1991年江淮特大暴雨与东亚大气低频振荡

LOW FREQUENCY OSCILLATION IN EAST ASIA DURING THE 1991 EXCESSIVELY HEAVY RAIN OVER CHANGJIANG-HUAIHE RIVER BASIN

本文分析了１９９１年江淮特大暴雨期间东亚大气低频振荡活动。从低频振荡特征看，江淮雨量和东亚风场中低频振荡现象是普遍存在的，风场的振荡周期具有显著的地域和频域分布特征。从低频波的传播看，这一梅雨过程的两个异常阶段（５月下半月和７月上半月），东亚风场低频波的水平传播方向发生了显著的变化。分析指出，低纬地区低频波虽有不同传播方向，但都将暖湿空气以低频形式输送到江淮以南，它与北侧的低频冷空气在江淮地区相互作用，从而导致该地区以低频形式出现的３场特大暴雨。

The activity of low frequency oscillation (LFO) in East Asia during the period of 1991 excessively heavy rain over Changjiang-Huaihe River Basin (Jianghuai) is specially studied in this paper. It is found that LFO widely exists in both the rainfall amount of Jianghuai and the wind field in East Asia. Dominant period of wind field shows obvious regional and frequency characteristics. Corresponding to the two anomaly periods of this Meiyu process (second half of May and first half of July), the propagation direction of LFO in East Asia has distinct seasonal variation. Further analysis suggests that although LFO may have different propagation direction in low latitudes, warm and moist airs with different sources can all be transported to south of Jianghuai in mode of LFO. They meet and interact with low frequency cold air from north, and lead to the three episodes of heavy rain in Jianghuai.