Research On Collaborative Characteristics And Causes Of Low-level Water Vapor And Wind Over The East Of Northwest China

By using the ERA-Interim global reanalysis wind and specific humidity data from 1979 to 2012, the evolution characteristics of low-level water vapor are analyzed with the methods of variation rate analysis, Mann-Kendall test and analogy deviation analysis. And based on the wind field difference, the moisture abnormality is preliminarily discussed. Results showed that:The 700hPa vapor over eastern part of Northwest China showed a reduced distribution from southeast to northwest and mainly concentrated in May to September.In addition, the annual lower-level water vapor increased in recent 30 years and the cumulative anomaly showed a bimodal structure, peaking appeared in 1987 and 1997.Moisture was abundant in Qinghai Plateau and the monsoon region, relatively little moisture in arid desert area. Water vapor changes in Qinghai Plateau were formed by the west east winds together, the maximum moisture content appears in summer,for the southeast wind transport plays a major role; Shan-ganning plateau is located at the northern edge of the East Asian monsoon region, water vapor in this area largely affected by meridional wind; Besides water vapor in westerly affected zone is mainly affected by the westerly moisture transport, there is a close relationship with changes in zonal westerly winds.Water vapor at 700hPa over eastern part of Northwest presents a mutation characteristic of reduced to increase.In the Qinghai Plateau and arid desert region, water vapor happened abrupt change in 1996, while in 1991 for the monsoon region. Furthermore, westerly winds weaken and southerly winds increased significantly after abrupt change occurred. This suggests that the eastern part of the Northwest enhanced southerly moisture vapor transport from the south-east direction, which is one of the reasons for water vapor increase in recently 34a over this area.Through quantitative analysis of the impact of wind field change on water vapor, we found that meridional wind positively contributed to water vapor in the Qinghai Plateau region, except negative contribution in summer, and zonal wind showed negative contribution. The meridional and zonal contribution were 0.28g-kg-1 and-0.46g-kg’’in the monsoon region, respectively. In arid desert region, wind’s contribution appeared positive in winter and spring, while negative in summer and autumn.Based on the wind’s climatic pattern differences in specific regions and typical months, we found that influence of low-level wind field change on the distribution of water vapor was much more different within a single region. However, the configuration of wind fields in adjacent areas in different backgrounds and wind interaction between different areas are the main reasons for the change of water vapor.