The Hadley Circulation(HC),a fundamental component of global atmospheric circulation,plays an important role in the global energy balance and transport of moisture.The interaction between ENSO and the HC significantly...The Hadley Circulation(HC),a fundamental component of global atmospheric circulation,plays an important role in the global energy balance and transport of moisture.The interaction between ENSO and the HC significantly impacts tropical climate and has broad implications for global climate variability through atmospheric teleconnections.The HC is usually represented by the mass stream function.As a result,it can rarely be observed through in-situ measurement.Reanalysis datasets and CMIP models are frequently used to investigate the properties of the HC.Previous studies systematically assess the capability of these CMIP models to represent the spatial distribution and intensity of the HC anomalies associated with ENSO events.However,most of these studies investigate the HC anomaly from a global perspective.In this work,we focus on evaluating the ability of CMIP6 models to capture the three-dimensional features of ENSO-related HC anomalies in comparison to that in six reanalysis datasets.Results show a consistent westward shift of the ENSO-related HC over the tropical Central-Eastern Pacific in almost all CMIP6 models,accompanied by a weakening of the asymmetric component of the ENSO-related HC over the equatorial Pacific.The former is mainly attributed to the westward extension of the Pacific cold tongue in CMIP models,while the latter is more related to the southward shift of the ENSO-related SST and precipitation anomalies in CMIP models.One should be aware of these biases when studying the ENSO-related atmospheric circulation changes.Our study has broad implications for ENSO simulations and the predictability of ENSO-related global climate variabilities.展开更多
The discrepancy in the trends of the global zonal mean(GZM)intensity of the Hadley circulation(HCI)between reanalysis data and model simulations has been a problem for understanding the changes in HCI and the influenc...The discrepancy in the trends of the global zonal mean(GZM)intensity of the Hadley circulation(HCI)between reanalysis data and model simulations has been a problem for understanding the changes in HCI and the influence of external forcings.To understand the reason for this discrepancy,this study investigates the trends of intensity of regional HCI of the Northern Hemisphere over the eastern Pacific(EPA),western Pacific(WPA),Atlantic(ATL),Africa(AFR),the Indian Ocean(IDO),and residual area(RA),based on six reanalysis datasets and 13 CMIP6 models.In reanalysis data,the trends in regional HCI over EPA and ATL(WPA and AFR)contribute to(partially offset)the increasing trend in GZM HCI,while the trends in regional HCI over IDO are different in different reanalysis data.The CMIP6 models skillfully reproduce the trends in regional HCI over EPA,ATL,WPA,and AFR,but simulate notable decreasing trends in regional HCI over IDO,which is a key reason for the opposite trends in GZM HCI between reanalysis data and models.The discrepancy in IDO can be attributed to differences in the simulation of diabatic heating and zonal friction between reanalysis data and models.Optimal fingerprint analysis indicates that anthropogenic(ANT)and non-greenhouse gas(NOGHG)forcings are the dominant drivers of the HCI trends in the EPA and ATL regions.In the WPA(AFR)region,NOGHG(ANT)forcing serves as the primary driver.The findings contribute to improving the representation of regional HCI trends in models and improving the attribution of external forcings.展开更多
