What favors convective aggregation and why?

Abstract The organization of convection is ubiquitous, but its physical understanding remains limited. One particular type of organization is the spatial self‐aggregation of convection, taking the form of cloud clusters, or tropical cyclones in the presence of rotation. We show that several physical processes can give rise to self‐aggregation and highlight the key features responsible for it, using idealized simulations. Longwave radiative feedbacks yield a “radiative aggregation.” In that case, sufficient spatial variability of radiative cooling rates yields a low‐level circulation, which induces the upgradient energy transport and radiative‐convective instability. Not only do vertically integrated radiative budgets matter but the vertical profile of cooling is also crucial. Convective aggregation is facilitated when downdrafts below clouds are weak (“moisture‐memory aggregation”), and this is sufficient to trigger aggregation in the absence of longwave radiative feedbacks. These results shed some light on the sensitivity of self‐aggregation to various parameters, including resolution or domain size.