Longwave radiation responses to cloud property perturbations in blackbody clouds should not be assumed to be negligible

Abstract

The discussion of radiative cooling in cloud dynamics rarely considers quantities aside from the total radiative cooling over a cloud layer, which is constant for blackbody clouds in a given environment. However, here we demonstrate using idealized radiative transfer calculations that the total cooling in the upper part of the cloud increases with liquid water path up to ~100 g m−2, well beyond the threshold liquid water path needed for a cloud to be a blackbody. Moreover, the maximum local cooling rate increases with LWP indefinitely. We then show using high-resolution simulations that the modulation of longwave radiative cooling profiles in blackbody clouds alters the dynamics, free tropospheric entrainment rates, liquid water path, and organization of closed cell stratocumulus clouds. We suggest that the role of longwave radiation in blackbody clouds, particularly in the context of aerosol-cloud interactions, should be given more consideration.