Impact of Coarse-Mode Aerosol on Jiangxi Warm Clouds Considering Different Updraft and Activation Intensities: An SBM-FAST Approach

Abstract. The effects of different aerosol modes on warm clouds vary, with coarse-mode aerosols having a unique influence on cloud droplet growth and cloud-rain auto-conversion. Therefore, understanding the influence of coarse-mode aerosol concentrations on warm cloud formation and development is critical for improving weather prediction models and climate projections. This study uses the SBM-FAST scheme in the WRF model to assess how variations in coarse-mode aerosol concentrations (Ncm) affect the macro and micro characteristics of warm clouds in Jiangxi, China, focusing on the impacts under different updraft (W) and activation intensities through sensitivity experiments. Results indicate that higher Ncm enhances early-stage droplet number concentrations at the cloud base, accelerate cloud development. Increased Ncm also promotes earlier collision-coalescence processes, with more active formation and coalescence of larger droplets at higher Ncm concentrations. Yet, the response of cloud microphysics, like droplet concentration and relative dispersion (ε), to Ncm changes is not linear, depending on the combined effects of updraft strength (W) and cloud droplet activation. Lower W/activation ratios lead to lower droplet activation in suboptimal supersaturation, reducing average size but enhancing ε of cloud droplet. The number concentration of cloud droplet present initial decline then rise trend with increasing Ncm, which reflects the balance between the aerosol-activation replenishment and collision-coalescence depletion of small size cloud droplet, illustrating the nonlinear influence jointly caused by aerosol activation and droplet interactions.