The Relationship Between Low Frequency Oscillation over Asia Monsoon Region and Continuous Heavy Rain in the Lower Reaches of Yangtze River Valley

By using the principal component analysis and the power spectral analysis with nonintegral waves, the characteristics of the spatial distribution and low frequency oscillation for 500 hPa circulation over Asia monsoon region during the early summer in 1991 are investigated. The results show that the first five major spatial patterns from the principal component analysis respond to the influence of different monsoon systems, respectively, and time coefficients have the remarkable periods of 12―22, 28―31, 43―65 days. The variation of oscillations is related to the heavy rain in the lower reaches of Yangtze River valley. It is important to the occurrence of continuous heavy rain that interactions between the low frequency waves which are forced by the diabatic heating anomalies and the continent-ocean heat contrast at the low latitude in Asia will lead to the anomalies of energy dispersions toward extratropical atmosphere