2004年安徽省梅汛期三次暴雨过程的大气低频振荡背景

对2004年夏季安徽省降水以及850 hPa涡度、水汽通量散度场进行Morlet小波分析，结果发现:6月中下旬，三者都存在着2~6 d，7~15 d以及18~30 d的振荡周期，并且三者的各频带的低频分量与实际降水距平的对应关系较好。其中18~30 d低频涡旋系统和水汽通量散度具有源自孟加拉湾和中南半岛自西南向安徽省传播特征；7~15 d低频涡旋系统主要是沿着中纬度地区自西向东传入安徽省，低频水汽通量散度则由低纬度地区自南向北传入安徽省。6月中下旬赤道西太平洋地区沿东南-西北向移动的7~15 d低频气旋和反气旋波列，以及安徽省附近低层流场的2~6 d高频变化，为其6月中下旬的三次强降水过程提供了有利条件。

Analysis of Low Frequency Oscillations of Three Rainstorms during the Period of Meiyu in 2004 of Anhui

In terms of wavelet, vortex and moisture flux divergence analyses, study is undertaken of 2004 rainstorms from June to August in Anhui. Results show that the elements exhibit significant 2-6 d, 7-15 d and 18-30 d oscillations. The variations of 2-6 d and 7-15 d oscillations of these elements are almost consistent with the anomaly of precipitation from mid-June to later-June. The vortex of the 7- 15 d oscillation moves towards Anhui along the mid-latitude from west to east, and the moisture flux divergence of the 7-15 d oscillation moves towards Anhui from low-latitudes. The cyclone and anticyclone wave trains of the 7- 15 d oscillation moves towards northwest over the equatorial west Pacific Ocean and the high frequency change of the streamline field at low levels provide favorable conditions for Anhui rainstorms in June 2004