Variations And The Extremes Of Regional Rainfall In East China During Boreal Summer:Phenomena And Mechanisms

Using the daily data of precipitation from China Meteorological Administration, and the Meteorological Information Combined Analysis and Process System2.0(MICAPS2.0), and the NCEP/NCAR reanalysis as well as the Sea Surface Temperature (SST) data from the Meteorological Office Hadley Centre, the regional patterns of summer precipitation of China especially the rainfall over regions east of105°E have been studied. Several regions have been identified as per the interannual variations of summer rainfall over China. Based on these region identifications, the anomalous precipitation and the regional extreme events as well as the impact facts and mechanism of these events have been discussed. Main results are summerized as follows:(1) China summer rainfall and its interannual (interdecadal) variability are uneven in spatial. They are rich in southeastern part of China and deficient in northwestern, showing a decreasing tendency from southeastern to northwestern. Twenty one subregions have been designated as per the variability of summer rainfall over China, and these21regions cover most territory of China except for some parts of west and southwest China. Except for the middle and lower reaches of the Yangtze River (MLRYR) and Hetao Region, the precipitations in other19regions do not have close correlation with each other. The features of summer rainfall in different regions and their periods are notable different; and the precipitation variations are found to be significantly regional. The sea surface temperature anomalous and atmospheric teleconnections related with the rainfall anomalous of each region are also different.(2) Four regions (Guangdong-Guangxi, the middle and lower reaches of Yangtze River, Qinlin Mountains to Yellow River-Huaihe River plain, and the middle and lower reaches of Yellow River) are found arounded110°E from south to north, where the precipitation variations are significantly different in temporal and spatial during recent50years. The source of moisture transportation, the atmospheric teleconnections, as well as the related SST features are also remarkably different from one region to another.(3) Summer rainfall and its interannual variability in MLRYR are rich, and deficit in HTR on the interannual time scale. Summer precipitation in the middle and lower reaches of Yangtze River (MLRYR) and Hetao Region (HTR) oscillate in out-of-phase on the interannual time scale. The related moisture transportation is mainly from northwest Pacific. This out-of-phase oscillation has remarkable correlation with North Atlantic Oscillation (NAO). The linkage between out-of-phase oscillation and the NAO is possibly connected with the circumglobal teleconnection (CGT).(4) Northeast China (NEC) suffered an extreme flood event in the summer of2013. The largest values regions are found in the Northern of NEC (NNEC) and Southern of NEC (SNEC). Statistical results show that diffenent atmospheric circulation and moisture transportation paths caused the rainfall greater than normal in those two regions. Water vapour transported from tropical central Pacific and mid-latitude westerlies caused the precipitation over the NNEC and SNEC are greater than normal in JJA (June-July-August) of2013. The anomalous summer rainfall over the whole NEC attributed to the combined influences of the Northern of NEC (NNEC) and Southern of NEC (SNEC). The Eurasia-Pacific (EUP) teleconnection and thermal forcing in Maritime Continent region lead to the precipitation over NNEC greater than normal; CGT teleconnection, East Asian monsoon, the sea surface temperature anomalous over tropical eastern Pacific and northern Atlantic combined influence the rainfall of SNEC greater than normal.(5) The middle and lower reaches of Yangtze River (MLRYR) experienced two extremely drought events during summer of1985and January to May (JFMAM) of2011. The two extreme drought events were found to be related to some different factors. The summer extreme drought event in1985was significant affected by East Asia Pacific (EAP)/Pacific-Japan (PJ) teleconnection. However, the extreme drought event in JFMAM of2011was notable influenced by the quasi-stationary wave train which originating from North Atlantic in Midhigh latitudes. Both the two extreme drought events were closely connected with the thermal forcing in Maritime Continent.