Climatology and Structures of Southwest Vortices in the NCEP Climate Forecast System Reanalysis

AbstractThe southwest vortex (SWV) is a meso-α-scale cyclonic low pressure system originating in southwest China. It is a high-impact precipitation-generating weather system in this region and a large downstream area. A climatology of the SWV over 1979–2010 is presented here. Results indicate that the SWV is a common regional weather system with about 73 annual occurrences. Two primary genesis regions are identified, one in the Sichuan basin and another one in the southeast flank of the Tibetan Plateau. SWV genesis displays seasonality with a spring–summer preference and diurnal variations. The average life cycle, horizontal dimension, and translation speed are 15.1 h, 435 km, and 8.6 m s−1, respectively. SWVs are classified into four types that show regional and seasonal contrasts in structure. In type I, the winter–spring elevated dry vortex in the basin is vertically confined to a shallow layer between 850 and 600 hPa and tilts northeastward. The low-level vortex has a cold center, and the middle to up...