POTENTIAL VORTICITY ANALYSIS OF AN TORRENTIAL RAIN TRIGGRED BY A NEUTERCANE IN SHANDONG PROVINCE

By using the numerical model MM5V3,a successful simulation was made for a torrential rain in Shandong province triggered by a neutercane during 11th to 12th in August 1999. Using simulated information and the theory of potential vorticity (PV), the dynamical mechanism by which the torrential rain occurred and developed was analyzed. The results show that weak cold air spreading into the typhoon and tropical convergence stretching northward mainly resulted in the torrential rain. The conservation theory of PV can well explain why the torrential rain and mesoscale vortex occurred and developed. The PV disturbance of the upper troposphere is an important factor for the mesoscale vortex and torrential rain to occur and develop. The wind and pressure on the 345K isentropic surface revealed physical mechanisms that see southeastward warm-moist flow uplifting along the isentropic surface and meeting with descending cold air, which resulted in convection and the torrential rain.