Key statistical features and common formation mechanisms of mesoscale vortices over Tibetan Plateau: A 42-warm-season analysis based on ERA5 data

During warm seasons, the Tibetan Plateau serves as a key source region for mesoscale vortices, which significantly influence weather patterns over and around the plateau. Despite extensive research on Tibetan Plateau mesoscale vortices (TMVs), no studies have examined statistical characteristics of shorter-lived TMVs (< 6 hr), and no studies have ever shown the TMVs’ vertical-extent features, common formation mechanisms, and hourly diurnal variations. To address these knowledge gaps, we conduct a statistical analysis on the TMVs over 42 warm seasons (from 1979 to 2020) by using the hourly ERA5 data. The findings reveal that TMV formation is mainly terrain-dependent, with higher frequencies occurring in regions of greater altitude. Over 68% of TMVs exhibit a lifespan of < 6 hr, and more than 75% of TMVs have a vertical extent of ≤ 50 hPa. Precipitation associated with TMVs accounts for ~ 13.8% of the total accumulated precipitation over the plateau, contributing up to ~ 36% in certain regions of the northwestern and central plateau. TMVs exhibit a diurnal peak in occurrence frequency around 22:00 local solar time. TMV formation is mainly driven by vertical stretching due to low-level convergence. TMVs are more likely to form under environmental conditions characterized by warmer surface temperatures, higher convective available potential energy, heavier precipitation, stronger upper-tropospheric divergence, and greater mid-tropospheric cyclonic vorticity. A strong steering flow, an intense vortex intensity, a large vertical extent, and a rapid enhancement in the upper-level cyclonic-vorticity are crucial for the TMVs’ moving out from the Tibetan Plateau.