Boundary-Layer Diabatic Processes, the Virtual Effect, and Convective Self-Aggregation

The MJO has been considered as a form of convective self-aggregation. Here we use a 1D shallow water model and a 2D cloud-resolving model (CRM) to show that boundary-layer diabatic processes are essential for convective self-aggregation in non-rotating atmosphere. We will show that boundary-layer radiative cooling, convective heating, and surface buoyancy flux help convection self-aggregate because they generate available potential energy (APE), which sustains the overturning circulation. We will also show that evaporative cooling in the boundary layer (cold pool) inhibits convective self-aggregation by reducing APE. Both the shallow water model and CRM results suggest that the enhanced virtual effect of water vapor can lead to convective self-aggregation. This study suggests that boundary-layer diabatic processes might be essential to the MJO if it is a form of convective self-aggregation.