Relative Roles of Preconditioning Moistening and Global Circumnavigating Mode on the MJO Convective Initiation During DYNAMO

The relative importance of preconditioning moistening and global circumnavigating mode in the convective initiation of the October 2011 Madden–Julian Oscillation (MJO) event observed during the Dynamics of the Madden–Julian Oscillation (DYNAMO) field campaign is investigated using a series of convection-permitting regional model simulations. It is demonstrated that the MJO convective initiation is largely controlled by the global circumnavigating mode at the intraseasonal scales. Rapid moistening closely related to this eastward propagating mode a few days prior to the MJO active phase is crucial to the initiation of deep convection and enhanced rainfall. This moistening process nevertheless cannot be accurately described by the “discharge-recharge” hypothesis, which speculates the importance a gradual moisture buildup over an approximately 2-week period leading to the arrival of the active MJO phase.