The Structure For The North Boundary Of Subtropical Summer Monsoon In East Asian And Its Impact On Summer Rain In Yellow River Basin

Based on the daily precipitation data of661stations of China and NCEP/NCAR daily reanalysis data during1951to2009, the inter-annual, decadal variations and structural features on the north boundary of the East Asian Subtropical Summer Monsoon were firstly analyzed. The results show that:the north boundary of subtropical Summer Monsoon in East Asian is roughly in northeast-southwest direction, the southern edge of the north boundary is located roughly36°N at110°E, the northern edge of the north boundary is located approximately41°N. There is a good negative correlation between the boundary width and the southern edge of the boundary, the boundary width has a wider trend year by year. The north boundary has significant2a,3a,9a periodic oscillations. The Summer Monsoon began to affect the north boundary at July28, and at Sep.21to leave. It is at110°E that the north boundary has the maximum south wind component, also the jet center is located over the edge at200hPa, the west wind on the southern edge of the north boundary is less than that on the northern edge with the same level. Under600hPa is the south wind, and above600hPa is the north wind, south wind component on southern edge of the north boundary is greater than that in the northern edge. The water vapor content can be reach400hPa, the contours about relative humidity is most intensive at the boundary. Compared with the southerly years, the date of summer monsoon arriving at the boundary is earlier and leaving later in the northerly years, and the jet center located more north and stronger, the humidity on low levels is also stronger, so is the ascending motion.Then the precipitation characteristic of the Yellow River Basin has been analyzed by using the monthly precipitation data of92meteorological stations in the Yellow River Basin from1959to2008. The result shows that the precipitation is more in the southeast and less in northwest as a whole, and so pluvial present the trend of the northeast-southwest. The precipitation of the Yellow River Basin has significant2～3a,8～9a periodic oscillations. The spatial anomaly features of summer precipitation in the Yellow River Basin are mainly three kinds:wet or dry in all area pattern, wet (or dry) in north and dry (or wet) in south pattern, wet (or dry) in east and dry (or wet) in west pattern. The cumulative variance of the three kinds is42%. The Yellow River Basin summer rainfall showed a gradual upward trend in two period:among the1970s, later1980s to1990s, and summer rainfall in the Yellow River Basin in the late1960s, early1980s and late1990s show a downward trend.There is a significant positive correlation between the north boundary of the East Asian subtropical summer monsoon and summer rainfall in the Yellow River Basin, when the north boundary of the East Asian subtropical summer monsoon lies northern, there are more rainfall in the Yellow River Basin, on the contrary, when the north boundary of the East Asian subtropical summer monsoon lies southern, there are less rainfall in the Yellow River Basin. When anomalies north of the East Asian subtropical westerly jet center, more summer rainfall in the upper reaches of the Yellow River Basin and less in the lower reaches of the Yellow River Basin, when the anomalies south of the East Asian subtropical westerly jet center, the summer precipitation in the upstream region of the Yellow River Basin less than normal and the downstream region is above normal. Anomalies east of the East Asian subtropical westerly jet center, the summer rainfall of the Yellow River Basin in upstream region above normal and less in the middle and lower reaches of the Yellow River, when anomalies west of the East Asian subtropical westerly jet center, the middle and lower reaches of the Yellow River basin precipitation above normal, the upper reaches of the Yellow River basin rainfall less than normal.When summer precipitation anomalies of the Yellow River Basin, there are obvious differences of the atmospheric circulation in East Asia, in the years with abnormally more summer rainfall in the Yellow River Basin, the intensity of South Asia High at100hPa is stronger than normal, and the location is in north-east, the intensity of EASWJ center at200hPa westerly also on the strong side with a northerly location, the Western Pacific subtropical high at500hPa lies northwest, the south wind at850hPa on the strong side too, the water vapor transport is stronger over the eastern part of China, the moisture convergence in the Yellow River Basin is the strong side.