Characteristics of water vapor content and its influencing factors in summer over Northern China

Based on the radiosonde data from 14 sounding stations and the NCEP/NCAR reanalysis data from 1979 to 2008 over the Northern China,the temporal and spatial distributions of water vapor content in summer and its influencing factors such as circumfluence were analyzed using methods of a linear trend and a Mann-Kendall mutation test as well as a composite analysis.The results show that water vapor content decreases with the increase of latitude from the southeast coastal areas to northwest inland areas over the Northern China,namely,it is wet in the southeast and is dry in the northwest.On the whole,the water vapor content in summer is in a slightly increasing trend in recent 30 years,and it has an obviously abrupt change on the late 1980s.Whether or not there is obvious water vapor convergence to North China from South China Sea to the western Pacific and whether or not there is water vapor transportation to North China in westerly belt in middle latitude for the years when there is more or less water vapor content will lead to the surface temperature high or low on the whole.The location of subtropical high moves to westward and the intensity is stronger for the year when there is more water vapor content at 500 hPa height fields.