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

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.