Impact of transported dust aerosols on precipitation over the Nepal Himalayas using convection-permitting WRF-Chem simulation

In this study, we implemented a convection-permitting Weather Research and Forecasting model coupled with chemistry (WRF-Chem) to assess the impact of the long-range transported dust aerosols on the precipitation and convective processes over the Nepal Himalayas. A substantial amount of dust aerosol was transported to the Central Himalayan region during the dust storm event that occurred from 12 to 15 June, 2018 in the Thar desert, northwestern India. Two different sensitivity simulations, with and without transported dust aerosols, in a cloud-resolving scale of 3 km horizontal resolution was performed. We isolated the long-range transported dust aerosols by zeroing out dust aerosols from lateral boundary conditions and keeping all other locally emitted and remotely transported aerosols from anthropogenic, biogenic, and biomass burning sources. The simulation results show the noticeable impacts of transported dust aerosols on the cloud microphysical properties and regional precipitation over the southern slopes of the Nepal Himalayas. In comparison to the simulation without dust, precipitation is enhanced by 9.6% over the mountainous terrains (500–3000 m) in the presence of dust aerosols. An activation of dust aerosols as condensation nuclei significantly increased the droplet concentration resulting in enhanced convection and upward velocity with the release of latent heat of condensation. Though we simulated one event of long-range transported dust aerosols and some biases in simulation exist, this study highlights the discernible impact of remote dust aerosol on the convection and cloud microphysical properties, which can significantly influence the regional precipitation and Himalayan hydrology.