El Nino-Southern Oscillation(ENSO),the leading mode of global interannual variability,usually intensifies the Hadley Circulation(HC),and meanwhile constrains its meridional extension,leading to an equatorward movement...El Nino-Southern Oscillation(ENSO),the leading mode of global interannual variability,usually intensifies the Hadley Circulation(HC),and meanwhile constrains its meridional extension,leading to an equatorward movement of the jet system.Previous studies have investigated the response of HC to ENSO events using different reanalysis datasets and evaluated their capability in capturing the main features of ENSO-associated HC anomalies.However,these studies mainly focused on the global HC,represented by a zonal-mean mass stream function(MSF).Comparatively fewer studies have evaluated HC responses from a regional perspective,partly due to the prerequisite of the Stokes MSF,which prevents us from integrating a regional HC.In this study,we adopt a recently developed technique to construct the three-dimensional structure of HC and evaluate the capability of eight state-of-the-art reanalyses in reproducing the regional HC response to ENSO events.Results show that all eight reanalyses reproduce the spatial structure of HC responses well,with an intensified HC around the central-eastern Pacific but weakened circulations around the Indo-Pacific warm pool and tropical Atlantic.The spatial correlation coefficient of the three-dimensional HC anomalies among the different datasets is always larger than 0.93.However,these datasets may not capture the amplitudes of the HC responses well.This uncertainty is especially large for ENSO-associated equatorially asymmetric HC anomalies,with the maximum amplitude in Climate Forecast System Reanalysis(CFSR)being about 2.7 times the minimum value in the Twentieth Century Reanalysis(20CR).One should be careful when using reanalysis data to evaluate the intensity of ENSO-associated HC anomalies.展开更多
本文分析了1948~2007年北半球夏季Hadley环流的主导模态及其变率,结果表明:北半球夏季Hadley环流变率的主导模态包括两个赤道非对称模态,其主体分别位于北半球(简称为AMN)和南半球(简称AMS)和一个赤道准对称的模态(简称QSM),AMN和AMS主...本文分析了1948~2007年北半球夏季Hadley环流的主导模态及其变率,结果表明:北半球夏季Hadley环流变率的主导模态包括两个赤道非对称模态,其主体分别位于北半球(简称为AMN)和南半球(简称AMS)和一个赤道准对称的模态(简称QSM),AMN和AMS主要表征Hadley环流的年代际变率部分,而QSM主要表征Hadley环流的年际变率部分。AMN的时间系数呈现明显的减弱趋势,AMS的时间系数则表现为明显的增强趋势,两个模态的年代际变率表明:北半球夏季Hadley环流发生了显著的年代际转型,在1970年代以前呈现"北强南弱"型,之后转变为"南强北弱"型。印度洋—西太平洋暖池和热带大西洋赤道带海温的异常增暖以及由热带大西洋和印度洋海温非均匀增暖形成的减弱的北半球大尺度经向海温梯度和加强的南半球大尺度经向海温梯度可能是导致上述Hadley环流变率的重要影响因子。不同于两个非对称模态,QSM模态的变率主要与热带东太平洋的海温以及Ni^no3.4指数有明显的线性关系,说明ENSO对夏季Hadley环流的影响主要是在年际尺度上。对Hadley环流年代际转型的进一步分析发现,其越赤道部分的减弱与东半球热带季风区经向越赤道环流的减弱有密切联系。相关和合成分析的结果显示,南海季风、南亚东区季风以及西非季风的强弱与越赤道环流异常有显著相关,热带季风在这些区域的减弱趋势很可能共同受到北半球夏季Hadley环流年代际转型中越赤道环流减弱的影响。然而,南亚西区季风与经向环流没有明显相关,同时也未呈现显著的年代际趋势,这一结果从环流的角度验证了Li and Zeng(2002)将南亚季风区划分为东区和西区的合理性。展开更多
利用ECMWF最新发布的Interim再分析资料,计算了东亚季风区Hadley环流质量流函数,并使用EOF分解、相关分析及合成分析等统计方法,分析了夏季东亚季风区Hadley环流上升支结构的异常特征及其对我国长江流域降水的影响。发现夏季东亚季风区H...利用ECMWF最新发布的Interim再分析资料,计算了东亚季风区Hadley环流质量流函数,并使用EOF分解、相关分析及合成分析等统计方法,分析了夏季东亚季风区Hadley环流上升支结构的异常特征及其对我国长江流域降水的影响。发现夏季东亚季风区Hadley环流上升支具有独特的双上升中心结构,两上升中心的位置分别对应东亚夏季风系统中的两条辐合带——热带季风槽及梅雨锋。上升支的主要异常模态表现为两个上升中心"跷跷板"型的反相异常。与梅雨锋对应的副热带上升中心强度与长江流域降水呈正相关关系,即当其偏强时,长江流域降水偏多,反之亦然。副热带支偏强时,低层西太平洋副热带高压偏南导致气流在长江流域异常辐合,其异常西南风水汽输送使得长江流域有异常水汽辐合,高层气流在长江流域异常辐散。同时鄂霍次克海附近阻塞活动偏强,东亚沿海地区500 h Pa高度场出现"+-+"的经向异常型。这些异常型均有利于长江流域的降水。展开更多
