2018年夏季辽宁异常高温干旱的环流特征及成因

利用NCEP/NCAR逐日再分析资料和辽宁省53站逐日降水量及日平均气温资料，采用诊断分析方法，研究了2018年夏季辽宁异常高温干旱的环流特征及成因。结果表明：2018年夏季辽宁发生了1962年以来最严重的高温干旱事件。辽宁地区上空受相当正压结构的异常反气旋性环流控制，是异常高温干旱发生的局地环流成因；异常反气旋性环流南侧存在一个异常气旋性环流，阻挡了孟加拉湾和南海地区西南暖湿气流向辽宁地区输送，不利于辽宁地区产生降水。南亚高压和西太副高相向运动并在辽宁地区上空重叠，是异常高温干旱发生的大尺度环流成因。EAP/PJ型和EU型遥相关是西太副高异常发展的直接原因。准定常Rossby波能量频散是导致EAP/PJ型和EU型遥相关形成与维持的根本原因之一。源自北大西洋地区的Rossby波能量，沿西风急流波导区向下游频散，使得包括辽宁在内的我国北方广大地区位势高度异常增强；同时我国东北至朝鲜半岛和日本一带存在Rossby波能量的准经向频散，同样有利于EAP/PJ型遥相关的维持与发展，使得辽宁及其附近地区上空受位势高度正距平控制。

Analysis of circulation characteristics and cause of anomalous high temperature and drought in summer of 2018 over Liaoning

Based on the NCEP/NCAR daily reanalysis product and daily precipitation and temperature data collected at observational stations,the circulation characteristics and causes of anomalous the high temperature and drought in the summer of 2018 over Liaoning Province have been investigated using a diagnostic analysis method.The results demonstrate that in the summer of 2018 Liaoning Province experienced a record-breaking event since 1962.The precipitation in the entire region showed a negative anomaly,and the anomalous precipitation was -127.72 mm.The precipitation anomaly percentage in the western and eastern parts of Liaoning Province was 10%~30%,while that in the central part was 30%~60%.In particular,the precipitation anomaly percentage in the northern and southern parts of Liaoning Province was less than 60%.Meanwhile,unusually high temperature influenced Liaoning Province mainly from mid-July to early August.The high temperature was developing from the northeastern part of Liaoning Province and gradually spreading to the southwestern part while strengthening in intensity,and reaching its peak in early August.The temperature in the northern part of Liaoning Province was more than 2.4 degrees greater than its mean climatology;that in the central part was more than 3.2 degrees greater;and that in the southern part was more than 4 degrees greater.Under the influence of abnormally high temperature and abnormally low rainfall,the drought situation in Liaoning Province intensified rapidly.The anomalous anticyclonic circulation with equivalent barotropic structure is the local circulation cause.Liaoning Province was controlled by an abnormal anticyclone from the lower troposphere to the upper troposphere.The anomalous cyclonic circulation on the southern side of the anomalous anticyclonic circulation blocks the warm and humid airflow from the Bay of Bengal and South China Sea to Liaoning Province,which is conducive to precipitation in Liaoning Province.Moving in opposite directions of the South Asia High(SAH) and Western Pacific Subtropical High(WPSH) and overlapping over Liaoning Province was the large-scale circulation caused by the hot and drought-ridden summer of 2018.As a result,Liaoning Province was continuously affected by the downdraft.The East Asia Pacific/Pacific Japan (EAP/PJ) and Eurasian (EU) pattern was one of the direct causes for the abnormal development of the WPSH.The positive geopotential height anomaly center in Liaoning Province was strengthened by the EAP/PJ and EU pattern,thus contributing to the northward positioning of the WPSH.The dispersion of Rossby wave energy is one of the fundamental causes for the formation and perpetuation of the EAP/PJ and EU pattern.The Rossby wave energy originating from the North Atlantic dispersed eastward to East Asia along the waveguide area of the high-altitude westerly jet,thereby resulting in the abnormal enhancement of the geopotential height in northern China,including Liaoning Province.Meanwhile,there was a quasi-meridional dispersion of Rossby wave energy from northeastern China to the Korean Peninsula and Japan,which is conducive to maintaining and developing the EAP/PJ and EU pattern,thus making Liaoning Province controlled by a positive geopotential height anomaly,and in turn the WPSH developed abnormally.The persistence of the heat and drought event over Liaoning Province was due to the perpetuation of the quasi-stationary waves at mid-high latitudes,which originated from the North Atlantic Ocean.