Characteristics of Multi-patterns of Precipitation over the Yangtze-Huaihe Basins During Meiyu Season in Recent 30 Years

The spatial patterns of precipitation during Meiyu season (June—July) over the Yangtze-Huaihe Basins are analyzed under different distributions of surface stations. 424 stations to the east of 110°E are chosen for the rotated empirical orthogonal function (REOF) analysis during 1979—2010. Then, three precipitation patterns are obtained, i.e., the south pattern (SP), the Yangtze pattern (YP), and the Yangtze-Huaihe pattern (YHP).On the inter-annual time scale, it's found that the out-of-phase relationship displays more remarkably between the rainfall of SP and YHP in recent 30 years. However, the precipitation of YP shows no significant relationship with that of SP and YHP, revealing as more independent precipitation pattern. In addition, the YP has the most climatological precipitation, and shows the largest variability. While on the inter-decadal time scale, the YP precipitation is identical with that of SP. Nevertheless, the precipitation of YHP exhibits out-of-phase relationship with the YP and SP, especially since the early 1990s. There are obvious inter-decadal changes in the early 1990s and early 2000s in all spatial precipitation patterns during Meiyu season. But different from the previous years, by 2010, the YP and SP precipitation has increased a little but the YHP precipitation has decreased, suggesting a new inter-decadal variation.The regression using ERA-Interim reanalysis data indicates that corresponding to the anomalous precipitation, the intensities and positions of sub-systems of East Asian summer monsoon circulations, such as the south Asia high (SAH), the western Pacific subtropical high (SH) and the subtropical upper jet stream (JS), have notable differences which also exist in the monsoon meridional circulations and water vapor transport flux. Specifically, when the YP precipitation is in the flood years, the intensities of the SAH and SH enhance apparently. When the YHP precipitation is strong, the SAH and JS locate east, meanwhile, the geopotential height over Aleutian Islands maintain positive anomalies. The positive phase of the East Asia-Pacific teleconnection pattern and the negative phase of the Eurasian teleconnection pattern make it difficult for the SH to shift northward and confine it to a southern position, which in turn enhance the SP rainfall remarkably. Additionally, it is found that the SH, the monsoon meridional circulations, together with the vertically integrated water vapor transport flux stay successively in northern places, accompanying by a northerly rainfall pattern. Further analyses on sea surface temperature (SST) present that the previous SST of the east Pacific Ocean of the equator shows significant relationship with the precipitation of YP and SP. The cool SST of the western Pacific warm pool and warm SST in Chinese coasts and the Kuroshio area restrain the precipitation in the SP. But there is no distinct correlation between the precipitation of YHP and the tropical SST in the prior period, which implies that the tropical SST plays no key role in the YHP precipitation since 1979.