAWP） in the middle troposphere. The CO biases in the model account for the biases in the establishment of the SAA in spring and the weaker strength of the SAA and the SAWP from spring to summer. CO is persistently overestimated in the central-east tropical Pacific from winter to summer, while it is underestimated over the area from the South China Sea to the western Pacific from spring to summer. Such biases generate an illusive anticyclonic gyre in the upper troposphere above the middle Pacific and delay the generation of the SAA over South Asia in April. In mid- summer, the simulated SAA is located farther north than in the ERA-40 data owing to excessively strong surface sensible heating （SE） to the north of the Tibetan Plateau. Whereas, the two surface subtropical anticyclones in the eastern oceans during spring to summer are controlled mainly by the surface SE over the two continents in the Northern Hemisphere, which are simulated reasonably well, albeit with their centers shifted westwards owing to the weaker longwave radiation cooling in the simulation associated with much weaker local stratiform cloud. Further improvements in the related parameterization of physical processes are therefore identified.展开更多
Based on the actual circulation structure as well as weather characters over East_Asia subtropical region in summer, by using three_dimension non_linear forced/dissipated dynamic model, the activities of subtropical a...Based on the actual circulation structure as well as weather characters over East_Asia subtropical region in summer, by using three_dimension non_linear forced/dissipated dynamic model, the activities of subtropical anticyclone over East_Asia have been studied and discussed. The potential enstrophy criteria of system stability have been derived and also been analysed. The criterion can provide useful reference for analysing and predicting subtropical anticyclone's extending/shrinking as well as corresponding weather over East_Asia in summer.展开更多
文摘海洋热浪是发生在海洋上的极端高温事件,对海洋环境和生态系统具有破坏性影响。文章采用1960—2020年第五代欧洲中期天气预报中心再分析资料(European centre for medium-range weather forecasts reanalysis v5,ERA5)和英国气象局哈德来中心全球海冰和海洋表面温度资料集(Hadley centre global sea ie and sea surface temperature,HadISST)以及地球系统模式(community Earth system model,CESM1)北大西洋理想试验数据等,通过相关、合成分析等多种统计方法,研究了厄尔尼诺–南方涛动(El Niño-Southern Oscillation,ENSO)与次年初夏西太平洋海洋热浪年际关系的变化特征,并进一步探讨了二者关系发生年代际变化的可能成因。研究结果表明:1)ENSO与次年初夏西太平洋海洋热浪月数的年际关系具有明显的年代际变化特征,北大西洋多年代际振荡(Atantic multidecadal oscillation,AMO)是二者年际关系发生年代际变化的主要成因。当AMO处于正位相时,ENSO与次年初夏西太平洋海洋热浪存在显著的正相关关系,而当AMO处于负位相时,上述二者相关关系不再显著;2)AMO主要通过调控ENSO事件的强度进而影响西北太平洋大气环流的异常响应,从而进一步影响ENSO与次年初夏西太平洋海洋热浪之间的关系。当AMO处于负(正)位相时,相对较强(弱)的ENSO事件通过强(弱)风–蒸发–海温正反馈过程,使得ENSO事件次年初夏西北太平洋地区产生位置相对偏东(西)、强度相对偏强(弱)的异常反气旋/气旋。异常反气旋/气旋的位置和强度导致初夏西太平洋海洋热浪的分布在AMO正、负位相存在显著差异。
文摘2024年春季(3—5月)我国平均降水量为163 mm,为1961年以来历史同期第六多,4—5月东部地区旱涝灾害并重,华南和江南大部降水较常年同期偏多,尤其是华南大部降水偏多5成以上,多次暴雨过程造成部分地区发生洪涝;而黄淮、江淮北部降水显著偏少,春季后期干旱迅速发展。春季“华南涝、黄淮旱”的形成与东亚大气环流关键系统异常及其季节内阶段性变化密切相关。4月异常偏强、偏南的西北太平洋副热带高压和低层850 hPa偏强的西北太平洋反气旋为华南和江南提供了有利的水汽输送条件,导致南方地区发生多次强降水过程;而黄淮干旱主要受4—5月持续偏强的朝鲜半岛-日本海高压(小笠原高压)和偏南的西北太平洋副热带高压共同影响。此外,春季El Ni o衰减和热带印度洋海温异常偏暖有助于激发异常偏强的西北太平洋反气旋,是我国南方强降水发生的重要海洋外强迫背景。
基金supported by the National Key R&D Program of China (2022YFF0801602)the High-Performance Computing Center of Nanjing University of Information Science and Technology for their support of this work
文摘Winter precipitation over eastern China displays remarkable interannual variability,which has been suggested to be closely related to El Niño-Southern Oscillation(ENSO).This study finds that ENSO impacts on eastern China precipitation patterns exhibit obvious differences in early(November-December)and late(January-February)winter.In early winter,precipitation anomalies associated with ENSO are characterized by a monopole spatial distribution over eastern China.In contrast,the precipitation anomaly pattern in late winter remarkably changes,manifesting as a dipole spatial distribution.The noteworthy change in precipitation responses from early to late winter can be largely attributed to the seasonally varying Kuroshio anticyclonic anomalies.During the early winter of El Niño years,anticyclonic circulation anomalies appear both over the Philippine Sea and Kuroshio region,enhancing water vapor transport to the entirety of eastern