The Atmospheric Vortex Streets and Their Impact on Precipitation in the Wake of the Tibetan Plateau

Abstract

Atmospheric vortex streets (AVSs) are often observed in the wake of the leeward side of mountainous islands and are considered atmospheric analogs of the classic Kármán vortex street when a fluid flows past a cylindrical obstacle. The prevailing westerlies were observed year-round around the Tibetan Plateau. However, it remains to be understood whether the wake on the leeward side of the Tibetan Plateau exhibits a stable AVS and how the AVS impacts precipitation over the downstream region. In this study, the environmental meteorological factors, spatiotemporal characteristics, and various properties of the AVS on the leeward side of the Tibetan Plateau were examined for the period of 1979–2018 using global reanalysis datasets. The results show that the spatial structure of these AVSs closely resembles that of the classic Kármán vortex street observed in the laboratory. The meteorological factors satisfy the conditions in which a stable AVS can exist year-round. Moreover, various properties of these AVSs, including the aspect ratio and Strouhal number, are similar to those in previous studies of smaller obstacle caused AVS. Thus, these AVSs on the leeward side of the Tibetan Plateau can be interpreted as the atmospheric analog of classic Kármán vortex streets. The results further show that the spatiotemporal structure of precipitation over the wake of the Tibetan Plateau was largely shared by the cyclonic activities in the AVS. Approximately 80–90% of the total precipitation and heavy rain days in the main rainband over the wake of the Tibetan Plateau are closely tied to the seasonal evolution of the AVS.