ABSTRACT Aerosol effect on orographic clouds and its feedback on the surrounding meteorological environment have been investigated using the Weather Research and Forecasting Model with the spectrum bin microphysics scheme. Analysis of aerosol impacts on water vapor mixing ratio, latent heating rates, and wind field reveals that enhanced aerosol loading invigorates convection accompanied by intensive latent heat release, which induces stronger convergence at 3–5 km of altitude and leads to increased horizontal wind speed around the periphery of clouds on the windward slope. Moreover, the enhanced negative buoyancy around the periphery of clouds under polluted condition induces the descent of dry air from the middle troposphere, together with the downslope winds, consequently resulting in lower humidity and higher temperature at lower levels of the lee side. Under clean condition, the surface temperature of the leeward slope is 6.0 K higher than that of the windward slope, while this difference is increased to 7.0 K under polluted condition. The surface relative humidity on the lee side is 42.6% and 21.6% for clean and polluted conditions, respectively. By intensifying the downslope wind and reducing leeside humidity, aerosols suppress subsequent cloud growth and thereby alter the precipitation pattern, leading to higher rain rates over the windward slope and leeward side under polluted and clean conditions, respectively.
Zhang et al. (Sun,) studied this question.