青藏高原与周边地区近四十年区域夏季地表气温变化趋势的异同及归因分析

Difference/Similarity and Attribution of Changes in Regional Summer Surface Air Temperatures over the Tibetan Plateau and Its Surrounding Regions in the Past 40 Years

欧亚大陆夏季地表气温在近四十年有显著的升温趋势,本文基于ERA5再分析数据研究了1979~2019年间欧亚大陆不同区域的夏季地表气温的变化特征,并利用气候反馈响应分析方法揭示了各区域变暖原因的异同。作为全球海拔最高的大地形,青藏高原在过去四十年经历了显著的增温过程。青藏高原周边相对低海拔的地区(如北非—南欧地区、蒙古地区、东北亚地区)同样表现出明显的变暖特征,而高原南侧的南亚地区的地表气温却变化不明显。青藏高原夏季积雪融化引起的地表反照率减小使得更多短波辐射到达地表,放大高原地表增暖。北非—南欧地区增暖则主要源于大气气溶胶含量减少造成的入射短波辐射增加。同时,大气温度升高导致的向下长波辐射增强对北非—南欧地区以及蒙古地区的增暖都有显著贡献。此外,东北亚地区云的减少是造成其地表增暖最主要的过程,而南亚地区则是水汽增加和感热通量减少造成的增温与云和气溶胶增加造成的降温相抵消,因而温度变化幅度不大。

The summer surface air temperatures over Eurasia have exhibited significant warming trends in recent decades.Based on the European Centre for Medium-Range Weather Forecasts Reanalysis version 5(ERA5)data,this study investigates the characteristics of the changes in summer surface temperatures over different Eurasian regions during 1979–2019,reveals the similarities and differences among various regions,and explains the contributing factors by adopting a climate feedback response analysis method.As the highest terrain in the world,the Tibetan Plateau(TP)has experienced a remarkable warming trend in the past several decades.The lower-elevation regions surrounding the TP,such as North Africa,Southern Europe,Mongolia,and Northeast Asia,also show obvious warming features.Meanwhile,the surface temperature does not change significantly in South Asia to the south of the TP.The decreased summer surface albedo due to melting snow enables more incoming shortwave radiation to reach the surface,amplifying surface warming over the TP.Warming over North Africa and Southern Europe is mainly attributed to the increase in shortwave radiation due to reduced aerosols.Meanwhile,the increase in downward longwave radiation caused by increased atmospheric temperature significantly contributes to warming over North Africa,Southern Europe,and Mongolia.Moreover,the reduction in clouds is the main factor contributing to surface warming over Northeast Asia.In South Asia,warming induced by increased atmospheric water vapor and decreased surface sensible flux is offset by cooling because of increases in clouds and aerosols,leading to small long-term changes in the regional summer surface temperature.