A Climatology of the Southwest Vortex during 1979–2008

Abstract

AbstractUsing a new vortex detection and tracing method, a dataset of the Southwest Vortex (SWV) is established based on Japanese 25-year Reanalysis (JRA-25) reanalysis data during 1979–2008. The spatiotemporal features of the SWV are derived from the dataset. In comparison to other seasons, summer yields the least SWVs, but with the highest probability that they will migrate from their region of origin. SWVs mostly emerge in the southwest of the Sichuan Basin and the southeast of the Tibetan Plateau. Migratory SWVs mainly move along either an eastward or southeastward path. Detailed composite analysis of warm-season SWVs shows that the subtropical high is a key factor in determining the direction of migratory SWVs. Furthermore, the steering wind at 700 hPa dominates the moving direction of migratory SWVs. Potential stability diagnosed by pseudo-equivalent potential temperature θse is of certain significance for the evolution and movement of SWVs. On the other hand, migratory SWVs possess relatively great...