CMIP6模式未来情景下模拟的大气质量季节循环:非线性变化

Simulated seasonal cycle of atmospheric mass in four future scenarios of the CMIP6 models:a nonlinear response to increasing greenhouse gases

摘要:

全球持续增暖背景下南北半球大气质量呈现出明显的异常变化。利用2015—2100年CMIP6资料,分析了4个温室气体排放情景下大气质量季节循环特征,并比较不同情景下地表气压和极涡变化特征,结果表明:不同情景下全球及半球面积平均大气质量的气候平均值季节变化位相相同,且与历史模拟试验的分布一致。随着温室气体排放量的逐步增加,全球大气质量年变程逐渐增大,然而南北半球大气质量和南北涛动年变程并非逐步增大,而是有起有伏。这种非线性现象主要表现为:在SSP1-2.6、SSP3-7.0情景下南北半球大气质量和南北涛动的年变程较小,而在SSP2-4.5、SSP5-8.5情景下其年变程较大。对应这种起伏,在地表主要表现为北太平洋、北大西洋地表气压在SSP2-4.5和SSP5-8.5情景下增高与在SSP1-2.6和SSP3-7.0情景下降低,以及南半球45°S以南地表气压发生变化;在垂直方向上,主要表现为南北极平流层极涡随温室气体排放持续增加而呈现强弱交替的非线性变化。

Abstract:

In the context of global warming,future climate projections have become a major research focus.The increasing greenhouse gas (GHG) emissions in the CMIP6 scenarios-SSP1-2.6,SSP2-4.5,SSP3-7.0,and SSP5-8.5 are accompanied by rising global mean surface air temperatures.However,the potential changes in the seasonal cycle of atmospheric mass,particularly the annual range,remain an open scientific question.This study analyzes CMIP6 data from 2015 to 2100 to examine the seasonal cycle characteristics of atmospheric mass under four GHG emission scenarios compared to historical runs.The study also examines the spatial distribution of surface air pressure and geopotential height in February and July,interpreted through temperature and wind fields.The results reveal that while the seasonal variations of global and hemispheric average atmospheric mass in the different scenarios resembles those in historical simulations,the annual range of hemispheric air fluctuates rather than increasing uniformly with higher GHG emissions.Specifically,the annual range decreases in SSP1-2.6 and SSP3-7.0,while it increases in SSP2-4.5 and SSP5-8.5.Globally,the annual range of atmospheric mass increases steadily with higher GHG emissions.Surface air pressure and geopotential height distributions in future scenarios align with reanalysis data,but in the Northern Hemisphere,a phase transition emerges,linked to the land-sea distribution dominated by Eurasia,the North Pacific,and the North Atlantic.In contrast,the Southern Hemisphere phase transitions occur along the latitudinal zones.The alternating positive and negative values in the February-July difference suggest regionally varying trends and amplitudes of change in surface air pressure and wind fields due to GHGs.These regional differences contribute to variations in the annual range of surface air pressure across the hemispheres.With increasing GHG emissions,the Northern and Southern Hemispheres respond differently across seasons,and this variation is evident not only in the lower troposphere but also at higher altitudes,including the stratosphere.The Arctic and Antarctic stratospheric vortices show nonlinear changes in intensity,weakening and strengthening in cycles as GHG emissions rise.These results suggest that the uneven distribution of GHGs in the atmosphere leads to variable temperature responses at different altitudes,altering the geopotential potential height field,layer thicknesses,and,consequently,surface air pressure.This highlights the region-specific response of atmospheric mass to increasing GHGs.The CMIP6 simulations provide valuable insights into atmospheric circulation changes under the conservation of atmospheric mass and their impacts on weather and climate in a warming world.Additionally,the nonlinear effects of human activities on water vapor mass and the atmospheric water-holding capacity deserve further exploration,particularly regarding their influence on the annual range of atmospheric mass.It remains uncertain whether transient and stable warming scenarios will lead to different outcomes in air mass changes.