西南地区夏季高温热浪时空分布特征及其成因

利用98个测站逐日最高气温资料和ERA-interim再分析数据集,对1979~2018年西南地区夏季高温热浪的时空分布特征及其年际变化异常成因进行研究。结果表明:(1)气候平均西南地区夏季高温热浪频次从东南向西北减少,空间差异显著。近几十年来,西南地区高温热浪总体上显著增多,并表现出明显的年际和年代际变化特征。(2)EOF分解第1模态主要表现为全区一致型,可以反映西南地区夏季高温热浪变化的主要特征。第2模态空间分布大致呈现出南正北负的反相变化特征。(3)西南地区高温热浪偏多可能与对流层中层青藏高原以东至朝鲜半岛的明显高压异常相联系。在这个高压异常的控制下,西太平洋副热带高压向西移动,这有利于西南地区降水减少,云量减少,到达地表的太阳短波辐射增加。同时,东亚西风急流位置北移,可以阻止来自中高纬的冷空气入侵西南地区,引起这里降水减少干旱频发。最终,异常干燥和炎热的地表条件,与有利的大气环流背景相配合,从而造成西南地区夏季高温热浪事件的发生。 

Spatial-Temporal Characteristics and Causes of Summer Heat Waves in Southwest China

Southwestern China(SWC) has experienced more frequent heat waves in recent summers. In this study,we discussed the temporal and spatial variation characteristics of summer heat waves over Southwest China and its possible causes on the interannual time scale,based on the daily observational summer maximum temperature data at 98 stations and ERA-interim reanalysis dataset from 1979 to 2018. The results indicate that the spatial distribution of climatic frequency of summer heat waves(HWF) is generally characterized by less in northwestern and more in southeastern SWC. The first mode features HWF increases over most of SWC except northwestern Yunnan province,which can reflect the main distribution characteristic of the HWF,and the second mode exhibits less HWF in the north but more HWF in the south part. It is suggested that the increasing SWC summer heat waves are correlated with the obvious abnormal high pressure from the east of Tibet Plateau to the Korean Peninsula at middle troposphere. Under the control of this high pressure anomaly,the western Pacific subtropical high moved westward,which is conducive to the decrease of precipitation in the SWC,the decrease of cloud cover,and the increase of solar shortwave radiation reaching the surface. At the same time,the position of the East Asian Westerly Jet moves northward,which can prevent cold air from mid-high latitudes invading the southwest region,causing frequent droughts in the SWC. Finally,the unusually dry and hot surface conditions,combined with the favorable atmospheric circulation conditions,lead to the occurrence of summer heat waves over SWC.