1979—2012年中国西北地区东部低层水汽异常特征及成因

利用1979-2012年ERA-Interim全球再分析比湿与风场资料,通过累计距平分析、M-K突变检验、相似离度分析等方法研究了中国西北地区东部低层水汽演变特征,并依据导致水汽异常最直接的动力因子(风场差异)对其成因进行了初步探讨。结果表明:近30年西北地区东部低层700 hPa水汽呈弱的增加趋势,整个区域、青海高原区及西风影响区在1996年出现由减少到增多的突变,而季风边缘区的突变发生在1991年;且突变后偏西风减弱,偏南风增强显著。通过定量细化分析各气候区风场变化对水汽的影响,发现青海高原区经向风对水汽除夏季为弱的负贡献外,一般均表现为正贡献,而纬向风为负贡献;季风边缘区年平均经向风正贡献值为0.28 g·kg^-1,纬向风为-0.46 g·kg^-1;西风影响区冬春两季经纬向风一般均为弱的负贡献,夏秋两季一般为正贡献。依据特定区域、典型月份风场的气候型态差异分析,发现单一区域内的低层风偏差对水汽分布的影响与控制相差甚大,而不同背景下相邻区域内的风场配置及不同区域间的风场相互作用可能是水汽变化或异常的主要原因。

The Anomaly Characteristics and Causes of Low-level Water Vapor over the Eastern Part 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 annual lower-level water vapor increased in recent 30 years. 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. 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 0.28 g·kg^-1 and -0.46 g·kg^-1 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.