Impact of dust aerosol on different grades of precipitation over the Tibetan Plateau: a case simulation study

The Tibetan Plateau (TP), known as the "Asian water tower," suffered severe desertification internally, with dust aerosol being an important factor affecting precipitation. Clarifying the role of dust aerosol in precipitation is essential. The Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) was employed to simulate a precipitation event occurring over the Tibetan Plateau from June 27 to June 30, 2008, and examined the effects of dust aerosols on different grades of precipitation in the region, with a focus on vertical motion and cloud microphysical properties. The results indicate that TP dust aerosol has different effects on different grades of precipitation by altering the macroscopic conditions and microphysical properties of the cloud. The dust aerosol facilitated heavy rainfall, increasing the 24-hour accumulated precipitation by 20.5%, while it exhibited an inhibitory effect on light rainfall, decreasing precipitation by an average of 13.0%. Overall, dust aerosol led to a 4.96% increase in total precipitation. The mechanism for this effect is that the dust aerosol increased the vertical velocity during heavy rainfall, with the maximum increment exceeding 0.06 m·s⁻¹. Additionally, dust aerosol reduced the vertical velocity during light rainfall, inhibiting its upward motion. Dust aerosol increased both cloud water mixing ratio and rainwater mixing ratio, with the growth in mixing ratio under heavy rainfall approximately eight times greater than that under light rainfall. Furthermore, dust aerosol increased the number concentration of ice particles under different grades of precipitation and lowered the cloud-top temperature and prolonged cloud lifespan.