Intraseasonal Variation Of Midsummer Precipitation Anomaly In South China And Its Related Causes

Based on monthly mean precipitation data from CRU, CMAP,PREC/L,CN05.1,NCEP/ NCAR reanalysis and 160 Chinese meteorological stations, the intraseasonal variation of the midsummer precipitation in South China and related atmospheric circulations during recent 50 years are investigated by using multi-variables statistic methods, including empirical orthogonal function (EOF) decomposition,season-reliant EOF (SEOF), moving average, spatial correlation, regression analysis and composite analysis. Results show that:(1) The precipitation anomalies(PA) in both July and August exhibit consistent spatial variations. Further analysis of the time series and regional mean PA shows that regional mean PA can represent the basic characteristics of South China precipitation, and if a certain PA mode is observed in July, the possibility of observing the same (opposite) sign in August is approximately 47% (53%)(2)There are evident intraseasonal variations in the midsummer precipitation over South China. During 1963?1993,there is an out-of-phase evolution of precipitation anomaly from July to August,implying more (less) rain in July usually corresponds to less (more) rainfall in August. However, there is an in-phase relationship between July and August precipitation during 1994?2015, i.e., more/less August rainfall is generally accompanied by more/less July precipitation.(3)Analysis of related atmospheric circulation anomaly suggests that the anomalous atmospheric teleconnection patterns plays dominant roles on the two intraseasonal modes of the rainfall. For in-phase case, the anomalous circulation of the middle troposphere in July is mainly featured by typical Eurasian (EU) and East Asian/Pacific (EAP) teleconnection patterns, while it is related to the EU and Pacific/North American (PNA) teleconnection patterns in August. For out-of-phase case, the spatial pattern of circulation anomaly is similar to the North American East/West (NAEW) teleconnection pattern in July and the EAP teleconnection pattern in August.(4)The variation of the western Pacific subtropical high (WPSH) in July and August is closely related to the intraseasonal variation. In out-of-phase years, the East-West position of the WPSH changes evidently from July to August, while no significant change has been detected for in-phase years.(5) Analysis of related sea surface temperature (SST) anomaly suggests that for in-phase case, when SST of the northern and southern North Atlantic Ocean,remained to be low (high) during decaying (developing) La Nina phase and developing (decaying) El Nino phase from January to August , there is more (less)rain both in July and in August. For out-phase case, when SST of the northern and southern North Atlantic Ocean remained to be high (low),and that of Kuroshio and extended sea surface remained to be low (high) during developing (decaying) El Nino phase from January to August, and there is more (less) rain in July and less(more) rain in August.