Diagnostic analysis of the evolution mechanism for a vortex over the Tibetan Plateau in June 2008

Based on the final analyses data (FNL) of the Global Forecasting System ofthe NCEP and the observational radiosonde data, the evolution mechanism ofan eastward-moving low-level vortex over the Tibetan Plateau in June 2008was analyzed. The results show that the formation of the vortex was relatedto the convergence between the northwesterly over the central TibetanPlateau from the westerly zone and the southerly from the Bay of Bengal at500 hPa, and also to the divergence associated with the entrance region ofthe upper westerly jet at 200 hPa. Their dynamic effects were favorable forascending motion and forming the vortex over the Tibetan Plateau.Furthermore, the effect of the atmospheric heat source (Q₁) is discussedbased on a transformed potential vorticity (PV) tendency equation. Bycalculating the PV budgets, we showed that Q₁ had a great influence onthe intensity and moving direction of the vortex. In t Q₁ he developing stage ofthe vortex, the heating of the vertically integrated was centered tothe east of the vortex center at 500 hPa, increasing PVtendency to the east of the vortex. As a result, the vortex strengthened andmoved eastward through the vertically uneven distribution of Q₁. In thedecaying stage, the horizontally uneven heating of Q₁ at 500 hPaweakened the vortex through causing the vortex tubes around the vortex toslant and redistributing the vertical vorticity field.