An Indo-Pacific alternation of the boreal winter MJO

During boreal winters, perturbations of the convection by the Madden-Julian Oscillation (MJO) peak over three basins: the eastern Indian Ocean (IO), the south of the Maritime Continent (MC) and the western Pacific Ocean (PO). We use the observed Outgoing Longwave Radiation (OLR) to identify and characterize all wintertime MJO events between 1979 and 2010. There is a large event-to-event variability with some MJO well resembling the canonical MJO and some with a convective perturbation peaking over a single basin. However, many events may be identified as either West MJO (convection peaking over IO and MC) or East MJO (convection peaking over PO and MC). We quantify this alternation between West and East MJO by an Indo-Pacific Index (IPI). The IPI reflects different planetary-scale perturbations of the MJO with an interannual variability partly related to ENSO. Low-level wind perturbations of West and East MJO closely follow the basin-scale convective perturbation consistently with a Gill-type response. This wind response is non-linear and leads to different impacts of East and West MJO on the average large-scale circulation.