Non-Monotonic and Structurally Dependent Precipitation Responses to Dust Ice Nuclei in a Quasi-Stationary Southwest Vortex

The Southwest Vortex (SWV) is a major meso-α-scale system responsible for heavy rainfall over the Sichuan basin, yet the role of dust aerosols—particularly their ice-nucleating (IN) effects—in modulating SWV precipitation remains poorly understood. In particular, whether and how such effects vary across different radial regions and evolutionary stages of the vortex has not been systematically examined. Clarifying this structural dependence is critically important for reducing uncertainties in heavy-rainfall forecasts over complex terrain regions of Southwest China, where long-range transported dust frequently intersects with SWV activities but is largely overlooked in operational models. Using the Weather Research and Forecasting Model‌ version 4.3 (WRF v4.3) with the Thompson aerosol-aware microphysics scheme, we simulate a quasi-stationary SWV event that occurred on 12–13 August 2020. Three sensitivity experiments—LowDust, MediumDust, and HighDust—are designed based on the 20-yr August climatology of the the ECMWF Copernicus Atmosphere Monitoring Service (CAMS) global reanalysis (2003–2022), with hydrophilic cloud condensation nuclei (CCN) concentrations held constant across all runs to isolate the pure IN effects of dust. The vortex domain is divided into inner (0–60 km), middle (60–120 km), and outer (120–180 km) radial zones to assess structural dependencies. Precipitation responses to increasing dust loading exhibit strong spatial heterogeneity and non-monotonic behavior. During the mature stage, as dust increases from Low to Medium, precipitation in the inner circle rises from 0.47 to 0.67 mm (10 min)⁻¹, while it declines in the middle and outer circles. Further increasing dust from Medium to High reverses this trend. During the decaying stage, inner-circle precipitation decreases monotonically, whereas the middle and outer circles show an initial increase followed by a decrease. These disparities are governed by a vortex dynamic “competitive effect” that redistributes liquid water among regions according to local convective intensity, thereby altering snow/graupel production, latent heat release, and ultimately precipitation distribution. Dust IN effects on microphysics and precipitation are strongly dependent on convective intensity and vortex structure, becoming negligible during the dissipating stage. This structural dependence provides a process-level framework for understanding aerosol–precipitation interactions in mesoscale vortex systems and offers a physical basis for improving their representation in regional numerical weather prediction models.