Convection On the Edge

Abstract

AbstractDeep convection over tropical oceans often appears intensified at the edge of convectively active regions, both in idealized studies and in observations. This edge intensification of convection is studied in detail here, using the steady state of a radiative‐convective equilibrium study, marked by a single convective cluster with deep convection intensified at the edge of this cluster. The cause for edge intensification and its dependence on the cluster area is investigated by comparing the spatial distribution of deep convection to different variables known to be important for convection. Analysis of the simulation suggests that the edge is marked by an increased probability for the triggering of convection rather than by stronger updrafts. In particular, while the edge of the moist region is not thermodynamically more favorable, we find strong surface convergence and therefore dynamical lifting at this edge. The surface convergence is shown to result from two opposing flows. On the one hand, there is, as expected from previous radiative‐convective equilibrium simulations, a low‐level inflow directed toward the moist region. On the other hand, there is a positive density anomaly at the surface which is the result of continuously forming cold pools within the convectively active region, creating a super‐cold‐pool. As the velocity of the low‐level inflow approximately matches the potential propagation speed of the super‐cold‐pool boundary, these opposing flows explain the presence of strong convergence at the edge of this region. Whether the resulting lifting induces the formation of deep convection is shown to depend on the large‐scale instability.