Moist Convection and Radiative Cooling: Dynamical Response and Scaling

Lokahith Narendra Agasthya, Caroline Muller

Moist convection is a fundamental process occurring in the Earth's atmosphere. It plays a central role in the weather and climate of the tropics where, to first order, the heating of the atmosphere by convection is in balance with the cooling of the atmosphere by the emission of radiation to outer space. In this study, we use a Cloud Resolving Model in Radiative-Convective Equilibrium with an imposed constant rate of radiative cooling and study the response of moist convection to varying this rate of radiative cooling.
In particular, we study two types of simulation -- Varying Air Temperature (VAT) simulations where the air temperature is allowed to adjust to the imposed radiative cooling and, Constant Air Temperature (CAT) simulations where the surface temperature is tuned to ensure that the atmospheric temperature profile in the domain is constant.
We recover the previously known result that in response to increasing radiative cooling, the area of convection expands rapidly while the intensity of convection does not change. 
We find that this response is explained by the increased boundary-layer variability in simulations with greater radiative cooling, which compensates the decreasing temperature by adding a larger initial velocity close to the cloud-base. We also propose a fundamental scaling of the non-dimensional cumulus mass flux in moist convection which is robust across models of different complexity. We aim to bridge the gap between highly idealised prototypes of moist convection such as  ``Rainy-B\'enard convection" introduced by Vallis et. al. (2019) (https://doi.org/10.1017/jfm.2018.954) and comprehensive cloud-resolving models.