Impacts of aerosols on the development and precipitation of a mesoscale squall line

The effects of aerosols on the development and precipitation for a mesoscale squall line occurring in the south plains of the United States have been investigated using a cloud-resolving Weather Research and Forecasting (CR-WRF) model with a two-moment bulk microphysical scheme. Different aerosol scenarios are considered in the CR-WRF model experiments, including polluted continental aerosols with a mean concentration of 2000 cm(-3). The simulated temporal evolution of composite radar reflectivity and the 24-h accumulated precipitation in the polluted aerosol experiment are in agreement with the measurements. The influence of aerosol concentrations is insignificant on the rainfall distribution but is remarkable on the precipitation intensity. The CR-WRF experiment with the polluted aerosol case predicts about 13% more precipitation and more locally intensive rainfall than do those with the clean aerosol case. Both the convection zone and the storm convective strength are increased in the polluted aerosol experiment in response to the increase in aerosol concentrations. The two-moment microphysical scheme is compared with three single-moment bulk schemes in the WRF model, including the Lin, WRF single-moment six-class, and Thompson schemes. Only the Thompson schemes reproduce the observed precipitation and radar reflectivity pattern, in agreement with the two-moment scheme with a leading convective line and a trailing stratiform precipitation regime. All of the single-moment schemes significantly overestimate the precipitation, especially with the Lin scheme, while the two-moment scheme yields the precipitation simulation comparable with the measurement.