Summer Atmospheric Water Cycle under the Transition Influence of the Westerly and Summer Monsoon over the Yarlung Zangbo River Basin in the Southern Tibetan Plateau

Abstract

This study compares the summer atmospheric water cycle, including moisture sources and consumption, in the upstream, midstream, and downstream regions of the Yarlung Zangbo River Basin in the southern Tibetan Plateau. The evolutions of moisture properties under the influence of the westerly and summer southerly monsoon are examined using 5-yr multi-source measurements and ERA5 reanalysis data. Note that moisture consumption in this study is associated with clouds, precipitation, and diabatic heating. Compared to the midstream and downstream regions, the upstream region has less moisture, clouds, and precipitation, where the moisture is brought by the westerly. In early August, the vertical wet advection over this region becomes enhanced and generates more high clouds and precipitation. The midstream region has moisture carried by the westerly in June and by the southerly monsoon from July to August. The higher vertical wet advection maximum here forms more high clouds, with a precipitation peak in early July. The downstream region is mainly affected by the southerly-driven wet advection. The rich moisture and strong vertical wet advection here produce the most clouds and precipitation among the three regions, with a precipitation peak in late June. The height of the maximum moisture condensation is different between the midstream region (325 hPa) and the other two regions (375 hPa), due to the higher upward motion maximum in the midstream region. The diabatic heating structures show that stratiform clouds dominate the upstream region, stratiform clouds and deep convection co-exist in the midstream region, and deep convection systems characterize the downstream region.