The Variation Of Summer Monsoon Rain Belt In Flood Season And Its Monitoring In East China

The droughts and floods are closely linked in the conversion of summer monsoon circulation in flood season in east China,to prove the evolution of summer monsoon is conducive to further improving the short-time climate prediction and the monitoring application capabilities of summer monsoon precipitaton in flood season.By using the NCEP/NCAR reanalysis daily data, the daily rainfall data of600stations in China from1981to2010, based on the CVEOF(complex vector empirical orthogonal function), Composite analysis, Regression analysis and Power spectral analysis et al. statistical method, this study analyzed the characteristics of summer monsoon dominant mode and the intraseasonal Variation of Summer Monsoon Rain Belt in east China, revealed the interannual variation characteristics of east Asia summer monsoon and tried to use this method on the operational monitoring of summer monsoon rainfall. The main conclusions are as follows:(1)The first leading mode of summer monsoon is constituted by the real part and the imaginary part,its variance contribution is24.2%, their correlation coefficient is0.51and pasted0.01significant test, the large value areas of space amplitude are located in the low latitudes south35°N, the two high-value centers are located in Jiangnan region nearby26°N and the tropical western pacific ocean around Philippines nearby10°N,both centers are located in the subtropical and tropical regions and distributed to the longitude direction, therefore the first leading mode of summer monsoon prominently reflects the summer monsoon anomaly of the low latitude regions in tropics and subtropics. The variance contribution of the second leading mode of summer monsoon is14.2%, the large value areas of space amplitude are located in northern China and northeast China nearby44°N, the second leading mode of summer monsoon prominently reflected the summer monsoon anomaly of mid-altitudes, it is not only related to the low latitude subtropical monsoon system, but also affected by the high latitude circulation system, the correlation coefficient between real part and imaginary part is-0.01and did not pass the0.01significant test. Its phase is evenly distributed, different phase shows different distribution characteristics of droughts and floods. The real part corresponds to the "0°" phase and the imaginary part corresponds to the "90°" phase, the "180°" phase is contrary to "0°" phase and the "270°" phase is contrary to "90°" phase, they have mutual conversion relations. (2)The first leading mode prominently reflects the variation of summer monsoon rain belt in east China, and the anomalous center of southwest wind field has a sudden northward jump from the6th phase to the7th phase, it showing that the subtropical high eastward retreat and the anomalous of southwest winds northward jump from south China nearby20°N to Jiangnan and the middle-lower reaches of the Yangtze river nearby27°N after south China sea summer monsoon onset, the anomalous center of500hPa geopotential height fields and rain Belt northward beating, the plum rain begins. The anomalous center of southwest wind field has another northward jump from the7th phase to the8th phase, and the anomalous of southwest winds northward jumps from27°N to Jianghuai nearby32°N. From the7th phase to the8th phase, the anomalous center of southwest wind northward jumps from32°N to37°N, the rain belt moving northward and rainy season of north China begins.(3) The correlation coefficients of the real part and the imaginary part are0.75and0.52respectively between EASMI, both passed the test of significance, it prominently reflects the interannual variability of EASMI from the point of dynamic, The time coefficient of the first leading mode can be used as summer monsoon intensity index. The Summer monsoon is stronger in these years:1982、1985、1986、1990、1994、2001、2004and2009,the precipitation in the middle and lower reaches of the Yangtze River and Jianghuai regions is anomaly less than normal in stronger years. The summer monsoon is weaker in these years:1983、1988、1993、1995、1998、2010,the precipitation in the middle and lower reaches of the Yangtze River and Jianghuai regions is anomaly higher than normal in weaker years. Power spectral analysis shows that the first two modes have2-3years interannual oscillation, which passes the significant test at a level of0.95confidence, thus it reflects the possible links between the summer monsoon and ENSO from the other side.(4)This study obtained the phase and amplitude of the leading summer monsoon by using CVEOF, the results are reasonable, this method can be further improved and we can try to translate it into operational monitoring applications.