1958～2005年中国高空大气比湿变化

利用经过质量控制和均一化的92站探空露点温度序列，研究了中国高空大气比湿气候学特征和1958～2005年比湿时间、空间演变以及不同时段线性变化趋势地区和季节差异。中国比湿气候场特征显示，垂直方向上90%以上的水汽集中在对流层中低层，空间呈南高北低的纬向分布。通过累积距平、滑动平均和突变点分析等方法研究了中国平均高空比湿的年代际变化，得到1958～2005年中国对流层中低层大气比湿经历“湿”、“干”、“湿”阶段性变化。不同时段线性变化趋势分析表明，1958～2005年对流层低层比湿呈上升趋势，对流层中层、高层和平流层下层为下降趋势；1979～2005年对流层低层上升趋势和对流层高层下降趋势均较整个时段明显增强。近50年来中国高空各层温度与比湿变化基本同步，统计达到显著相关，说明温度是影响比湿变化的重要因子。趋势的空间分布显示对流层下层全国大部比湿为上升趋势，且1979以来上升趋势更加明显，对流层中层趋势呈北升南降分布，对流层高层多为下降趋势。中国五个分区中西北地区对流层低层比湿上升趋势最明显，长江和华南地区升幅较小。1958～2005年对流层下层各季节比湿变化趋势差异较明显，上升趋势发生在夏、冬两季，1979～2005年四季比湿均呈上升趋势，其中夏季上升趋势最为明显。

Upper-Air Specific Humidity Change over China during 1958-2005

The changes in the upper-air specific humidity during 1958-2005 were studied based on time series of homogenized radiosonde dewpoint data from 92 selected stations in China. The data suggest that in the vertical direction more than 90% of water vapor is concentrated in the lower and middle troposphere, and the horizontal structure shows zonal distribution decreasing with latitude. Temporal analysis of the annual specific humidity time series by using the moving average and accumulation anomalies shows decadal variability in the lower and middle troposphere with negative anomalies from late 1960s to early 1980s and positive anomalies after the late 1980s. The linear trend of the average specific humidity in China is positive in the lower troposphere and negative above the mid-troposphere for 1958-2005. During 1979-2005, a positive trend in the lower troposphere and a negative trend in the lower stratosphere were both prominent. Time series of temperature and specific humidity in the troposphere and lower stratosphere simultaneously changed during 1958-2005; furthermore, their correlations at all levels are statistically significant, which suggests that temperature strongly affects the specific humidity changes. The spatial distribution of the linear trend suggests that the specific humidity in the lower troposphere increase in most stations during 1958-2005 and the increasing trends are more obvious after 1979. In the mid-troposphere, negative trends are in the regions south of the Yangtze River and positive trends are in the rest of China. The analysis of the vertical profiles of the linear trends in five subregions of China shows that the highest positive trends are over Northwest China and slightly positive trends are over the regions south of the Yangtze River in the lower and middle troposphere. During 1958-2005, the trends of seasonal specific humidity in the lower troposphere exhibit obvious differences with a wetting trend in the summer and winter, and a drying trend in spring and autumn. In contrast, during 1979-2005, the specific humidity trends for all seasons are consistently positive, and the wetting trend in the summer is more prominent in the lower and middle troposphere.