Diversity of MJO Initiations Over the Indian Ocean Basin

Abstract

The Indian Ocean (IO) basin is often identified as the primary location for the initiation of Madden Julian Oscillations (MJO). This study investigates the diversity of MJO initiations within the IO basin focusing on the influence of background state and the preconditioning processes which drive the convection initiations. While the western equatorial Indian Ocean (WEIO) emerges as the most preferred location for initiation, ∼40% of MJO initiations are observed over the eastern equatorial Indian Ocean (EEIO) and they exhibit stronger convective amplitudes compared to the western counterpart. The IO sea surface temperature background state is observed to influence the frequency of occurrence of initiations over the two domains only during boreal summer. Investigation of the preconditioning associated with winter MJO initiations reveals a gradual destabilization over the WEIO, dominated using shallow convective processes and gradual moistening of the lower troposphere. A more rapid and stronger destabilization is observed over the EEIO and the difference is attributed to the moist dynamics in the planetary boundary layer (PBL). PBL moisture budget analysis reveals that while the moistening over EEIO results from the competing effects of horizontal and vertical advection processes, horizontal advection together with cloud evaporative processes drives the moistening of the PBL over the WEIO. A stronger zonal gradient in the mean moisture field and the larger amplitude Rossby response to the suppressed state over the Maritime Continent contribute to strong horizontal advection of moisture over the EEIO, which leads to the rapid destabilization and stronger convection development over the domain.