基金supported by the National Science Fund for Distinguished Young Scholars(Grant No.42325605)the National Natural Science Foundation of China(Grant No.42176243)the National Natural Science Foundation of China(Grant No.42222501)。
文摘The Hadley Circulation(HC),a fundamental component of global atmospheric circulation,plays an important role in the global energy balance and transport of moisture.The interaction between ENSO and the HC significantly impacts tropical climate and has broad implications for global climate variability through atmospheric teleconnections.The HC is usually represented by the mass stream function.As a result,it can rarely be observed through in-situ measurement.Reanalysis datasets and CMIP models are frequently used to investigate the properties of the HC.Previous studies systematically assess the capability of these CMIP models to represent the spatial distribution and intensity of the HC anomalies associated with ENSO events.However,most of these studies investigate the HC anomaly from a global perspective.In this work,we focus on evaluating the ability of CMIP6 models to capture the three-dimensional features of ENSO-related HC anomalies in comparison to that in six reanalysis datasets.Results show a consistent westward shift of the ENSO-related HC over the tropical Central-Eastern Pacific in almost all CMIP6 models,accompanied by a weakening of the asymmetric component of the ENSO-related HC over the equatorial Pacific.The former is mainly attributed to the westward extension of the Pacific cold tongue in CMIP models,while the latter is more related to the southward shift of the ENSO-related SST and precipitation anomalies in CMIP models.One should be aware of these biases when studying the ENSO-related atmospheric circulation changes.Our study has broad implications for ENSO simulations and the predictability of ENSO-related global climate variabilities.
基金the National Key Research and Development Program of China[grant number 2022YFF0801704].
文摘The discrepancy in the trends of the global zonal mean(GZM)intensity of the Hadley circulation(HCI)between reanalysis data and model simulations has been a problem for understanding the changes in HCI and the influence of external forcings.To understand the reason for this discrepancy,this study investigates the trends of intensity of regional HCI of the Northern Hemisphere over the eastern Pacific(EPA),western Pacific(WPA),Atlantic(ATL),Africa(AFR),the Indian Ocean(IDO),and residual area(RA),based on six reanalysis datasets and 13 CMIP6 models.In reanalysis data,the trends in regional HCI over EPA and ATL(WPA and AFR)contribute to(partially offset)the increasing trend in GZM HCI,while the trends in regional HCI over IDO are different in different reanalysis data.The CMIP6 models skillfully reproduce the trends in regional HCI over EPA,ATL,WPA,and AFR,but simulate notable decreasing trends in regional HCI over IDO,which is a key reason for the opposite trends in GZM HCI between reanalysis data and models.The discrepancy in IDO can be attributed to differences in the simulation of diabatic heating and zonal friction between reanalysis data and models.Optimal fingerprint analysis indicates that anthropogenic(ANT)and non-greenhouse gas(NOGHG)forcings are the dominant drivers of the HCI trends in the EPA and ATL regions.In the WPA(AFR)region,NOGHG(ANT)forcing serves as the primary driver.The findings contribute to improving the representation of regional HCI trends in models and improving the attribution of external forcings.
