Objective Diagnostics and the Madden–Julian Oscillation. Part II: Application to Moist Static Energy and Moisture Budgets

Abstract

Abstract Processes controlling moisture variations associated with the MJO are investigated using budgets of moist static energy (MSE) and moisture. To first order, precipitation anomalies are maintained by anomalous large-scale vertical moisture advection, which can be understood through application of a weak temperature gradient balance framework to the MSE budget. Intraseasonal variations in longwave radiative cooling play a crucial role in destabilizing the MJO by enhancing intraseasonal variations in large-scale vertical moisture advection. This enhancement allows the effect of intraseasonal variations in large-scale vertical moisture advection to meet or exceed the effect of intraseasonal variations in net condensation, resulting in a positive feedback between the net effect of these processes and moisture anomalies. Intraseasonal variations in surface latent heat flux (SLHF) enhance this positive feedback, but appear to be insufficient to destabilize the MJO in the absence of radiative feedbacks. The effect an ensemble cloud population has on large-scale moisture is investigated using fields where only high-frequency variability has been removed. During the enhanced phase, approximately 85% of the moisture removed by net condensation is resupplied by the large-scale vertical moisture advection associated with apparent heating by microphysical processes and subgrid-scale vertical fluxes of dry static energy. This suggests that a relatively large increase in net condensation could be supported by a relatively small anomalous moisture source, even in the absence of radiative feedbacks. These results highlight the importance of process-oriented assessment of MJO-like variability within models, and suggest that a weak temperature gradient (WTG) balance framework may be used to identify destabilization mechanisms, thereby distinguishing between MJO-like variability of fundamentally different character.