Initiation of the Madden-Julian Oscillation: Multiscale Structure Viewpoint

Multiscale interactions play a significant role in the dynamics of the Madden-Julian oscillation (MJO). Most of the rainfall associated with the MJO falls from mesoscale convective systems closely coupled with certain types of synoptic-scale systems, which are destabilized in the planetary-scale environment the MJO provides. How such cooperative interactions are initiated and established over the western Indian Ocean is an essential question to understand the initiation of the MJO, one of the least understood aspects. This study tackles that issue by examining statistical properties of in particular cloud population and cloud morphology using long-term cloudiness datasets with high spatio-temporal resolution. Over 30 significant MJO initiation events were carefully identified for the period 1983-2010 on the basis of empirically-derived spatio-temporal evolution of the MJO. An inspection of time-lapse satellite imagery suggests that westward propagating disturbances which correspond to westward inertio gravity waves are clearly excited in most cases at the initiation stage of the MJO. Their characteristic spatio-temporal scales estimated by virtue of spatio-temporal wavelet analysis and their relation to the planetary-scale environment are discussed. It is hoped that this statistical observational study provides vital information on the initiation of the MJO for both observational and modeling studies under the DYNAMO project.