WRF-SBM Numerical Simulation of Aerosol Effects on Stratiform Warm Clouds in Jiangxi, China

Aerosols, as cloud condensation nuclei (CCN), impact cloud droplet spectrum and dispersion (ε), affecting precipitation and climate change. However, the influence of various aerosol modes on cloud physics remains controversial, and this effect varies with location and cloud type. This study uses a bin microphysics scheme (WRF-SBM) to simulate a warm stratiform cloud in Jiangxi, China. The numerical simulations reproduce the macro and microstructure of warm clouds compared with aircraft observations. Further experiments modifying the aerosol spectrum and number concentration indicate: increased aerosol concentration promotes cloud formation, raises cloud height, and broadens the cloud droplet spectrum. In contrast, a decrease in aerosol concentration suppresses cloud formation and development. Different aerosols have varying effects on the cloud droplet spectrum. Higher accumulation mode aerosol concentration increases small droplet concentration, while increased nucleation and coarse mode aerosol concentration favors larger droplet formation. Generally, the correlation between ε and volume-weighted particle size (rv) changes from positive to negative as rv increases. The transition in correlation is influenced by the relative strengths of cloud droplet collision, condensation, and activation processes. The increase in accumulation mode aerosol concentration strengthens the positive correlation between ε and rv in the rv range of 4.5–8 μm, while the decrease in concentration strengthens the negative correlation in the same range. Regardless of different coalescence intensity, ε converges with the increase in Nc. Changes in aerosol concentration for different modes do not alter the convergence trend of ε-Nc but only affect the dispersion of ε at low Nc levels.