2022年永州地区两次强降水过程对比分析

Comparative Analysis of Two Heavy Rainfall Processes in Yongzhou in 2022

摘要: 本文利用自动站实况降水观测资料、NCEP再分析资料以及探空资料，分别对2022年5月29~30日以及6月4~6日永州地区的两次强降水天气过程从实况、环流形势、水汽条件、动力条件、热力条件以及不稳定能量方面进行了对比分析，结果表明：两次强降水过程均受空中槽以及地面锋面系统过境影响，第一次过程降水强度较大且降水分布范围较广，覆盖永州大部地区，第二次降水过程持续时间较长，强度相较于第一次过程较弱，且主要集中在永州中部以及北部地区，分布范围相对较小；与第一次降水过程相比，第二次降水过程天气系统维持时间较长，强度相较于第一次较弱；水汽条件方面，两次强降水过程中永州地区的水汽辐合过程均较为显著，为强降水的持续提供了有利水汽条件。第二次强降水过程中，水汽通量散度大值区分布范围更广，但中心强度较低，且第二次降水过程中整层大气可降水量以及比湿大值区分布范围也较广，表明第二次强降水过程期间大气湿度较大，降水持续时间较长；动力条件方面，两次强降水过程，在永州地区均出现低空辐合、高空辐散运动，其产生的抽吸作用利于垂直上升运动的加强和维持，为强降水天气的发生发展提供了较为有利的动力条件，第一次强降水过程中，永州地区上空垂直速度以及散度场的变化更快，大气垂直运动更为剧烈，湍流运动更强，且大气的辐合区更为深厚，这也表明第一次强降水过程大气的不稳定度更高，降水过程更为集中，而第二次降水过程强度较弱；热力条件方面，对比分析发现这两次强降水天气过程，均具有较为有利的高温高湿的不稳定条件，而在第二次的强降水天气过程中，其假相当位温以及K指数大值区分布范围更广，且持续时间更长，表明第二次降水过程的持续时间也较长；不稳定能量方面，在这两次强降水过程期间，永州地区上空均积累了大量不稳定能量，为强降水的发生发展提供了较为有利的动力以及热力条件，与第二次强降水过程相比，第一次强降水天气过程中，永州地区上空的不稳定能量更为深厚，表明其降水过程强度更强，降水更为集中。

Abstract: In this paper, the formation and development process of two heavy precipitation weather processes in Yongzhou area on May 29~30 and June 4~6,2022 were compared and analyzed from the aspects of actual situation, circulation situation, water vapor condition, dynamic condition, thermal condition and unstable energy by using the actual precipitation observation data of automatic station, NCEP reanalysis data and sounding data. The results show that the two heavy precipitation processes are affected by the transit of air trough and surface frontal system. The precipitation intensity of the first process is large, and the distribution range of precipitation is wide, covering most areas of Yongzhou, and the duration of the second precipitation process is long. The intensity is weaker than the first process and is mainly concentrated in the central and northern regions of Yongzhou, with a relatively small distribution range. Compared with the first precipitation process, the weather system of the second precipitation process lasted longer and the intensity was weaker than that of the first precipitation process. In terms of water vapor conditions, the water vapor convergence process in Yongzhou area during the two heavy precipitation processes is more significant, which provides favorable water vapor conditions for the continuation of heavy precipitation. During the second heavy precipitation process, the large value area of water vapor flux divergence is wider, but the center intensity is lower, and the large value area of precipitable water vapor and specific humidity in the whole atmosphere during the second heavy precipitation process is also wider, indicating that the atmospheric humidity during the second heavy precipitation process is larger, and the precipitation duration is longer. In terms of dynamic conditions, low-altitude convergence and high-altitude divergence occurred in Yongzhou during the two heavy rainfall processes. The pumping effect was conducive to the strengthening and maintenance of vertical ascending motion, which provided favorable dynamic conditions for the occurrence and development of heavy rainfall weather. During the first heavy rainfall process, the vertical velocity and divergence field over Yongzhou changed faster, the vertical motion of the atmosphere was more intense, the turbulent motion was stronger, and the convergence zone of the atmosphere was deeper, which also indicated that the atmosphere was more unstable during the first heavy rainfall process, the precipitation process was more concentrated, and the intensity of the second precipitation process was weaker. In terms of thermal conditions, comparative analysis found that these two heavy precipitation weather processes have more favorable unstable conditions of high temperature and high humidity. In the second heavy precipitation weather process, the distribution range of the pseudo-equivalent potential temperature and the large value area of the K index is wider, and the duration is longer, indicating that the duration of the second precipitation process is also longer. In terms of unstable energy, during the two heavy precipitation processes, a large amount of unstable energy was accumulated over Yongzhou area, which provided favorable dynamic and thermal conditions for the occurrence and development of heavy precipitation. Compared with the second heavy precipitation process, the unstable energy over Yongzhou area was deeper during the first heavy precipitation process, indicating that the precipitation process was stronger, and the precipitation was more concentrated.