Application of Potential Vorticity Diagnoses in Yunnan Summer Heavy Rain Forecasting

This is an approach to application of the potential vorticity diagnosis technique to Yunnan heavy rain forecasting through one of most often occurring strong precipitation cases so-called as \!Yunnan-Guizhou convergence pattern summer. The main results are as follows: Both the dry and moist potential vorticity(PV) can well present the features of the weather systems. The dry PV reflect both the cold and warm air flow activities. The upper tropospheric dry PV tends downward to the lower-levels and vice versa for the lower-level troposheric dry PV. It is favourable for causing the heavy rainstorm when the dry air in upper levels meets with the warm and wet air in the lower-levels along with the convergence conditions of low and shear line in lower-layers; but once the PV weakens in upper- and lower-levels the precipitation will be ended soon. The \!Yunnan-Guizhou convergent pattern rainstorms show usually there are a dry PV high value oriented belt in NE to SW or N to S in the mid-and lower-troposhere, and when the high value belt is broken, the process of heavy rain over Yunnan will end up. The moist potential vorticity(MPV)presents the cyclones on the 700 hPa much better than the dry PV. Commonly, the conditions MPV10 and MPV20 on 700 hPa occur during the heavy rain process in Yunnan.