A Comparative Study of Effects of Different Microphysics Schemes on Precipitation Simulation for Typhoon Mujigae (2015)

Using GFS (Global Forecast System) data as the initial field, numerical simulations of typhoon Mujigae in 2015 were conducted using the WRF3.6.1 (Weather Research and Forecasting Model). A comparative study of four microphysical schemes (Lin, WSM6, GCE, and Morrison) with concerns of the simulated typhoon track, intensity, precipitation, and contents of hydrometeors were carried out using the best track dataset from CMA (China Meteorological Administration), MTSAT satellite data, and precipitation data collected at automatic weather stations. It is found that all the four cloud microphysical schemes can well simulate the westward movement and landfall of the typhoon. However, the simulated typhoon intensity, structure, and precipitation are quite different using the four different cloud microphysics schemes. In terms of the water content, precipitation is overestimated by the GCE scheme, while the other three schemes yield similar simulations of cloud water and rain. This result indicates that the differences among the schemes mainly exist in the simulation of cloud ice, snow, and graupel particles. Comparing the cloud physical transformation processes simulated by the WSM6 and Morrison scheme, it is found that the simulation of melting snow and graupel particles by the WSM6 scheme is better than that by the Morrison scheme, whereas the simulated strength of the conversion process between ice phase particles is weaker than that by the Morrison. The heat budget analysis for cloud microphysical process shows that strong diabatic heating is more concentrated over the eye area in the WSM6 scheme, which results in stronger warm core structure and lower central pressure than in other schemes. Detailed analysis of cloud microphysical conversion shows that the main cloud microphysics process involved in typhoon precipitation is the condensation and/or sublimation of water vapor into cloud water and/or cloud ice. The cloud water is then partly accreted directly into rainwater, and partly accreted by snow particles and form graupels, which finally become rainwater as the graupel particles descend to the melting layer. Through accretion, the cloud ice is converted into snow, while part of the snow particles collect super-cooled water droplets and rim into graupels, which then melt into rain. A considerable part of snow particles directly melt to form precipitation.