Impacts of long-range transported mineral dust on summertime convective cloud and precipitation: a case study over the Taiwan region

Abstract. As one of the most abundant atmospheric aerosols and effective ice nuclei, mineral dust particles affect clouds and precipitation in the Earth system. Here numerical experiments are carried out to investigate the impacts of dust aerosols on summertime convective clouds and precipitation over the mountainous region in Taiwan. We run the Weather Research and Forecasting model (WRF) coupled with the spectral-bin microphysics (SBM) and Morrison two-moment (Morr2) schemes at 3 km resolution, with the dust number concentrations from a global chemical transport model (GEOS-Chem-APM). The case study indicates that the long-range transported dust, with relatively low number concentrations, can notably affect the properties of convective cloud (ice/liquid water contents, cloud top height, and cloud coverage) and precipitation (spatial pattern and intensity). The dust effects are evident during the strong convective periods, significantly increasing the ice water contents in the mixed-phase regime via the enhanced heterogeneous freezing. With both the Morr2 and SBM schemes, we see invigoration effects of dust aerosols on the convective intensity through enhanced condensation and deposition latent heating. In this process, the low-altitude dust particles are uplifted to the freezing level by updrafts which, in turn, enhance the convective cloud development through immersion freezing and convective invigoration. Comparing to the Morr2 scheme, the SBM scheme predicts more realistic precipitation and different invigoration effects of dust. The differences are partially attributed to the saturation adjustment approach utilized in the bulk scheme, leading to the stronger enhancement of condensation at mid-low altitude and weaker deposition increase at the upper level.