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
冬季,长持续时间的阻塞高压往往造成更大强度的冷空气堆积,从而导致大范围强寒潮事件的发生,研究阻塞高压的建立和长时间维持机理具有重要的科学意义。本文基于欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecast...冬季,长持续时间的阻塞高压往往造成更大强度的冷空气堆积,从而导致大范围强寒潮事件的发生,研究阻塞高压的建立和长时间维持机理具有重要的科学意义。本文基于欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)提供的1979/1980至2019/2020年ERA5逐日再分析数据,从近41年冬季114次乌拉尔山阻塞高压(以下简称乌山阻高)事件中筛选出6次超长阻高事件(生命期≥10天),对比超长阻高事件与其他阻高事件的异同点,着重探究超长阻高事件发展和维持过程中不同次季节尺度的热、动量输送特征。结果表明:(1)乌山地区位势高度具有显著季节内振荡特征,超长阻高事件的建立和维持均以位势高度异常的季节内尺度分量(20~80天)为主,其他阻高事件的建立和维持则分别取决于位势高度异常的准双周尺度分量(10~20天)和季节内尺度分量。(2)在超长阻高事件发展阶段,定常热量通量梯度的准双周尺度分量和季节内尺度分量均有利于位势高度增加,并且准双周尺度热量输送贡献更大,而在阻高维持阶段贡献最大的是季节内尺度热量输送。相较而言,其他阻高事件中仅季节内尺度分量的热量输送有利于其建立,数值逐渐减小,不利于其维持。(3)动量输送对阻高事件的影响同样不可忽视。阻高事件的发展是准双周尺度和季节内尺度动量输送共同作用的结果,不同的是超长阻高事件中准双周尺度动量输送集中在发展阶段前期,季节内尺度动量输送贯穿整个发展阶段,而其他阻高事件中动量输送相对较小。维持阶段超长阻高事件以定常动量通量的季节内尺度分量为主,其他阻高事件则以定常动量通量的准双周尺度分量为主。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.
文摘冬季,长持续时间的阻塞高压往往造成更大强度的冷空气堆积,从而导致大范围强寒潮事件的发生,研究阻塞高压的建立和长时间维持机理具有重要的科学意义。本文基于欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)提供的1979/1980至2019/2020年ERA5逐日再分析数据,从近41年冬季114次乌拉尔山阻塞高压(以下简称乌山阻高)事件中筛选出6次超长阻高事件(生命期≥10天),对比超长阻高事件与其他阻高事件的异同点,着重探究超长阻高事件发展和维持过程中不同次季节尺度的热、动量输送特征。结果表明:(1)乌山地区位势高度具有显著季节内振荡特征,超长阻高事件的建立和维持均以位势高度异常的季节内尺度分量(20~80天)为主,其他阻高事件的建立和维持则分别取决于位势高度异常的准双周尺度分量(10~20天)和季节内尺度分量。(2)在超长阻高事件发展阶段,定常热量通量梯度的准双周尺度分量和季节内尺度分量均有利于位势高度增加,并且准双周尺度热量输送贡献更大,而在阻高维持阶段贡献最大的是季节内尺度热量输送。相较而言,其他阻高事件中仅季节内尺度分量的热量输送有利于其建立,数值逐渐减小,不利于其维持。(3)动量输送对阻高事件的影响同样不可忽视。阻高事件的发展是准双周尺度和季节内尺度动量输送共同作用的结果,不同的是超长阻高事件中准双周尺度动量输送集中在发展阶段前期,季节内尺度动量输送贯穿整个发展阶段,而其他阻高事件中动量输送相对较小。维持阶段超长阻高事件以定常动量通量的季节内尺度分量为主,其他阻高事件则以定常动量通量的准双周尺度分量为主。
