EAST ASIA SUMMER MONSOON ONSET DATE CALCULATED FROM OBSERVED, REANALYZED AND COMBINED DAILY RAINFALL

In this paper, the East Asia summer monsoon onset date lines in East China are calculated by the definition similar to the traditional one, with the ECMWF reanalyzed 850 hPa daily wind and observed, reana-lyzed and combined daily rainfall during 1980～1993. To make the onset date line as close as possible to the previous work, the earliest onset date limits have to be applied for the regions with different latitude and the daily mean datasets have to be smoothed by space before calculation, therefore their space-resolution is reduced to about 3 longitude ×1°latitude. The results show that the multiyear mean summer monsoon onset date lines are quite similar to each other. Compared with the one from the reanalysis, the 14-year average onset date line form combination is obviously improved in the southern Sichuan Basin and the correlation between observed and combined onset date is also slightly higher over the Huaihe valley and Northeast China. Since daily rainfall combination also improved the long term daily mean and standard deviation through the pentad CMAP, if no better daily dataset is available, such a kind of daily rainfall combination can be used to get reasonable result in the Indian monsoon region without sufficient observatories or over the North Pacific without any ground observation at all in future study.