A Westward Propagating Intraseasonal Mode over the Western Pacific

Intraseasonal variability has been a central topic of interest in the climate modeling community. The main player on such timescales is the Madden-Julian oscillation (MJO), which is characterized by slow eastward propagation along the equator, planetary spatial scales, and a peak in amplitude during boreal winter. In this study, we illustrate that a westward propagating mode of intraseasonal variability prevails over the western Pacific during boreal winter as the second leading mode in addition to the eastward propagating MJO. Similar to the MJO, the westward propagating mode propagates slowly and is also of a large spatial scale. In this presentation, comprehensive characteristics as well as the three-dimensional vertical structure of the westward propagating mode will be presented. A budget analysis of the column-integrated moist static energy will also be illustrated, wherein fundamental differences in physics for the eastward propagating MJO and this westward propagating intraseasonal mode exist.