Analysis of the Leading Modes of Autumn Precipitation over the Yangtze River Basin

Based on daily precipitation data from 109 stations in the Yangtze River Basin (YRB) over the past 36 years (1980`-2015), the Empirical Orthogonal Function (EOF) is employed to analyze changes in autumn precipitation. We used the monthly mean re-analysis datasets of atmospheric circulation and sea surface temperature (SST) to investigate the possible causes of the two leading modes, based on which the predictive equations were constructed and tested. The results of the EOF analysis show that the variance contribution of the first mode is 31.07%, and the spatial distribution shows a uniform variation over the whole region. The variance contribution of the second mode is 15.02%, and the spatial distribution displays a north-south dipole pattern in the YRB. The leading mode shows a dominant interannual variation, which is mainly due to the West Pacific subtropical high and anticyclones over the Philippine islands. The SST field corresponds to the positive phase of the eastern Pacific El Nino and the tropical Indian Ocean dipole. The second mode may be related to the Indian Ocean-East Asian teleconnection and early withdrawal of the summer monsoon. The SST field corresponds to a weaker central Pacific El Nino. Through a stepwise regression analysis, SST anomalies in some areas during summer show a good predictive effect on the autumn precipitation mode in the YRB region.