次季节变率和“北极增暖-欧亚变冷”的趋势

Subseasonal variability and the“Arctic warming-Eurasia cooling”trend

“北极增暖-欧亚变冷”的趋势显著影响了中低纬度地区的天气形态以及极端气候变化.然而,从2012年至2021年冬季,这一趋势显著减弱.与此同时,“暖北极-冷欧亚”(WACE)与其相反位相“冷北极-暖欧亚”(CAWE)模态之间的次季节位相转换频率显著增加,并且WACE/CAWE的次季节强度与1996-2011年可比.长期的再分析数据以及CMIP6模拟数据均支持频繁的WACE/CAWE次季节反转与“北极增暖-欧亚变冷”趋势减弱同时发生.前期热带大西洋海温和印度洋海温异常分别对前冬和后冬的WACE/CAWE有显著且主要的影响,并在CAM5和AMIP的数值实验中得到有效验证.两个海温的协同作用有效地调节了WACE和CAWE之间的次季节相位转换,正如2020和2021年冬季所发生的那样.本研究结果表明中低纬度地区极端气候预测中同样需要考虑次季节变率.

The“Arctic warming-Eurasia cooling”trend has significantly affected the changes of weather patterns and climate extremes at lower latitudes and has attached huge attentions.However,this winter trend weakened from 2012 to 2021.In the same time period,subseasonal reversals between the warm Arctic-cold Eurasia(WACE)and cold Arctic-warm Eurasia(CAWE)patterns became more frequent and the subseasonal intensity of the WACE/CAWE pattern was still comparable with that from 1996 to2011.This study highlighted the co-occurrence of this subseasonal variability and trend changes in the WACE/CAWE pattern based on long-term reanalysis datasets and Coupled Model Intercomparison Project Phase 6 simulations.The preceding sea surface temperature anomalies in the tropical Atlantic and Indian oceans had significant primary impacts on the WACE/CAWE pattern in early and late winter,respectively,which were confirmed by numerical experiments based on the Community Atmosphere Model and Atmospheric Model Intercomparison Project.Their coordination worked to effectively modulate the subseasonal phase reversal between the WACE and CAWE patterns just like what happened in the winters of 2020 and 2021.Findings of the present study imply that subseasonal changes need to be considered in the prediction of climate extremes at mid-to low latitudes.