Effect of the Choice of Model Microphysics Scheme on Heavy Mei-Yu Rainfall Simulations

A better simulation and prediction of Mei-yu front heavy rainfall are critical for flood management in the Yangtze River Valley, China. The impact of three cloud microphysical schemes of the WRF model on the simulated heavy Mei-yu rainfall in central China that occurred during a 30-hour period in July 2016 is examined. A comparison with surface precipitation observations indicates that overall spatial distribution of precipitation is captured by all three schemes. After an examination of microphysical budget analysis in the model, it is found that accretion of cloud droplet by raindrop and melting of ice phase hydrometeors are prevailing processes to the growth of raindrop, though these two processes differ significantly among the three microphysics schemes. Additionally, Bergeron and riming processes play a dominant role in the growth of ice phase hydrometeors in simulated Mei-yu rainfall. The latter process differs most, which contributes to the large distribution difference in three schemes. The terminal velocity of raindrop (Vr) is overestimated leading to overestimation of rainfall. And the Thompson scheme shows better agreement with measured precipitation, a result of the cancellation of terminal velocity bias of opposite signs at different ranges of raindrop diameters.