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A Study on the Trend in Upper Tropospheric Water Vapor over the Tibetan Plateau in Summer
许曦然
兰州大学
Using various reanalysis datasets combined with measurements of the Aura Microwave Limb Sounder (MLS), the long-term trend of water vapor in the upper troposphere over the Tibetan Plateau (TP) and its possible mechanisms are studied. It is found that the variation of water vapor at 200 hPa over the TP in the summer reflected by the ERA-Interim reanalysis product is closer to the MLS satellite. In the past 38 years, the increase in surface temperature over region 1 (34°N-38°N,86°E-100°E) has caused snow melting and enhanced surface evaporation, leading to more water vapor in the upper troposphere. At the same time, the intensification of convective activity has also enhanced vertical transport, which results in increased water vapor at 200 hPa over region 1. The contributions of surface temperature and convective activity to the positive trend of water vapor at 200 hPa in this region are 143.2% and 19.7%, respectively. The increase in water vapor over region 2 (27°N-35°N,80°E-90°E) is largely attributed to enhanced convective activity, which increases vertical transport of water vapor in the atmosphere. In addition, the South Asian High (SAH) increases the suction effect in the lower atmosphere. Over the area controlled by the SAH, water vapor is confined within the scope of the anticyclone and slowly transported upward, increasing the water vapor content in the upper troposphere. The contribution of convective activity and SAH to the positive trend of water vapor in region 2 is 76.6% and 76.2%, respectively. The negative trend of water vapor over region 3 (27°N-31°N,92°E-98°E) is mainly due to the weakening of water vapor transport caused by the weakening of convective activity. The contribution to the negative trend of water vapor is 105.5%.