拉格朗日水汽源诊断方法在三江源区的应用

以NCEP/NCAR每日4次的GFS (Global Forecast System) 再分析资料驱动大气三维输送模式FLEXPART (Flexible Particle Model), 借助于拉格朗日水汽输送和源区识别技术, 在考虑了空气块输送过程中的比湿变化基础上, 诊断三江源区大气的水汽来源、输送途径及其空间结构特征。结果表明:夏季三江源区短时输送 (6 d内) 的水汽主要来自于青藏高原以及其西北侧陆地区域, 而更长时间 (8~10 d) 的来源可追踪到阿拉伯海和孟加拉湾等远距离海洋区域; 水汽输送通道主要有两支, 第1支为沿着索马里海到阿拉伯海的跨赤道水汽输送, 第2支为在西风控制下从中亚乃至西亚地区向三江源区的输送。定量分析亦显示:6月青藏高原西侧的水汽输送贡献最大, 7月阿拉伯海成为了主要水汽来源, 8月阿拉伯海水汽输送贡献减小。

Application of Lagrange Water Vapor Source Diagnosis Method to the Three river Source Area

The Three-river Source (TRS) region locating at the Tibet Plateau hinterland, contains a huge resources, gives birth to several world famous rivers, and supplies fresh water resources for East Asia. Identification of the regional moisture source is of great significance for understanding of regional water budget and improving the ability of water resources management. Ensemble modeling method is used with the three-dimensional Lagrangian transport model FLEXPART (Flexible Particle Model), driven by the GFS (Global Forecast System) reanalysis data (four times one day) from NCEP/NCAR. Then, the water vapor transport and source identification technology is used to identify the main moisture source for TRS region, with consideration of the spesific humidity changes along their transport pathways. The result indicates that a large number of air parcels experience several surface-atmosphere water vapor cycle process before reaching the TRS region. Dominated by the moisture transport form the prevailing westerlies and the central Asia strong evaporation, moisture sources characterized by relative short time transport (less than 6 days) mainly come from the Tibetan Plateau and its northwest edge, while the moisture sources with longer time (8-10 days) can be traced backward to the Arabian Sea, the Bay of Bengal, and so on. The water vapor reaching the TRS region transport can roughly be categorized to two pathways: The first is along the Somali to the Arabian Sea water vapor transport across the equator, and the second is the west path controlled by the west wind, transport from central Asia and west Asia to TRS region. Quantitative analysis shows that the moisture source also exhibits obvious sub-seasonal variability during the summer, characterized by the leading source area located in the west side of TRS region in June, and the Arabian Sea in July. However, the contribution from the Arabian Sea decreases and the contribution from the Bay of Bengal increases in August. Throughout the summer, the North of the Plateau maintains a stable water vapor transport.