The Extreme Precipitation Events In Eastern China And The Possible Reason Analysis During Boreal Summer

In this paper, using 438 stations daily precipitation data from 1961 to 2014 in eastern China, based on the daily and monthly NCEP/NCAR reanalysis data,calculating the extreme precipitation indices and the extreme precipitation events,according to the relevant statistical analysis, synthesis analysis, the variation characteristics of extreme precipitation events in China during the last 54 years are discussed. The anomalous circulations for different extreme precipitation events in summer from the perspective of atmosphere dynamics were investigated.Furthermore, we focus on the possible linkage between the vertically integrated atmospheric heat source over the Tibetan Plateau and the extreme precipitation. Our main results are as follows:The long-term variation trends of the 8 extreme precipitation indices over eastern China show that most of extreme precipitation indices in the Northern China are decreasing, which indicate that the extreme precipitation events decreased in North China, in the Yangtze River region, in addition to the continuous dry days index(CDD), the other extreme precipitation indices are increased, the main indices of extreme precipitation are increased in southeast coastal areas of China as well as in most areas of Southern China. That is to say the extreme precipitation events are more likely to occur in these regions. The intensity and frequency of extreme precipitation in North China showed a decreasing trend in temporal and spatial dimensions, while which showed a consistent increasing trend over the middle and lower reaches of the Yangtze River .In the middle and lower reaches of the Yangtze River, when the frequency of extreme precipitation increased, the anomaly field based on 850hPa wind field and the water vapor flux showed that the East Asian summer monsoon (EASM) is weaker,both strength the water vapor transport to the middle and lower reaches of Yangtze river, 500hPa a blocking high pattern persists over Okhotsk Sea, which is conductive to the cold air moving southward. East Asian subtropical westerly jet with the anomalous southward movement on 200hPa, the westerly wind anomalies in the south of 30°N benefit for divergence, the wave activity fluxes are favorable to generating and maintaining of the wave perturbation in this region. In North China,when the frequency of extreme precipitation increased, the anomaly field based on 850hPa wind field and the water vapor flux showed that the East Asian summer monsoon (EASM) is stronger, both of which strength the water vapor transport to North China, the positive anomaly over the sea of Japan and the negative anomalies in Mongolia, Baikal and their vicinity on 500hPa, East Asian subtropical westerly jet with the anomalous northward movement on 200hPa, the wave activity fluxes are also favorable to generating and maintaining of the wave perturbation in this region.There is a close relationship between the vertically integrated atmospheric heat source over the Tibetan Plateau and the extreme precipitation in Eastern China in summer, especially in parts of middle and lower reaches of the Yangtze River. When the intensity of summer atmosphere heat source over the Tibetan Plateau is stronger,the extreme precipitation is more than normal in parts of middle and lower reaches of the Yangtze river. The area occupied by South Asian High(SAH) is larger, and the100-hPa geopotential height over the SAH center is higher than that in normal years, the east edge of the SAH expands eastward during strong SAH years.The ridge position of Western Pacific subtropical high lean to south, This circulation is propitious to making for the more extreme precipitation in eastern China (Yangtze River). Furthermore, the upward motion over the Tibetan Plateau is stronger, the water vapor transport and convergent upward velocity are strengthened, vice versa.