Abstract: The regional high temperature weather process happened in Chongqing from 16 July to 7 August 2017, and it was the strongest since 1968. Based on the daily observation data at 34 weather stations of Chongqing, NCEP/NCAR reanalysis data and feature indexes of subtropical high from National Climate Center of China, the circulation characteristics and possible disturbance mechanism in the atmosphere during the high temperature weather process were diagnosed and analyzed. Compared with the normal, the water vapor transport was weaker in low layer of troposphere, the subtropical high was stronger and westward persistently in middle layer, and the frequency and intensity of cold air were lower and weaker and the westerlies was weaker and northward in high layer. Moreover, the South Asia high was stronger and caused the subtropical high westward and northward. These anomalous circulation situations caused the high temperature weather process in Chongqing. Compared to the top 10 regional high temperature processes in history, the atmospheric circulation in middle and high layers of troposphere was straighter over middle and high latitudes from 16 July to 7 August 2017, the trough and ridge weren’t obvious, and the geopotential height was consistently higher from the tropical to high latitude. The water vapor budget over Chongqing and its surrounding still presented the input of water vapor during the high temperature weather process, but the value was significantly smaller than the normal. The regional average divergence during the high temperature weather process was different from the climatology mean, it presented the divergence with 2.30×10-7 kg·s-1·m-2, and the intensity was stronger than the normal (-1.3×10-8 kg·s-1·m-2). Therefore, Chongqing was in the control of less water vapor transport and stronger downdraft airflow for a long time, which was beneficial to the formation of high temperature and less rainfall weather.

Key words: regional high temperature, circulation diagnosis, subtropical high, Chongqing

摘要： 2017年7月16日至8月7日重庆市出现1968年以来最强的一次区域性高温天气过程。利用重庆市34个站点逐日气象观测资料、NCEP/NCAR逐日再分析资料以及国家气候中心副高特征指数资料等，对此次区域性高温过程的环流特征、可能的大气内部扰动机制进行诊断分析。结果表明：对流层低层水汽输送偏弱，中层副热带高压持续偏强、偏西，高层西风带偏弱、偏北，冷空气活动次数少且偏弱以及南亚高压偏强促使副高西进北抬，这种异常的环流形势引发了此次区域性高温天气过程。与历史上较为突出的区域性高温过程相比，此次高温过程期间中高纬度地区对流层中高层环流较为平直，无明显的槽脊发展，低纬热带至中纬度地区位势高度一致性偏高。重庆及周边地区水汽收支仍为水汽输入，但较常年明显偏弱，且散度场上表现为辐散，较常年辐合值明显偏强。可见，重庆地区长时间处于水汽输送偏少、下沉气流偏强的环流形势控制下，从而形成高温少雨天气。

关键词: 区域性高温, 环流诊断, 副高, 重庆市