On the dynamics of unsaturated atmospheres in a simple model of moist convection*

Convection represents a fundamental process in the atmosphere, and clouds represent a major uncertainy in climate modeling. These phenomena are coupled by the latent heat of condensation: moisture is not merely a passive tracer in convective dynamics but a key source of buoyancy. Here, we present linear and non-linear results using the simplified, Boussinesq "Rainy-Benard" model with the aim of drawing on the vast reservoir of knowledge for Rayleigh-Benard convection to elucidate systems with Earth-like condensation physics. We focus on systems that transition from unsaturated conditions in the lower atmosphere to saturated conditions aloft. At modest Rayleigh number of order 10¹²-10¹⁴, systems that are stable to dry convection but destabilized by condensation show a propensity to spontaneously form layers in both two- and three-dimensions. The strength and non-linear dynamics of these layers depend on the both the Rayleigh number and the specific latent heat released by the condensing fluid.