ENSO对中国东部前后冬天气尺度气温变率的不同影响及其可能机制

Different ENSO impacts on early and late winter synoptic-scale air temperature variability over eastern China and possible mechanisms

基于中国国家气象信息中心提供的中国第一代全球大气和陆面再分析产品(CRA)的逐日气温资料、美国国家海洋和大气管理局(NOAA)重建的逐月海表温度资料以及美国国家环境预报中心/国家大气研究中心(NCEP/NCAR)提供的大气环流再分析资料,研究了厄尔尼诺-南方涛动(ENSO)对中国东部前、后冬天气尺度气温变率的影响及其物理机制。结果表明,ENSO对中国东部天气尺度气温变率的影响在前、后冬存在显著差异。ENSO对前冬中国东部天气尺度气温变率影响较弱,后冬则显著增强。后冬时期,ENSO与长江中下游地区天气尺度气温变率呈现显著正相关,即厄尔尼诺年后冬天气尺度气温变率增强,气温波动幅度增大;拉尼娜年后冬天气尺度气温变率减弱,气温变化较为平缓。ENSO在后冬可通过影响与欧亚大陆上空南北温度梯度相关的大气斜压性调节下游东亚地区大气环流的天气尺度变率,进而影响天气尺度气温变率。厄尔尼诺年后冬,南北温度梯度大,大气斜压性较强,经向风活跃,冷空气活动较为频繁,天气尺度气温变率增大;拉尼娜年后冬,异常情况与之大致相反。在前冬ENSO对欧亚大陆上空南北梯度即大气斜压性影响较小,因而对中国东部天气尺度气温变率的影响也较弱。本研究的成果丰富了对ENSO影响中国气温变率的理解,有利于中国冬季气温季节预测水平的提升。

Based on daily mean air temperature data from the first-generation global atmosphere reanalysis product(CRA)of China,the reconstructed monthly sea surface temperature data from National Oceanic and Atmospheric Administration(NOAA),and the National Centers for Environmental Prediction/National Center for Atmospheric Research(NCEP/NCAR)atmospheric circulation reanalysis data,the present study investigates influences of El Niño-Southern Oscillation(ENSO)on the early and late winter synoptic-scale air temperature variability over eastern China and possible mechanisms.It is revealed that the ENSO impacts differ remarkably between early and late winter.That is,the synoptic-scale air temperature response to ENSO over eastern China is weak in early winter but strong in late winter.In late winter,there is a significant positive correlation between ENSO and the synoptic temperature variability in the middle and lower reaches of the Yangtze river of eastern China.It suggests that the synoptic-scale air temperature variability and temperature fluctuation in late winters of El Niño(La Niña)years are usually stronger(weaker)than that in normal years.In late winter,ENSO can modulate the atmospheric baroclinicity by changing the meridional temperature gradient in the middle and high latitudes of Eurasia,which affects the synoptic-scale variation of atmospheric circulation in East Asia and subsequently affects the synoptic-scale air temperature variability over eastern China.Specifically,in late winters of El Niño years,the north-south temperature gradient is larger and the corresponding atmospheric baroclinicity is stronger,which could lead to more active meridional wind activities and more frequent cold air activities.Roughly opposite mechanisms apply during late winters of La Niña years.However,in early winter,ENSO has a weak influence on the meridional temperature gradient in the middle and high latitudes of Eurasia,and thus exhibits minor effects on the synoptic-scale temperature variability over eastern China.The results can enrich our understanding of the ENSO impact on air temperature variability in China,and provide references for improving seasonal prediction of wintertime air temperature over China.