Moist static energy and the MJO

A range of evidence suggests that the MJO is a) not a Kelvin wave; b) better simulated in models in which deep convection is sensitive to moisture; c) stronger over ocean than land, indicating a dependence on the total surface heat flux, which in turn suggests that surface turbulent fluxes and radiative cooling both help to modulate the convection associated with the MJO. This evidence leads to the hypothesis that the MJO is a “moisture mode”. We use this term to mean a mode of variability that, in mathematical models, depends inherently on a prognostic moisture equation, and that is best viewed from the point of view of the budget of moist static energy or moist entropy.

I will present recent observational, numerical and theoretical work examining the moist static energy budget of the MJO. Results will be presented from the DYNAMO field campaign observations, cloud resolving simulations with parameterized large-scale dynamics, GCM simulations, and an idealized semi-empirical theoretical model. The essential messages are: 1) cloud-radiative feedbacks are essential to drive the MJO, and 2) horizontal advection is essential to its eastward propagation, especially in the region between the western Indian ocean and westernmost Pacific.