| By using 1951-2008 NCEP/NCAR monthly reanalysis data, the Japan Meteorological Agency JRA-25 data and station data of precipitation in China, the probability distributions of atmospheric water vapor content of the Haihe River Basin and the water vapor flux decadal variations, spatial distribution, as well as large-scale circulation system—the East Asian summer monsoon, the West Pacific subtropical high and mid-latitude westerly systems in Haihe River Basin Water Vapor content are investigated by methods of MK, EOF, SVD statistical diagnosis. Some results are received as follows:(1)Water vapor content of the Haihe River Basin and changes in precipitation characteristics consistent, showing mid 1950s to 1960s above normal, it from mid-60s began to decrease, the 1980s and 2000s below normal. Water vapor content and precipitation significant reduction in mutations of water vapor content and precipitation occurred at about 1970 and 1976.(2)Water vapor flux field can reflect the characteristics of the circulation patterns of Haihe River basin five circulation patterns. Haihe River Basin water vapor flux at 850hPa and the surface wind field is consistent characteristics, are able to reflect the circulation pattern of the circulation features, However, the size of the water vapor flux is not completely consistent.850hPa, the south wind type is the largest, followed by cyclonic type, east wind and west wind type, anti-cyclonic circulation under the minimum. Surface, east wind type is the largest, followed by the south wind type and cyclonic type, west wind type and anti-cyclonic circulation are minimum. Between 850hPa and surface water vapor flux is mainly wind-type, this difference was mainly due to thermal differences between land and sea surface by the impact of large, obvious features in the east wind type, by the thermal difference between land and sea formed by the strengthening wind, so largest surface water vapor flux.(3)The water vapor of the Bay of Bengal monsoon through the Indochina Peninsula to reach the South China Sea, then turned into a southwest flow, arrived Haihe River Basin; mid-latitude westerly water vapor transport from west to east effects; West Pacific subtropical Southwest side air into the western Pacific and South China Sea water vapor through the southeast coast, transported to the Haihe River Basin.(4) When the East Asian summer monsoon is relatively strong, the East Asian summer monsoon tend to be more water vapor to northern regions; and when the East Asian summer monsoon is weak, the South water vapor can not transport to the Haihe River, the Haihe River Basin of atmospheric water vapor content is low. When the Western Pacific subtropical high ridge is norther, area is small, west ridge point is easter, the deputy high on the southwest side of the air can affect the southeast area of northern China, the Haihe River Basin water vapor content is larger; when the West Pacific subtropical high ridge is souther, area is large, west ridge points is wester, the subtropical high on the southwest side of the southeast flow is often affected the southern region of China, the Haihe River Basin water vapor with smaller side, mid-latitude westerly water vapor t strength which is too large, when it is more south and east, it greatly influenced the Haihe River valley in China, the atmospheric water vapor of Haihe River Basin content is larger; mid-latitude westerly water vapor strength which is too small, when it is more north and west, it little influenced the Haihe River Basin, the atmospheric water vapor of Haihe River Basin content is smaller. Impact of these three systems use the 8 factor regression index as a regression analysis, we found a very good representative to atmospheric water vapor content of the Haihe River Basin.
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