Temporal And Spatial Variations Of Water Vapor Content Over North China

Based on 1979-2008 sounding data from 12 sounding stations, contemporaneous precipitation observations from 50 stations and NCEP/NCAR reanalysis data and 1979-2001 ERA-40 reanalysis data in North China, the variation characteristic and correlation of precipitation and water vapor content in North China were studied by means of many statistical methods, and then the main climatic factors affecting water vapor content were analyzed, as well as the applicability of reanalysis data in North China. The main conclusions were as follows:(1) Precipitation in North China decreased gradually from southeast coast to northwest inland area, with greater spatial difference. The precipitation went down in most regions, and climate arid became more and more obvious. Moreover, precipitation had obvious annual variation, and climate became dry suddenly at the end of 1990s.(2) Atmospheric water vapor content in North China also showed decrease trend from southeast coast to northwest inland area, with greater spatial difference. Water vapor content went down in western margin and part of eastern region and went up in other region, especially in middle region with obvious increase trend. The water vapor content in four seasons all showed slight increasing trend in recent 30 years, and water vapor content increased greatly after the middle of 1980s except spring, in addition, water vapor content in summer had the variation period of 3～4 years and 8 years, while variation period was 4 years,6 years and 12～14 years in other seasons, respectively.(3) In recent 30 years, precipitation efficiency in North China showed fluctuating decrease trend and was lower in four seasons. The first mode of SVD components the intimidate relationship between water vapor content and precipitation in North China,that is to say,when water vapor content is more (less) than normal, precipitation in most area of North China is more (less) than normal, but it is different in different seasons.(4) Abnormal water vapor content was related to atmospheric circulation, and there was (no) obvious water vapor convergence to North China from South China Sea to Western Pacific, while there was (no) water vapor transport to North China in westerly belt in middle latitude during the year with more (less) water vapor, and subtropical high moved more westward and became more stronger in the year with more water vapor content at 500 hPa. In addition, abnormal water vapor had certain relation with land surface temperature, namely the higher the land surface temperature, the more the atmospheric water vapor content, and vice versa.(5) The spatial distribution of annual average water vapor over North China based on NCEP/NCAR and ERA-40 reanalysis data was relatively similar with sounding data in value and distribution pattern.The results of annual average water vapor over North China based on NCEP/NCAR and ERA-40 reanalysis data was consistent to that of sounding data, which could reflect the annual variation of water vapor content over North China. Two reanalysis data showed similar annual variation to measured value, but they were systemic higher and ERA-40 reanalysis data could reflect increase trend.