2022年我国夏季极端高温阶段性特征及成因

Stage Characteristics and Mechanisms of Extreme High Temperature in China in Summer of 2022

利用常规观测和自动气象站加密观测资料以及ERA5再分析资料分析2022年夏季我国大范围极端高温阶段性特征及其热动力成因,结果表明:此次极端高温存在两个不同阶段:6月高温区集中在华北黄淮地区,7—8月高温区位于四川盆地—长江中下游地区;两个阶段极端高温均发生在异常环流背景条件下,对流层上层为显著偏强的南亚高压控制区,其主导系统分别为500 hPa强烈发展的华北高压脊和异常强盛的副热带高压坝;Rossby波能量自上游向华北地区持续频散和瞬变天气扰动偏弱是华北高压脊增强和维持的主要成因,西北太平洋副热带高压南侧的大气热源增强、赤道附近热带辐合区异常偏强的上升气流在30°N副热带高压脊线附近下沉,有利于西北太平洋副热带高压的西伸加强且稳定维持。对流层低层强烈暖平流和边界层非绝热加热是华北黄淮地区高温形成的主要影响因子,高温的维持主要依靠异常强烈的非绝热加热;四川盆地—长江中下游地区高温的形成受深厚对流层内异常下沉增温和边界层内非绝热加热共同影响,高温长时间维持的影响因子除非绝热加热外,极端强盛的南亚高压控制区内异常绝热加热项(下沉增温)的贡献亦不可忽视。

Stage characteristics and thermodynamic mechanisms of the extreme high temperature in China in summer of 2022 are analyzed with conventional observations,automatic weather station observations and the fifth-generation European Centre for Medium-Range Weather Forecasts(ECMWF)atmospheric reanalysis data(ERA5).It shows that the extreme high temperature process has two different stages.In June,high temperature areas are concentrated in North China and Huanghuai Region.From July to August the high temperature weather remains stable in Sichuan Basin and the middle and lower reaches of the Yangtze River.The influence area,intensity and duration of the high temperature from July to August are significantly stronger than those in June.Two stages of extreme high temperature occur in the anomalous circulation background.The South Asian high controls the upper troposphere with significant positive anomaly.Dominant systems are the strong development of high pressure ridge in North China and the stable maintenance of the evidently strong high-pressure dam in subtropical regions.The sustained dispersion of Rossby wave energy from upstream to North China and the weakening of transient weather disturbances are main causes for the enhancement and stability maintenance of the North China high pressure ridge.The strong convection in tropical regions,the enhancement of atmospheric heat sources on the southern side of the Northwest Pacific subtropical high,the strong updraft near the intertropical convergence zone and sinking in subtropical high ridge line near 30°N are conducive to the westward extension,strengthening,and stable maintenance of the Northwest Pacific subtropical high.The thermodynamic diagnostic analysis shows that the strong warm advection in the lower troposphere and the diabatic heating anomaly in the boundary layer above than the climatology is the main cause of the high temperature in North China and Huanghuai Region,and the maintenance of high temperature mainly relies on the contribution of strong diabatic heating.The formation of the extreme high temperature in Sichuan Basin and the middle and lower reaches of the Yangtze River is caused by subsidence warming anomaly which is in the low troposphere and stronger than the climatology.The second stage of the high temperature is also affected by the diabatic heating anomaly in the boundary layer.Besides the diabatic heating,the contribution of adiabatic heating(subsidence warming)term in the extremely strong South Asian high control region cannot be ignored.