Genesis of southwest vortices and its relation to Tibetan Plateau vortices

SWVs are important summer rain-producing systems over southwestern China, and even wider areas in eastern China when they move eastward. Based on the final analyses data (FNL) of the Global Forecasting System of the National Centers for Environment Prediction, the role played by Tibetan Plateau vortices (TPVs) in the genesis processes of vortices in southwest China, referred to as southwest vortices (SWVs) is investigated. Since the TPVs and SWVs are most active in summer, the cases in May August are studied. It is revealed that the TPVs moving off the Tibetan Plateau (moving-off TPVs) can exert significant effects on the genesis of SWVs through both dynamic and thermodynamic processes. The moving-off TPVs are favourable for the generation of SWVs through strengthening the cyclonic vorticity, convergence and ascending motion. Diagnoses of the potential vorticity budgets reveal that the condensational latent heat has the greatest contribution to the generation of SWVs. Analysis of the water vapour budget indicates that the water vapour is mainly transported from south of the genesis region of SWVs associated with strong southerlies. It is demonstrated that the southerlies and associated water vapour transport are another prominent factor affecting the genesis of the SWVs.