重庆西部区域性阻塞型暴雨浅析

利用1981—2010年重庆市34个气象观测站的日(20时—20时)降水量资料及空间间隔为2.5°×2.5°的NECP/NCAR逐6小时再分析资料,对重庆西部区域性阻塞型暴雨天气过程进行统计合成分析,结果表明：(1)导致渝西阻塞型暴雨的大尺度环流背景场为稳定的“两槽一脊”型环流,贝加尔湖低槽与东移的四川盆地低槽同位相叠加,副高西伸并稳定维持,位势场呈现“西低东高”的特点；(2)来自于南海地区的水汽持续输送至重庆西部地区为暴雨过程的产生和维持提供了有利的水汽条件；(3)暴雨发生前后温湿场发生了明显变化,温度场上暴雨发生前和发生时暴雨区附近有着较强的暖平流,而暴雨发生后为明显冷平流,湿度场上700hPa上10g/kg等比湿线及850hPa上15g/kg等比湿线可作为渝西阻塞型暴雨的一个预报参考指标。

A Brief Analysis of Regional Blocking Rainstorm in Western Chongqing

Based on 34 meteorological observatories’daily (from 20:00 p.m. of the day to 20:00 p.m. of the next day) precipitation data in Chongqing from 1981 to 2010, and every 6 hour NCEP/NCAR reanalysis data with spatial resolution 2.5°×2.5°, the authors statistically used synthetic analysis method to study regional blocking rainstorm process in western Chongqing. The results were as follows: (1) the large-scale circulation background that led to regional blocking rainstorm process in western Chongqing was the steady‘two trough and one ridge’type, with the low trough of Lake Baikal and the low trough of the eastward Sichuan Basin having in- phase superposition, the subtropical high extending westward and maintaining stably, and the geopotential height field having the characteristics with‘lower value in the west and higher value in the east’; (2) the water vapor from the south China Sea was transported continuously to the western Chongqing providing favorable moisture condition for the generation and maintenance of the rainstorm process; (3) the temperature and humidity field both changed greatly after the rainstorm process; relatively strong warm advection existed around the rainstorm area before and during the rainstorm process, while obvious cold advection took its place after the process. The constant specific humidity line of 10 g/kg in 700 hPa and 15 g/kg in 850 hPa could be used as forecast reference indexes for the blocking rainstorm in western Chongqing.