基金supported by the National Key Research and Development Program of China(Grant No.2018YFA0605703)the National Natural Science Foundation of China(Grant Nos.42176243,41976193 and 41676190)supported by National Natural Science Foundation of China(Grant No.41975079)。
文摘El Nino-Southern Oscillation(ENSO),the leading mode of global interannual variability,usually intensifies the Hadley Circulation(HC),and meanwhile constrains its meridional extension,leading to an equatorward movement of the jet system.Previous studies have investigated the response of HC to ENSO events using different reanalysis datasets and evaluated their capability in capturing the main features of ENSO-associated HC anomalies.However,these studies mainly focused on the global HC,represented by a zonal-mean mass stream function(MSF).Comparatively fewer studies have evaluated HC responses from a regional perspective,partly due to the prerequisite of the Stokes MSF,which prevents us from integrating a regional HC.In this study,we adopt a recently developed technique to construct the three-dimensional structure of HC and evaluate the capability of eight state-of-the-art reanalyses in reproducing the regional HC response to ENSO events.Results show that all eight reanalyses reproduce the spatial structure of HC responses well,with an intensified HC around the central-eastern Pacific but weakened circulations around the Indo-Pacific warm pool and tropical Atlantic.The spatial correlation coefficient of the three-dimensional HC anomalies among the different datasets is always larger than 0.93.However,these datasets may not capture the amplitudes of the HC responses well.This uncertainty is especially large for ENSO-associated equatorially asymmetric HC anomalies,with the maximum amplitude in Climate Forecast System Reanalysis(CFSR)being about 2.7 times the minimum value in the Twentieth Century Reanalysis(20CR).One should be careful when using reanalysis data to evaluate the intensity of ENSO-associated HC anomalies.
文摘本文分析了1948~2007年北半球夏季Hadley环流的主导模态及其变率,结果表明:北半球夏季Hadley环流变率的主导模态包括两个赤道非对称模态,其主体分别位于北半球(简称为AMN)和南半球(简称AMS)和一个赤道准对称的模态(简称QSM),AMN和AMS主要表征Hadley环流的年代际变率部分,而QSM主要表征Hadley环流的年际变率部分。AMN的时间系数呈现明显的减弱趋势,AMS的时间系数则表现为明显的增强趋势,两个模态的年代际变率表明:北半球夏季Hadley环流发生了显著的年代际转型,在1970年代以前呈现"北强南弱"型,之后转变为"南强北弱"型。印度洋—西太平洋暖池和热带大西洋赤道带海温的异常增暖以及由热带大西洋和印度洋海温非均匀增暖形成的减弱的北半球大尺度经向海温梯度和加强的南半球大尺度经向海温梯度可能是导致上述Hadley环流变率的重要影响因子。不同于两个非对称模态,QSM模态的变率主要与热带东太平洋的海温以及Ni^no3.4指数有明显的线性关系,说明ENSO对夏季Hadley环流的影响主要是在年际尺度上。对Hadley环流年代际转型的进一步分析发现,其越赤道部分的减弱与东半球热带季风区经向越赤道环流的减弱有密切联系。相关和合成分析的结果显示,南海季风、南亚东区季风以及西非季风的强弱与越赤道环流异常有显著相关,热带季风在这些区域的减弱趋势很可能共同受到北半球夏季Hadley环流年代际转型中越赤道环流减弱的影响。然而,南亚西区季风与经向环流没有明显相关,同时也未呈现显著的年代际趋势,这一结果从环流的角度验证了Li and Zeng(2002)将南亚季风区划分为东区和西区的合理性。
文摘利用ECMWF最新发布的Interim再分析资料,计算了东亚季风区Hadley环流质量流函数,并使用EOF分解、相关分析及合成分析等统计方法,分析了夏季东亚季风区Hadley环流上升支结构的异常特征及其对我国长江流域降水的影响。发现夏季东亚季风区Hadley环流上升支具有独特的双上升中心结构,两上升中心的位置分别对应东亚夏季风系统中的两条辐合带——热带季风槽及梅雨锋。上升支的主要异常模态表现为两个上升中心"跷跷板"型的反相异常。与梅雨锋对应的副热带上升中心强度与长江流域降水呈正相关关系,即当其偏强时,长江流域降水偏多,反之亦然。副热带支偏强时,低层西太平洋副热带高压偏南导致气流在长江流域异常辐合,其异常西南风水汽输送使得长江流域有异常水汽辐合,高层气流在长江流域异常辐散。同时鄂霍次克海附近阻塞活动偏强,东亚沿海地区500 h Pa高度场出现"+-+"的经向异常型。这些异常型均有利于长江流域的降水。
