On Diagnostic Applications of Gross Moist Stability

Abstract:

We analyze moist static energy (MSE) budgets derived primarily based on the TRMM Microwave Imager (TMI) and the Objectively Analyzed Air-sea Fluxes (OA Fluxes) datasets to investigate convective amplification/decay mechanisms over the tropical ocean. The gross moist stability (GMS), which represents MSE export efficiency by large-scale circulations associated with the convection, is studied, together with two relevant quantities, critical GMS (a ratio of diabatic forcing to the convective intensity) and drying efficiency (a version of the effective GMS; GMS minus critical GMS), which we coined. We show that convection over the tropical ocean intensifies/decays via negative/positive drying efficiency (or effective GMS). We propose a new composite method which is taken on values of the drying efficiency, and illustrate that that composite method is particularly useful for diagnosing convective amplification/decay. The proposed composite space provides us with a new interpretation of convective life-cycles with high frequencies (on a-couple-day time-scales), and furthermore, clarifies the relationship between the GMS of slowly changing, large-scale phenomena and the vertical motion profiles of higher-frequency convective disturbances (such as mesoscale convective systems and tropical waves). We also analyze the ERA-Interim dataset to compare the results from the satellite-based products and the re-analysis datasets.