Convective self‐aggregation as a two‐regime damped gravity wave

Abstract Convective self‐aggregation is the spontaneous spatial organisation of deep‐convective clouds into a limited region surrounded by drier, convectively inhibited regions, which occurs in many models. We propose a simple, piecewise linear model for self‐aggregation based on primitive equations. In this model, each atmospheric column is in one of two possible thermodynamic regimes, deep convective or convectively inhibited, and the thermodynamics in each regime is linearised. The model simulates aggregated and non‐aggregated steady states and reproduces many properties of self‐aggregation as simulated by kilometre‐resolution models. In particular, it exhibits a hysteresis with multiple, aggregated and non‐aggregated equilibria and a similar sensitivity to convective inhibition, domain size, and boundary‐layer radiative cooling in the dry region as in kilometre‐resolution simulations. These results suggest that a self‐aggregated state can be considered as a simple gravity wave with two phases: one convective and one convectively inhibited.