Abstract

Aerosols are postulated to alter moist convection by increasing cloud droplet number concentration. Cloud-resolving model simulations of radiative-convective equilibrium show that increased cloud droplet number concentration leads to higher convective mass flux, seemingly in line with a popular hypothesis which links the convective invigoration to delayed rain formation allowing more cloud liquid water to be frozen. Yet, the same phenomenon is also present in an alternative model configuration with only warm-rain microphysics, suggesting that one does not have to invoke ice microphysics. The key mechanism lies in the different vertical distributions of the increases in cloud liquid re-evaporation and in water vapor condensation, causing a dipole pattern that favors convection. This is further supported by a mechanism-denial experiment in which weakened cloud re-evaporation tends to mute invigoration. This work represents a major advancement of the process-level understanding of aerosol effects on convection.