Study On The Low-frequency Oscillation Features Of Precipitation In Summer And Its Relationship With Atmospheric Low-frequency Oscillation Over South China

753-station Daily and Monthly precipitation data from1961-2012provided by the National Meteorological Information Center and the NCEP/NCAR1961-2012daily data are used to investigate the low-frequency characteristics of the multi-year mean summer precipitation in South China and its relationships with low-frequency water vapor transport after1992and before firstly. Then nine flood years and nine drought years are selected to contrast the low-frequency characteristics of the summer precipitation. On this basis, the relationships of other elements of atmospheric circulation and the low-frequency precipitation are investigated and the sources of atmospheric low-frequency oscillation signal are revealed. The main results are as follows:(1) The summer precipitation in South China are tending to increase, and obviously more after1992(1993-2011, period Ⅱ) than before(1961-1992, period Ⅰ), especially in the most part of Guangxi, northern Guangdong and at the junction of Fujian and Jiangxi. Summer precipitation in South China shows significant10-20d oscillation, whereas more active in the period Ⅱ than in the period Ⅰ.(2) The zonal and meridional moisture flux are mainly controlled by10-20d、20-30d low-frequency oscillation in the summer. For the period Ⅰ, northwest anticyclonic water circulation, a pair of cyclonic and anticyclonic water circulation in the eastern part of the Indo-China Peninsula and the southern South China Sea are the main systems affecting10-20d summer rainfall. For the period Ⅱ, a pair of cyclonic and anticyclonic water circulation over the western North Pacific and in the east ocean of Indonesia respectively are the main systems influencing low frequency rainfall.(3) The significant period of oscillation of summer rainfall in southern drought years is10-20d low-frequency oscillation.10-20d low-frequency precipitation has the positive correlation with850hPa wind field, water vapor flux and500hPa potential vorticity (PV) which share the same cycle, it also has negative correlation with OLR in the same cycle.(4)10-20d low-frequency precipitation in the flood year is strongly influenced by the South China Sea cyclone, Northwest Pacific anticyclone, cyclone in the east of Indonesia ocean and Bay of Bengal and anticyclone in the east of the Philippines. Water vapor is mainly from Pacific Northwest, Southwest Pacific, island of Sumatra, Arabian Sea-the Bay of Bengal and east of Madagascar.10-20d cold air show the local variation without the dissemination of high and low potential vorticity cold air. The source10-20d cold air in the low troposphere is the South China Sea and the Western Pacific.(5) in the drought years,10-20d low-frequency precipitation is strongly influenced by the Western Pacific cyclone、cyclone in the ocean east of the Sea of Okhotsk、anticyclone in the southern Japan and the anticyclone in Arabian Sea-the Bay of Bengal. Water vapor is mainly from Pacific Northwest, Southwest Pacific and Arabian Sea-the Bay of Bengal.10-20d cold air show the local variation mainly. The source10-20d cold air in the low troposphere is Lake Baikal-Mongolia-North-Bohai Sea area and jianghuai-South China-South China Sea area.