A Study On Characteristics Of The First Soaking Rain In Northeast China And Its Influencing Factors

Based on the precipitation data in April and May for the period 1958-2012 from 101 meteorological stations in Northeast China, the observed data from 96 meteorological stations in Northwest China and other reanalysis data. Using EOF decomposition, correlation analysis, synthetic analysis and other methods, the study is performed of the first soaking rain date as well as its relation with the soaking rainfall and the total rainfall from April to May, the differences of soaking rain circulation in sooner and later years. In addition, responses of the soaking rain date to the surface heat source over the Tibetan Plateau, the surface heating fields in Northwest China, and Siberia high pressure strength are also discussed. At last, we analyze 74 circulation indices from National Climate Center, and establish a forecast equation about the date of soaking rain.The results suggest that soaking rain date advances gradually from southeast to northwest, the amount of rain decreases gradually from south to north. The place where the soaking rainfall is smaller(larger) and the total rainfall is larger(smaller). If the occurrence of soaking rain early, the Eurasian continent presents a trough of two ridges, the Northeast China is covered with a large range of trough area, there is a strong vertical upward movement in the area, air flow can be increased from a low level to more than 200hPa, the Northeast is covered with strong water vapor convergence; if the occurrence of soaking rain late, the Northeast China is controlled by high pressure ridge, air flow decreases, the Northeast is covered with water vapor divergence. The soaking rainfall is also related with sea surface temperature adjacent China(20°N～40°N,110°E～140°E):If the sea surface temperature high(low), the first soaking rain date is early(late).Besides, the correlation between the surface heat source over the Tibetan Plateau in April and the soaking rain date is negative, which means when the surface heat source in April gets enhanced, cold air from the north is strengthened, and water vapor transport is abundant, making the soaking rain date in Northeast China comes early(late). From the point of forecast view, the intensity of surface heating fields in Northwest China enhanced(weaken), Siberia high pressure strength enhanced(weaken), the soaking rain date in Northeast China comes early(late).