Sensitivity of convective cloud and rainfall responses to urban aerosol emission strengths

Abstract. Urban aerosol emissions can modify convective precipitation through aerosol-cloud interactions, yet the sensitivity of convective events to emission strength and its detectability against meteorological variability remain poorly constrained. We investigate aerosol-cloud-precipitation interactions using the COSMO-DCEP-MUSCAT model system with direct aerosol-cloud coupling, systematically varying urban emission strengths across a wide scaling range for two differing mid-latitude convective cases. Lagrangian trajectory analysis tracks air volume transport from urban sources into convective regions, complemented by ensemble simulations to separate emission-induced changes from natural meteorological variability.

Results reveal a strong dependence on meteorological conditions. Under moderate convective instability, high emission scaling factors trigger ice-phase invigoration through enhanced ice nucleation and latent heat feedback, producing substantial increases in ice content and precipitation intensity accompanied by spatial expansion and temporal shifts. Emission-response analysis reveals nonlinear behavior, with low-to-moderate scaling factors producing no systematic response while high scaling factors trigger substantial microphysical modifications. Under stronger convective instability, even the highest emission scaling factors produce only modest microphysical responses and spatial redistribution rather than intensification, as strong background dynamics buffer aerosol-induced impacts. Ensemble analysis demonstrates that robust signals emerge only for selected variables during specific convective stages, with most responses remaining comparable to natural atmospheric variability.

These results indicate that detectable precipitation responses require strong emission perturbations under favorable meteorological conditions, with effects manifesting as intensity changes and spatial and temporal redistribution. The convective regime critically determines the magnitude and detectability of aerosol effects, with implications for understanding urban impacts on precipitation across different atmospheric environments.