China,thus contributing to more precipitation there.During the late winter of El Niño years,the anticyclone over the Philippine Sea is further strengthened,while the one over the Kuroshio dissipates,which could result in differing water vapor transport between northern and southern parts of eastern China and thus a dipole precipitation distribution.Roughly the opposite anomalies of circulation and precipitation are displayed during La Niña winters.Further analysis suggests that the seasonally-varying Kuroshio anticyclonic anomalies are possibly related to the enhancement of ENSO-related tropical central-eastern Pacific convection from early to late winter.These results have important implications for the seasonal-tointerannual predictability of winter precipitation over eastern China.
基金the National Natural Science Foundation of China(Grant Nos.42005029 and 42130504)the Research Program on Decision Services of China Meteorological Administration(Nos.JCZX2023026 and JCZX2022021).
文摘This study investigates the evolution of an extreme anomalous anticyclone(AA)event over Northeast Asia,which was one of the dominant circulation systems responsible for the catastrophic extreme precipitation event in July 2021 in Henan,and further explores the significant impact of this AA on surface temperatures beneath it.The results indicate that this AA event over Northeast Asia was unprecedented in terms of intensity and duration.The AA was very persistent and extremely strong for 10 consecutive days from 13 to 22 July 2021.This long-lived and unprecedented AA led to the persistence of warmer surface temperatures beyond the temporal span of the pronounced 500-hPa anticyclonic signature as the surface air temperatures over land in Northeast Asia remained extremely warm through 29 July 2021.Moreover,the sea surface temperatures in the Sea of Japan/East Sea were extremely high for 30 consecutive days from 13 July to 11 August 2021,persisting well after the weakening or departure of this AA.These results emphasize the extreme nature of this AA over Northeast Asia in July 2021 and its role in multiple extreme climate events,even over remote regions.Furthermore,possible reasons for this long-lasting AA are explored,and it is suggested to be a byproduct of a teleconnection pattern over extratropical Eurasia during the first half of its life cycle,and of the Pacific-Japan teleconnection pattern during the latter half.
基金supported by the National Key R&D Program of China(Grant No.2022YFF0801703)the State Key Laboratory of Earth Surface Processes and Resource Ecology(Grant No.2022-GS-01)in China.
文摘Cold surges(CSs)often occur in the mid-latitude regions of the Northern Hemisphere and have enormous effects on socioeconomic development.We report that the occurrences of CSs and persistent CSs(PCSs)have rebounded since the 1990s,but the trends related to the frequencies of strong CSs(SCSs)and extreme CSs(ECSs)changed from increasing to decreasing after 2000.The highest-ranked model ensemble approach was used to project the occurrences of various CSs under the SSP1-2.6,SSP2-4.5,and SSP5-8.5 scenarios.The frequencies of the total CSs show overall decreasing trends.However,under the SSP1-2.6 scenario,slight increasing trends are noted for SCSs and ECSs in China.Atmospheric circulations that are characterized by an anomalous anticyclonic circulation with a significantly positive 500-hPa geopotential height(Z500)anomaly at high latitudes along with significant negative anomalies in China were favorable for cold air intrusions into China.In addition,the frequencies of all CS types under the SPP5-8.5 scenario greatly decreased in the long term(2071-2100),a finding which is thought to be related to negative SST anomalies in the central and western North Pacific,differences in sea level pressure(SLP)between high-and mid-latitude regions,and a weaker East Asian trough.In terms of ECSs,the decreasing trends observed during the historical period were maintained until 2024 under the SSP1-2.6 scenario.Compared to the SSP1-2.6 scenario,the Z500 pattern showed a trend of strengthened ridges over the Ural region and northern East Asia and weakened troughs over Siberia(60°-90°E)under the SSP2-4.5 and SSP5-8.5 scenarios,contributing to the shift to increasing trends of ECSs after 2014.
