Influences of tropical circulation and sea surface temperature anomalies on extreme heat over Northeast Asia in the midsummer of 2018

2018年盛夏东北亚地区遭受了严重的高温热浪袭击。同时,西北太平洋地区出现了研究时段内最强的气旋环流异常,热带海温的异常信号在热带太平洋和北印度洋均很弱,而热带东南印度洋呈现明显的冷异常。针对2018年盛夏的独特现象,本文研究了热带东南印度洋和热带大气环流对东北亚高温的影响。结果表明,热带东南印度洋冷海温激发异常的越赤道气流和局地经圈环流,有利于西北太平洋出现气旋异常。进一步,西北太平洋气旋异常通过局地经圈环流在东北亚地区造成异常下沉和反气旋,从而有利于东北亚高温发生。

A destructive extreme heat attacked Northeast Asia(NEA)in the midsummer of 2018,characterized by the average midsummer Tmax(daily maximum air temperature at 2 m)ranking first during the study period.The current study indicates that the cyclonic anomaly over the western North Pacific(WNP)was an important cause,which presents an anomaly of two standard deviations.The cyclonic anomaly over the WNP was accompanied by anomalous convection,which favored descending and anticyclonic anomalies over NEA through a local meridional cell.The anticyclonic anomaly over NEA corresponds to the northwestward extension of the WNP subtropical high and facilitated the occurrence of extreme heat.The tropical sea surface temperature anomaly(SSTA)presents a La Ni?a decaying episode,but the SSTA over the tropical Pacific and North Indian Ocean was weak in the summer.In contrast,the southeastern tropical Indian Ocean(SETIO)was obviously cool,which was the coolest after detrending.The SETIO cooling triggered a low-level southeasterly anomaly,which turned into a southwesterly after crossing the equator,due to the Coriolis force.The southwesterly anomaly extended eastwards and favored the cyclonic anomaly over the WNP.Meanwhile,the circulation anomalies over the SETIO and WNP were connected via a local meridional cell,with the ascending branch over the WNP.Moreover,the above mechanism also operates for the climate statistics,verifying the robust in?uence of the SETIO SSTA.Considering the consistency of the SETIO SSTA,it could be a potential predictor for the climate over the WNP and NEA.