Ensemble of Radiative-Convective Equilibrium Simulations Near the Aggregated and Scattered Boundary

Abstract

An ensemble of 10 radiative-convective equilibrium (RCE) simulations near the sharp transition zone between scattered and aggregated states are examined in a square-domain cloud-resolving model. Surprisingly, the occurrence of self-aggregation is not deterministic near the boundary line of the two states, with six runs reaching aggregated states and four runs returning to scattered states. Spatial autocorrelation length analysis reveals that the development of moisture contrast in the boundary layer (BL) is the key indicator for self-aggregation. To reach aggregated RCE states, a part of the BL needs to be dry and extensive sufficiently to suppress convection triggered by collisions of intruding cold pools. Furthermore, the relation between moisture aggregation and convective organization is elucidated. In a shorter time-scale, convective organization is governed by cold pool dynamics. Meanwhile, large-scale moisture determines the region of active convection for time-scale longer than 2 days.