文摘This study investigates the relationship between circulation patterns and austral summer temperature anomalies in southern Africa. The results show that the formation of continental lows tends to increase the thickness of the lower atmosphere. Further, the distinct variabilities of high and low pressure under the circulation types, influence air mass advection from the adjacent oceans, as well as atmospheric stability over land. Stronger anticyclonic circulation at the western branch of the Mascarene high-pressure system enhances the low-level cold air advection by southeast winds,decreases the thickness, and lowers the temperature over a majority of the land in southern Africa. Conversely, a weaker Mascarene High, coupled with enhanced cyclonic activity in the southwest Indian Ocean increases low-level warm air advection and increases temperature anomalies over vast regions in southern Africa. The ridging of a closed South Atlantic anticyclone at the southern coast of southern Africa results in colder temperatures near the tip of southern Africa due to enhanced low-level cold air advection by southeast winds. However, when the ridge is weak and westerly winds dominate the southern coast of southern Africa, these areas experience temperature increases. The northward track of the Southern Hemisphere mid-latitude cyclone, which can be linked to the negative Southern Annular Mode, reduces the temperature in the southwestern part of southern Africa. Also, during the analysis period, El Ni?o was associated with temperature increases over the central parts of southern Africa;while the positive Indian Ocean dipole was linked to a temperature increase over the northeastern, northwestern, and southwestern parts of southern Africa.
基金supported by the Chinese Academy of Sciences(Grant No.ZKCX2 SW-210)the National Natural Science Foundation of China(Grant Nos.40135020,40221503,and 40023001).
文摘The studies in China on the formation of the summertime subtropical anticyclone on the climate timescale are reviewed. New insights in resent studies are introduced. It is stressed that either in the free atmosphere or in the planetary boundary, the descending arm of the Hadley cell cannot be considered as a mechanism for the formation of the subtropical anticyclone. Then the theories of thermal adaptation of the atmosphere to external thermal forcing and the potential vorticity forcing are developed to understand the formation of the subtropical anticyclone in the three-dimensional domain. Numerical experiments are designed to verify these theories. Results show that in the boreal summer, the formation of the strong South Asian High in the upper troposphere and the subtropical anticyclone over the western Pacific in the middle and lower troposphere is, to a great extent, due to the convective latent heating associated with the Asian monsoon, but affected by orography and the surface sensible heating over the continents. On the other hand, the formation of the subtropical anticyclone at the surface over the northern Pacific and in the upper troposphere over North America is mainly due to the strong surface sensible heating over North America, but affected by radiation cooling over the eastern North Pacific. Moreover, in the real atmosphere such individual thermal forcing is well organized. By considering the different diabatic heating in synthesis, a quadruple heating pattern is found over each subtropical continent and its adjacent oceans in summer. A distinct circulation pattern accompanies this heating pattern. The global summer subtropical heating and circulation may be viewed as 'mosaics' of such quadruplet heating and circulation patterns respectively. At last, some important issues for further research in understanding and predicting the variations of the subtropical anticyclone are raised.
基金supported by the National Basic Research Program of China (Grant No. 2010CB428602)the National Natural Science Foundation of China (Grant Nos. 41175040 and 91337214)
文摘The Asian summer monsoon （ASM） anticyclone is a dominant feature of the circulation in the upper troposphere- lower stratosphere （UTLS） during boreal summer, which is found to have persistent maxima in carbon monoxide （CO）. This enhancement is due to the upward transport of air with high CO from the planetary boundary layer （PBL）, and confinement within the anticyclonic circulation. With rapid urbanization and industrialization, CO surface emissions are relatively high in the ASM region, especially in India and East China. To reveal the transport pathway of CO surface emissions over these two regions, and investigate the contribution of these to the CO distribution within the ASM anticyclone, a source sensitivity experiment was performed using the Weather Research and Forecasting （WRF） with chemistry model （WRF- Chem）. According to the experiment results, the CO within the ASM anticyclone mostly comes from India, while the contribution from East China is insignificant. The result is mainly caused by the different transportation mechanisms. In India, CO transportation is primarily affected by convection. The surface air with high CO over India is directly transported to the upper troposphere, and then confined within the ASM anticyclone, leading to a maximum value in the UTLS region. The CO transportation over East China is affected by deep convection and large-scale circulation, resulting mainly in transportation to Korea, Japan, and the North Pacific Ocean, with little upward transport to the anticyclone, leading to a high CO value at 215 hPa over these regions.
