2020年夏季华南高温热浪时空特征及其成因分析研究

Spatiotemporal Characteristics and Physical Mechanisms of the Summer High Temperature Heat Waves over South China in 2020

关键词:  高温热浪  南亚高压  高空西风急流  对流活动  Rossby波列

Key words:  high temperature events  South Asian high pressure  upper-level westerly jet stream  convective activities  Rossby wave trains

摘要:

基于1960—2020年华南地区183个气象站和NOAA/CPC逐日最高气温、NCAR/NCEP日再分析资料，采用百分位法提取华南地区区域性高温热浪事件，分析其时空变化特征及可能的物理机理。结果表明：（1）与1991—2020年气候态和2003年相比，2020年夏季华南区域性高温日开始时间偏早、结束偏晚、高温日数偏多和高温热浪事件发生频次偏多。2020年夏季共有4次区域性高温热浪事件，第2、3次事件偏湿且持续时间最长，高温日数占比为64.2%（34天/53天）。（2）2020年夏季高温期南亚高压偏强偏东、高空西风急流偏强偏东和副高偏强偏西，华南地区受异常反气旋环流控制。在欧亚大陆中高纬度地区第2、3次事件中200hPa位势高度异常为“西低东高”、第1、4次事件则为“西高中低东高”分布型。（3）海温异常偏暖是华南高温高湿的重要前兆因子，2020年华南高温期间大气以偏湿为主，与春季—盛夏印度洋、热带大西洋、西北太平洋和东北太平洋海温持续性一致偏暖有关，激发从欧亚中西部向东传播到东亚大陆的Rossby波列，有利于夏季东亚地区维持南亚高压偏强偏东、高空西风急流偏强偏东和副高强盛且西伸的大气环流异常结构，华南地区受异常反气旋环流控制，诱发持续性高温高湿热浪事件。

Abstract:

Based on the daily maximum temperature from 183 ground stations in South China and NOAA/ CPC gridded datasets and NCAR/NCEP reanalysis data during 1960-2020, this study identifies regional- level heatwave events (HWEs) in South China by applying a percentile analysis method, and investigates their spatiotemporal characteristics and underlying physical mechanisms. The results revealed that: (1) Compared to the 1991-2020 climatological average state and the 2003 summer HWEs in South China, the 2020 summer HWEs exhibited earlier onset and later termination, with high frequency of the highwave day (HWD) and HWE. Four strong regional HWEs occurred during summer 2020, with the second and third HWEs being wetter and persisting longest, and accounting for 64.2% (34 days /53 days) of the HWDs. (2) In 2020 heat episodes, the South Asian high pressure (SAHP) was strong and eastward, the upper-level jet stream (ULJS) was strong and eastward, and the Northwest Pacific high pressure (NWPHP) was strong and westward. The South China region was controlled by abnormal anticyclonic circulation. In the mid- and high-latitude Eurasian continent, the second and third HWEs showed "west-low/east-high" patterns in summer 2020, with the first and fourth HWEs exhibiting a "high-low-high" pattern. (3) The abnormally warm sea surface temperature is an important precursor factor for high temperature and high humidity in South China. During the 2020 high temperature period in South China, the atmosphere was mainly humid, which is related to the sustained warm sea surface temperature in the Indian Ocean, tropical Atlantic, northwest Pacific, and northeast Pacific from spring to summer. It triggered Rossby wave trains that spread eastward from central and western Eurasia to the East Asian continent, which is conducive to maintaining the strong eastward SAHP, strong eastward ULJS, and NWPHP intensity and westward extension of atmospheric circulation in East Asia during summer. The South China region is controlled by abnormal anticyclonic circulation, triggering sustained high temperature and high humidity heat waves.