Research On Meiyu Division In Multi-Modals And The Characteristic Of Atmospheric Circulation In Abnormal Entering Meiyu Years

Meiyu not only exist in the Yangtze River basin in China, but also appear in the Huaihe River basin and the south of Yangtze River. By using NCEP/NCAR reanalysis data and observational data at 721 stations given by National Meteorological Center, applying some statistical methods such as rotated empirical orthogonal function (REOF), wavelet analysis, composite analysis and correlation analysis, characteristics of Multi-Modals of meiyu are researched. The main conclusions are as follows:By using the REOF analysis of the averaged June to July rainfall (the meiyu amount) during the years from 1961 to 2009, it is founded that there are 4 models in the meiyu areas of eastern China, which are defined as the Yangtze River pattern (YP), the South pattern (SP), the Yangtze River-Huaihe Rive pattern (YHP) and the East pattern (EP). Interannual and interdecadal variations are obvious in all models. Periodic oscillations are also significant.The demarcation of meiyu period is made in each pattern, mainly based on the pentad precipitation. Other elements are also considered such as the latitude of the ridge line of SH and SAH, temperature, etc. A new climatic averaged meiyu area is put forward.It is founded that all of the parameters of SAH exist the remarkably interdecadal variations in summer, the same as the correlation with the precipitation during meiyu period. The indices of the area, intensity and the east ridge point longitude position of SAH have a significant positive correlation with the meiyu amount of YHP. There is a negative correlation between the latitude of the ridge line of SAH and the rainfall of SP.