Gross Moist Stability Assessment: Convective Amplification and Decay

We analyze moist static energy (MSE) and dry static energy (DSE) budgets from satellite-based data sets to investigate convective amplification/decay mechanisms over the tropical ocean. The gross moist stability (GMS), which represents efficiency of MSE export by large-scale circulations associated with the convection, is examined, together with two related quantities, the critical GMS (a ratio of diabatic MSE budget terms to the convective intensity) and the drying efficiency (a version of the effective GMS; GMS minus critical GMS), which we coined. We show that convection over the tropical ocean would most likely (>80 %) amplify/decay when there is a negative/positive drying efficiency (or effective GMS).

Utilizing the amplification-decay property, we propose a new diagnostic framework on which convective events are plotted on the column-MSE-flux-divergence vs. column-DSE-flux-divergence plane. On this plane, convection in the amplifying phase appears below some critical line (or critical GMS line) while convection in the decaying phase appears above the critical GMS line, and each convective life-cycle can be viewed as a fluctuation of a data point around the critical GMS line. This diagnostic framework becomes particularly useful when analyzing convective life-cycles using satellite-based data sets which rarely give us continuous time-series. Using that diagnostic framework, we investigate potential mechanisms of convective amplification and decay over the tropical ocean in satellite data.