Extratropical Convective Precursors to Initiation of MJO Convection Over the Indian Ocean

Prior to the development of Madden-Julian Oscillation deep convection over the Indian Ocean, anomalously enhanced convection usually forms in the extratropics over Africa, the western Indian Ocean, and southwest Asia with corresponding upper-tropospheric enhanced moisture. Though previous work has attributed these signals to Rossby waves forced by MJO suppressed convection over the Indian Ocean, the progression of these signals and the relationship between them and the equatorial MJO could help to provide an improved understanding of MJO convective initiation over the Indian Ocean. In order to resolve these specific convective features better than an MJO index based on global equatorial convection and circulation, an index using the principal components of the leading two time-extended 40S-40N latitudinal EOFs of 20-100 day-filtered outgoing longwave radiation anomalies averaged over 20-70E has been created. Though this region is not typically thought of as a center of strong MJO convective variability, global composite fields created with the index show eastward propagation along the equator, consistent with MJO convection, comparable to composites based on widely used MJO indices. Results show that the targeted equatorward-moving convective and moisture signals over Africa may constitute important precursors of MJO convective events over the Indian Ocean.