Novel MJO Diagnostics Based on WTG Theory and Application to Models and Reanalysis Datasets

Abstract:

A large and growing body of research over the last decade and a half has applied weak temperature gradient (WTG) theory to understand the dynamics of the Madden-Julian oscillation (MJO). Following from this recent literature, this talk will first describe the development of novel process-oriented MJO diagnostics based on WTG assumptions that can be used to diagnose the dominant processes responsible for MJO destabilization, propagation, and initiation. These diagnostics make use of the synoptic-scale balance of diabatic heating by adiabatic cooling in the tropics under small Coriolis force, which holds extremely well on MJO timescales. Next, these diagnostics will be applied to the ERA-I reanalysis dataset and several models including the superparameterized CCSM (SP-CCSM), NCAR CESM, and regional convection-permitting simulations for the November 2011 MJO event during the DYNAMO field campaign. We will show through examination of column moistening processes associated with condensation and vertical moisture advection that radiative feedbacks are necessary for understanding MJO destabilization in both reanalysis datasets and SP-CCSM. Interestingly, these diagnostics also show that horizontal moisture advection in SP-CCSM appears necessary for understanding the tilted horizontal moisture structures in the model, which traditionally have been thought to be primarily due to shallow convective moistening. Finally, diagnostics of column processes from SP-CCSM and NCAR CESM will be contrasted, and provide insight into why SP-CCSM produces a robust MJO, while the CESM does not.