Spatially inhomogeneous phase change, and its effect on cloud turbulence

We ask whether cloud turbulence differs from typical fluid turbulence, and answer in the affirmative: small-scale turbulence is significantly enhanced in clouds by inertial droplets. This enhancement stems from a mismatch in time scales between vortex evacuation and condensation. Inertial droplets are centrifuged out of vortical regions much faster than condensation can occur. They then grow by condensation, releasing latent heat locally. Our simulations reveal that vortical regions co-locate with cooler temperatures and higher moisture, leading to sharp density gradients at their boundaries. These gradients drive baroclinic torque, generating small-scale turbulence. The time scales involved align with our scaling estimates. While our earlier two-dimensional model anticipated this effect, it underestimated its intensity and limited it to sub-Kolmogorov scales. The enhancement of turbulence over inertial scales that we find here could drive rapid raindrop growth.