In the past research, there are many studies on the characteristics of the summer precipitation in Sichuan-Chongqing basin, but most of them are separately discussed in terms of its annual or inter annual variation characteristics and its possible mechanism. The analysis of the characteristics of the seasonal variation is relatively less. Therefore, in this paper the characteristics of the seasonal interannual and decadal variation will be studied systematically and deeply from different time scales. The daily precipitation data from 1961 to 2010 of 24 meteorological stations are used in this paper. Use the same period monthly mean 500 hPa, 100 hPa height field and 1000~300 hPa zonal wind and humidity field reanalysis data. Two methods are used in this article. MTM-SVD method is a multivariable frequency domain decomposition technique proposed by Park and Mann. The empirical orthogonal function expansion technique was introduced into the study of atmospheric science by Lorenz in the middle of 1950 s. The results show that the main mode of summer precipitation in Sichuan-Chongqing Basin is the East-west reverse distribution pattern. MTM-SVD analysis points out that the seasonal changes of summer rainfall at Sichuan-Chongqing Basin mainly reflected the oscillation of Quasi-33 day. The seasonal typical cycle performed the evolution between the distribution of east-west reverse and the north-south. Its interannual variation mainly showed Quasi-2 years cycle, which spatial distribution is consistent with that primary mode. In the aspects of decadal variations, the summer precipitation has decreasing trend in the western basin but growing trend in the eastern basin. The results of sliding t test indicated that the summer rainfall appeared two distinct mutations in 1979 and 1987. Synthetic analysis shows that corresponding to the abnormally northeastward South Asia high (SAH), the West Pacific subtropical high (WPSH) inclines to more northward, while the warm-humid air from the Bay of Bengal is blocked in the west basin which leading to more precipitation in west basin than the east basin. The southwestward SAH and the southward WPSH always accompanies more rainfall in the east basin than the west. In this paper, the fact of the multi scale variation of the precipitation in the basin is analyzed, and the general circulation background of the typical year is given too. The impact factors for different time scale characteristics are not the same. The characteristics of precipitation intraseasonal oscillation signal may affected by the plateau vortex and MJO. Interannual time scale signal is mainly affected by the Indian Ocean dipole, the thermal status of Tibetan Plateau external forcing, decadal scale change should be considering the factor of solar activities, etc., which are worth further study.
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