Application of Potential Vorticity Analysis in Forecasting the Heavy Rain in Xinjiang

Based on the potential vorticity theory,the relations between the PV(potential vorticity)and the precipitation or heavy rain occurred in Xinjiang region are preliminarily studied in this paper through a heavy rain case caused by Central-Asia vortex from July 18 to 20,2004.The results show that the dry PV in the upper troposphere can well reflect both the cold and warm air flow motions and present the developing features of the weather system,and the PV can trace the cold air flow more clearly than the temperature or height field,which provides a new idea for the study of the cold air flow motion,especially its role in triggering a heavy rain.The moist PV in the lower troposphere has good relations with the intensity of the precipitation.It is favourable for causing a rain when the moist isentropics are very stiff,which can lead to the development of slantwise vorticity,and a heavy rain will probably happen in the stiff and dense section of the moist isentropics when MPV0.