Effects of aerosols on cloud microphysics simulations with Weather Research Forecasting (WRF) model in East Asia

Aerosols in the atmosphere play an important role in cloud formation as cloud condensation nuclei (CCN). Chemical composition and number size distribution of aerosols significantly modify cloud properties by altering droplet number concentration, droplet effective radius, cloud albedo, cloud liquid water content, and cloud lifetime. However, a mechanistic simulation of aerosol effects in cloud microphysics is relatively scarce in regional meteorological forecasting models. We examine the effect of dynamically varying aerosols on CCN activation and cloud formation in the WRF model by employing the updated Twomey equation and our improvement in the cloud microphysics scheme in particular for the CCN activation process. First, we use the Community Multiscale Air Quality (CMAQ) model to obtain spatially and temporally varying aerosol concentrations in East Asia, which are provided as input data in the WRF simulations. The baseline and sensitivity simulations are conducted using the WRF. The latter includes explicit calculation of CCN activation with aerosol concentrations from the CMAQ. A comparison of simulated precipitation with Tropical Rainfall Measuring Mission observation shows better agreement of sensitivity results with observed data. We also find that the simulated precipitation in the sensitivity model shows a clear weekly variability such as increases in precipitation during the weekdays whereas the decrease during the weekends. This simulated weekly variability is consistent with that of observed precipitation in Korea over the past decades and can be attributed to the indirect effect of anthropogenic aerosols coined as "weekend effect", indicating the importance of an explicit consideration of aerosols for cloud microphysics simulations of regional meteorological models.