Variation Characteristics Of Extreme Precipitation Over The East Of China And The Reason Analysis

By using the daily rain data of 392 stations of the Eastern China, the characteristics of extreme precipitation of the Eastern China during the recent 50 years are analyzed firstly. Then the response characteristics of the extreme rainfall over eastern China in different seasons to the ENSO are studied. In addition we utilize the theory of moist potential vorticity(MPV) to investigate the possible reason. At last, by dividing the research time into 1948-1976 and 1977-2008, the differences of moist potential vorticity(MPV) and the atmospheric stability of the two periods are focusly discussed based on the NECP/NCAR reanalyzed data. The mositure flux and the vertical motion are also analyzed. From the point of the cooling of the air in the middle and upper troposphere, we inquire into the reasons of the differences of the atmospheric stability during the two periods. The main results are as follows:1)The extreme precipitation over the Eastern China exhibits more along the southeast and less in northwest inland, but different in each decade:The count,its percentage of the total rain,the frequency and the intensity of the extreme precipitation all decreased in North China while increased in South China. The four factors of the North China and lower reaches of the Yangtze River take a change which is similar to the mutation form the late 1970s to the early 1980s and the precipitation pattern changes in 1976.That means the rainfall over the North China transform into dry state while the South China coverts into wet state;2)The extreme rainfall differs significantly over the east area of the Northern China in the warm and cold years. In the spring and summer of the following year of El Nino, it has nearly the same distribution that the north exhibits more and the south exhibits a complex distribution that there is a great value over the south area of the Yangtze River valley; In the autumn of the following year, construct to the spring and the summer. The big value is main over the northern region; in the winter, it mainly has less. However, it presents an adverse distribution pattern in the following year of La Nina; The corresponding MPV can well reflect the atmospheric stability of the north area, especially Northern China but not perfectly in the Low-latitude region; 3)The MPV exhibits a reduction in the North China and a growth in the South China. The convective stability changes significantly in the two stages and shows less in the south and more in the north in the next stage on the lower level. That is to say that the south area tends to be convectively unstable and the North China tends to be convectively stable; The baroclinic stability of the middle latitude shows minus departure on the lower level in the former stage and reversedly in the latter stage. The baroclinic stability of the whole east area takes on a increasing tendency; On the middle level it shows less in the south and more in the north in the next stage That means that the south area tends to be baroclinicly unstable and the North China tends to be baroclinicly stable. The variation of the atmospheric property is a main reason for the change trend of the extreme precipitation over Eastern China;4)The moisture reaching the North China deceased remarkably after 1976.The low latitude changes from downward movement to upward movement and the high latitude changes contrarily; The temperature shows minus after 1976 on the 300hPa level over the high latitudes,which leads to the difference of the thermal properties and then affects the convective stability; Meanwhile the temperature decreasing makes the west wind increase in the south and decrease in the north respectively and the baroclinic stability weakens and strengthens accordingly.