The Temporal And Spatial Features Of Summer Rainfall And Extreme Summer Precipitation Process In Northeast China And Its Diagnosis Analysis

Summer precipitation in Northeast China ranging from 1960a to 2000a and NCEP reanalysis data is applied to study the temporal and spatial features of summer rainfall and extreme precipitation in Northeast China. The results show:1 Summer rainfall in Northeast China exhibits upward trend with the cycle variation of 14 years and 2 to 4 years. Two abrupt changes occurs in summer rainfall with its happening time on 1964 and 1988/89.2 The intraseasonal variation features of summer precipitation in Northeast China are that the 24 percent of summer precipitation concentrate on late-July and first dek of August, i.e. the 12th, 13th and 14th pen of summertime. The summer precipitation in Northeast China mainly distribute in Inner-mogolio from Jjune to the middle of July and Liaoning from the end of July to the middle of Auguest.3 The change of summer rainfall in Northeast China falls into 5 types: The southeast of Inner-mogolio type, The east of Liaoning type, The northeast of Heilongjiang type, The west of Heilongjiang type and The centra] of Northeast China type. Different areas present different variation tendency of summer rainfall, among which the rainfall significantly decreases in the east of Liaoning and increases in southeast of Inner-mogolio. Meanwhile, the precipitation of different areas exhibits different cycle periods and different time of abrupt change. In the long-term variation trend of heavy rain days and its intensity, most areas present increase tendency with the exception of the area of Liaoning. There are positive correlation between heavy rain days and summer precipitation.4, The summer rainfall anomaly in Northeast China bears close correlation with the atmospheric circulation backgroud. While cold air in middle and high levels of troposphere is active in wet year with the positive anomalies over high-latitude and polar area, the active longwave ridge, the anomalous long-wave ridge in Northeast China and Inner-mogolia as well as the northward and eastward of the polar vortex, the contrary is in the dry year in Northeast China.5 The positive correlation exists between the summer rainfall in Northeast China and NINO3 SST. The atmospheric circulation of the wet year deviate from ENSO year to NO-ENSO year. In ENSO year, the Subtropical High is strong with the deepening of trough over south of Baikal Lake while in NO-ENSO year, the Subtropical High is weak with the high incidence of typhoons over northwest of Pacific and South China Sea.6, The intraseasonal discrepancy exists in the temporal distribution of extreme rainfall in Northeast China. While extreme rainfall appears in August in the east of Liaoning and the northeast of Heilongjiang, so does June in other three areas. Moreover, the weatherbackgrounds under which the extreme precipitation occurs are also different. While theprecipitation of southeast of Inner-mogolio is attributed as the strong convective precipitation,the rainfall of Liaoning and northeast of Heilongjiang is induced by Subtropical High andwesterly trough, and that of west of Heilongjiang is influenced directly by vortex in upperair.