Definition For North Huaihe River Rainy Season And Its Climatic Characteristics

In this paper, the data used are as follows:the summer daily rainfall data from 1961 to 2009 based on 278 meteorological observations in East China. The NCEP/NCAR daily means reanalysis data and SST data are applied in atmospheric circulation analysis. The 74 atmospheric circulation index offered from National Climate Center are also employed in this article. Common statistic functions such as circulation composite analysis, liner trend analysis, abrupt change testing, Wavelet analysis, SVD, EOF, REOF as well as HYSPLIT Model, etc. are applied in this article. A new definition for North Huaihe River Rainy Season(NHRS) is presented in this article. By synthetically analyzing the spatial-time distribution characteristics of NHRS and ocean-atmosphere circulation characteristics influencing NHRS, main conclusions are obtained as followings:1) The rainfalls in East China present clearly regional distributions characteristics. Compared comprehensively, in the later June every year, after the beginning of Jianghuai Meiyu(JHMY), and before the beginning the North China Rainy Season, a distinguishing continuous rainfall occurs in the northern areas of Huaihe Region in East China can be called as NHRS with its normal location from 33°N to 37°N, and its duration between later June and most July.2) The subtropical high ridge axis on 500hPa and daily precipitation are applied in defining the NHRS. The new definition refers less meteorological elements, and is profitably to estimate the beginning and ending dates in the practical operation. The new definition can be used on more extensive areas. Furthermore, two periods of NHRS can be easily classified by the new definition so as to be used to synoptic and climate practical operation.3) The average date of beginning day in NHRS is June 25th, and the ending day is July 16th. The mean precipitation of NHRS is 182mm, and shows obvious inter-annual and decadal variation. The spatial distribution of average precipitation presents more in the south than in the north, and the difference is obvious. Moreover, JHMY shows certain relationship with NHRS, characterized by the beginning of JHMY can monitor and forecast NHRS to some extent.4) As the strength and variation of various vapor passage are totally different, they play different role in precipitation of NHRS, among which the influence of vapors from the Bangladesh Bay, the South China Sea and the West Pacific are distinguishing. By analyzing the 264hr vapor passage grid of NHRS with HYSPLIT4.9 Model, different characters of the vapor transportation from the Bangladesh Bay, the South China Sea and Indian Ocean revealed the causations for the positive and negative years.5) The impact factors for NHRS includes:the location and strength of South Asian high; the location and strength of the blocking high, and trough exists in East Asia, the activity of East Asian Summer monsoon, etc. Besides, by studing the characteristics of impact factors above, one climatic forecasting model of the beginning date and precipitation for NHRS is established. Moreover, The Pacific SST and ENSO have close relationship with NHRS.