Numerical Simulation on a Heavy Snowfall/Freezing Rain Process in January 2008

Based on the 1°×1° NCEP/NCAR reanalysis and daily observational datasets, the mesoscale model WRF was used to simulate a Heavy Snowfall/Freezing Rain Process occurred in the area of the middle and lower reaches of the Yangtze River from 25 to 29 January 2008. The results indicate that the WRF model can successfully simulate the characteristics of the circulation's evolution on high and low level. The distribution of precipitation area and precipitation cell can also be well simulated. Diagnoses of the output data show that the vapor transported by the Southwest low altitude jet flow made a humidity province in the middle and lower reaches of the Yangtze River basin and prepared sufficient moist conditions for the heavy snowfall/freezing rain. The analyses on the characteristics of the cloud microphysical processes of heavy snow/freezing rain show that there is an inversion layer from 600 to 900 hPa which is related closely with the heavy snow/freezing rain. The precipitation particles was melted by inversion layer with the temperature of above 0 ℃ into excessive cooling water which was quickly freeze up when it encountered cold surface whereas the temperature of melting layer is below 0 ℃ in the formation of snow.