Climate models are essential for understanding past,present,and future changes in atmospheric circulation,with circulation modes providing key sources of seasonal predictability and prediction uncertainties for both g...Climate models are essential for understanding past,present,and future changes in atmospheric circulation,with circulation modes providing key sources of seasonal predictability and prediction uncertainties for both global and regional climates.This study assesses the performance of models participating in phase 6 of the Coupled Model Intercomparison Project in simulating interannual variability modes of Northern Hemisphere 500-hPa geopotential height during winter and summer,distinguishing predictable(potentially predictable on seasonal or longer timescales)and unpredictable(intraseasonal and essentially unpredictable at long range)components,using reanalysis data and a variance decomposition method.Although most models effectively capture unpredictable modes in reanalysis,their ability to reproduce dominant predictable modes-specifically the Pacific-North American pattern,Arctic Oscillation,and Western Pacific Oscillation in winter,and the East Atlantic and North Atlantic Oscillations in summer-varies notably.An optimal ensemble is identified to distinguish(a)predictable-external modes,dominated by external forcing,and(b)predictable-internal modes,associated with slow internal variability,during the historical period(1950-2014)and the SSP5-8.5 scenario(2036-2100).Under increased radiative forcing,the leading winter/summer predictable-external mode exhibits a more uniform spatial distribution,remarkably larger trend and annual variance,and enhanced height-sea surface temperature(SST)covariance under SSP5-8.5 compared to historical conditions.The dominant winter/summer predictable-internal modes also exhibit increased variance and height-SST covariance under SSP5-8.5,along with localized changes in spatial configuration.Minimal changes are observed in spatial distribution or variance for dominant winter/summer unpredictable modes under SSP5-8.5.This study,from a predictive perspective,deepens our understanding of model uncertainties and projected changes in circulations.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
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
基金supported by the National Natural Science Foundation of China(Grant Nos.U2342210 and 42275043)the National Institute of Natural Hazards,Ministry of Emergency Management of China(Grant Nos.J2223806,ZDJ2024-25 and ZDJ2025-34)。
文摘Climate models are essential for understanding past,present,and future changes in atmospheric circulation,with circulation modes providing key sources of seasonal predictability and prediction uncertainties for both global and regional climates.This study assesses the performance of models participating in phase 6 of the Coupled Model Intercomparison Project in simulating interannual variability modes of Northern Hemisphere 500-hPa geopotential height during winter and summer,distinguishing predictable(potentially predictable on seasonal or longer timescales)and unpredictable(intraseasonal and essentially unpredictable at long range)components,using reanalysis data and a variance decomposition method.Although most models effectively capture unpredictable modes in reanalysis,their ability to reproduce dominant predictable modes-specifically the Pacific-North American pattern,Arctic Oscillation,and Western Pacific Oscillation in winter,and the East Atlantic and North Atlantic Oscillations in summer-varies notably.An optimal ensemble is identified to distinguish(a)predictable-external modes,dominated by external forcing,and(b)predictable-internal modes,associated with slow internal variability,during the historical period(1950-2014)and the SSP5-8.5 scenario(2036-2100).Under increased radiative forcing,the leading winter/summer predictable-external mode exhibits a more uniform spatial distribution,remarkably larger trend and annual variance,and enhanced height-sea surface temperature(SST)covariance under SSP5-8.5 compared to historical conditions.The dominant winter/summer predictable-internal modes also exhibit increased variance and height-SST covariance under SSP5-8.5,along with localized changes in spatial configuration.Minimal changes are observed in spatial distribution or variance for dominant winter/summer unpredictable modes under SSP5-8.5.This study,from a predictive perspective,deepens our understanding of model uncertainties and projected changes in circulations.
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 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.
