Turbulence-induced Non-Monotonic Influence of Aerosols on Cloud Droplet Size Distribution

Cloud droplet size distribution is essential for quantifying the role of clouds in earth system, including cloud albedo, precipitation formation, and cloud lifetime. The response of cloud droplet spectral relative dispersion (ε) to aerosol number concentration (N_a) is highly uncertain, and the role of turbulence in ε–N_a relationships is yet puzzling. This study uses large eddy simulation to examine the ε–N_a relationship and derives an expression for ε from a minimal model to elucidate this relationship. Our findings indicate that as N_a increases, ε initially decreases due to the aerosol’s effect on weakening the intensity of turbulence-induced broadening greater than its effect on weakening the intensity of condensational narrowing. However, as N_a continues to increase, ε increases due to the aerosol’s effect on weakening the intensity of condensational narrowing more significant than its effect on weakening the intensity of turbulence-induced broadening. These findings improve the understanding of the aerosol effects on cloud droplet size distribution and address the challenge of quantifying aerosol indirect effects considering turbulence, potentially leading to new cloud microphysics parameterizations.