基金LASW State Key Laboratory Special Fund(2014LASW-A03)National Science Foundation of China(41475041)
文摘By employing the NCEP/NCAR reanalysis data sets(1 000 to 10 hPa,2.5°× 2.5°),the thermal forcing impacts are analyzed of an easterly vortex(shortened as EV) over the tropical upper troposphere on the quasi-horizontal movement of the Western Pacific Subtropical Anticyclone(shortened as WPS A) during 22-25 June 2003.The relevant mechanisms are discussed as well.It is shown that the distribution and intensity of the non-adiabatic effect near the EV result in the anomalous eastward retreat of the WPSA.The WPSA prefers extending to the colder region,i.e.,it moves toward the region in which the non-adiabatic heating is weakening or the cooling is strengthening.During the WPSA retreat,the apparent changes of non-adiabatic heating illustrate the characteristics of enhanced cooling in the east side of the EV.Meanwhile,the cooling in the west side exhibits a weakened eastward trend,most prominently at 300 hPa in the troposphere.The evidence on the factors causing the change in thermal condition is found:the most important contribution to the heating-rate trend is the vertical transport term,followed in turn by the local change in the heating rate term and the horizontal advection term.As a result,the atmospheric non-adiabatic heating generated by the vertical transport and local change discussed above is mainly connected to the retreat of the WPSA.
基金supported by the National Natural Science Foundation of China(Grant No.40925015)the CAS Strategic Priority Research Program(Grant No.XDA01020303)the National Program on Key Basic Research Project(Grant No.2010CB950400)
文摘The simulation characteristics of the seasonal evolution of subtropical anticyclones in the Northern Hemisphere are documented for the Flexible Global Ocean-Atmosphere-Land System model, Spectral Version 2 （FGOALS-s2）, developed at the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, the Institute of Atmospheric Physics. An understanding of the seasonal evolution of the subtropical anticyclones is also addressed. Compared with the global analysis established by the European Centre for Medium-Range Forecasts, the ERA-40 global reanalysis data, the general features of subtropical anticyclones and their evolution are simulated well in both winter and summer, while in spring a pronounced bias in the generation of the South Asia Anticyclone（SAA） exists. Its main deviation in geopotential height from the reanalysis is consistent with the bias of temperature in the troposphere. It is found that condensation heating （CO） plays a dominant role in the seasonal development of the SAA and the subtropical anticyclone over the western Pacific （SAWP） in the middle troposphere. The CO biases in the model account for the biases in the establishment of the SAA in spring and the weaker strength of the SAA and the SAWP from spring to summer. CO is persistently overestimated in the central-east tropical Pacific from winter to summer, while it is underestimated over the area from the South China Sea to the western Pacific from spring to summer. Such biases generate an illusive anticyclonic gyre in the upper troposphere above the middle Pacific and delay the generation of the SAA over South Asia in April. In mid- summer, the simulated SAA is located farther north than in the ERA-40 data owing to excessively strong surface sensible heating （SE） to the north of the Tibetan Plateau. Whereas, the two surface subtropical anticyclones in the eastern oceans during spring to summer are controlled mainly by the surface SE over the two continents in the Northern Hemisphere, which are simulated reasonably well, albeit with their centers shifted westwards owing to the weaker longwave radiation cooling in the simulation associated with much weaker local stratiform cloud. Further improvements in the related parameterization of physical processes are therefore identified.
文摘Based on the actual circulation structure as well as weather characters over East_Asia subtropical region in summer, by using three_dimension non_linear forced/dissipated dynamic model, the activities of subtropical anticyclone over East_Asia have been studied and discussed. The potential enstrophy criteria of system stability have been derived and also been analysed. The criterion can provide useful reference for analysing and predicting subtropical anticyclone's extending/shrinking as well as corresponding weather over East_Asia in summer.
