Exploring the excess of cloud condensation nuclei and rain suppression using a minimal three-dimensional Boussinesq model with bulk cloud microphysics.

This article focuses on the development and application of a simplified three-dimensional numerical model to investigate how cloud condensation nuclei (CCN) concentration and vertical distribution affect rain formation and precipitation intensity. Using four distinct CCN vertical profiles—two with single-layer and two with double-layer CCN distributions representing polluted and low-polluted scenarios—the simulations reveal that a high concentration of CCN confined to a single layer near the surface tends to suppress precipitation by stabilizing the atmosphere and inhibiting condensation. In contrast, the same total CCN concentration distributed over two layers enhances rain formation, invigorates convection, and produces higher cloud tops and longer-lasting precipitation events. These findings underscore the importance of CCN vertical profiles in modulating warm-rain microphysical processes and suggest that aerosol distribution, not just concentration, critically influences precipitation outcomes in atmospheric models.