2018年夏季东北极端高温事件物理机制分析

Analysis on the Mechanism of the 2018 Summer Extreme High Temperature Event in Northeast China

基于观测资料和再分析资料,研究分析了2018年夏季中国东北地区持续多日出现高温异常事件的形成机理。首先分析了整个夏季该地区观测台站逐日的温度资料,计算了观测台站的超热因子(Excess Heat Factor,EHF)指数,发现东北地区出现高温异常的时段主要是7月和8月,异常高温的发生区域集中在东北南部。在此期间,东亚大气环流形势的异常主要表现为南亚高压和西太平洋副热带高压强度异常增强,作用相互重叠和位置持续偏北。进一步的分析可以注意到,二者的重叠造成研究区域内有负涡度异常增强,使得南亚高压和西太平洋副热带高压在北推的过程中不断带动东北南部上空负涡度异常增强,并伴随有异常下沉气流,下沉绝热增温与晴空辐射增温,这可能是东北南部地表增温的一个重要原因。相关分析证实,在整个夏季东北南部地表气温与其上空300 hPa至500 hPa涡度异常都有显著的负相关关系。因此,南亚高压和西太平洋副热带高压之间的相互叠加组合是导致东北南部在2018年夏季7、8月份出现高温异常的主要原因。进一步的研究发现,夏季副热带西风急流中准定常Rossby波能量的传播与南亚高压和西太平洋副热带高压异常增强有密切联系,同时夏季西太平洋暖池的显著增暖导致了菲律宾地区异常旺盛的对流活动,进而在500 hPa高度场上激发出PJ(太平洋—日本涛动)波列,从另一个路径上促进了西太平洋副热带高压偏强偏北。

The mechanisms involved in the development of high temperature anomalies in Northeast China during the summer of 2018 were studied using observational and reanalysis data.First,daily temperatures recorded at observation stations in the region throughout the summer were analyzed.Next,the excess heat factor index of the observation stations was calculated.July and August were the main anomaly high temperature periods when high temperature anomalies occurred in the southern part of Northeast China.The South Asia high(SAH)and western Pacific subtropical high(WPSH)were significantly intensified during this period,and overlapped with each other on different levels and extended northward.There was also an increase in the negative vorticity anomalies in the overlapping area of the SAH and WPSH,and the two northward extending systems continued to drive the negative vorticity anomalies.In addition,an abnormal down draft occurred over the southern part of Northeast China together with sinking adiabatic warming and clear-sky radiation warming,which may have been important factors involved in surface warming in this area.Furthermore,surface temperature anomalies were significantly correlated with negative vorticity anomalies at geopotential heights from 300 to 500 hPa during the summer of 2018 in this region.It was also determined that the quasi-stationary Rossby wave energy propagation in the summer subtropical westerly jet was closely related to the anomalous enhancement of the SAH and WPSH.Significant simultaneous warming of the western Pacific warm pool during the summer also promoted unusually strong convective activity in the Philippines.The Pacific–Japan(PJ)wave train was excited at a geopotential height field of 500 hPa,which also led to the enhancement and northward extension of the WPSH.In summary,the existence of the SAH and WPSH and their overlapping were the main causes of the high temperature anomalies in the southern part of Northeast China during July and August 2018.