Study of the influence of the different horizontal resolutions and microphysical setups on the idealized simulation of a squall line

Using the WRF (Weather Research and Forecasting) model, the idealized simulations of the 5 June 2009 squall line event in the Shanghai area are conducted in this paper for exploring the influences of the different horizontal resolutions and microphysical setups on the idealized simulations. Three different horizontal grid spacing, which are 3, 1 km and 0.5 km, and two different microphysical setups, with single-moment and double-moment microphysics, are used. The results show that the simulations of the gust front of the squall line are sensitive to both horizontal resolution and microphysical setup. The higher-resolution model has higher performance on simulating the fine structure of the bow echo in the squall line. Comparing with 3 km, the simulation with 1 km or 0.5 km horizontal resolutions can produce the front updraft and the rear downdraft of squall line clearly with similar gusts to each other. The double-moment microphysics simulations can produce the more reasonable bow echo structure of squall line and drops in temperature on the surface with slower movement, less cold pool area and intensity, less gust and less rainwater evaporation than the single-moment microphysics. Comparison against the WSR-88D observations shows that 1 km or 0.5 km horizontal resolution with the double-moment microphysics setup produces more realistic simulation than the others. The finer resolution is benefitial to simulating the evolution of squall line. For simulating the gust front of squall line, the operational NWP model maybe requires 1 km horizontal resolution with the double-moment microphysics setup. Furthermore, the evolution of gust, cold pool intensity, rate of cooling in the bottom of model, propagation of squall line and rainwater evaporation show a similar trend of evolution. The propagation speed of squall line is indicative of gust forecast. For improving the NWP performance of gust prediction, not only must horizontal resolution and microphysics setup be paid more attentions to, but also rainwater evaporation simulation must be improved.