Propagating and Nonpropagating MJO Events over Maritime Continent

The observed outgoing longwave radiation (OLR) and ERA-Interim data during 1979-2008 (from November to April) were analyzed to reveal fundamental differences between eastward-propagating (EP) and nonpropagating (NP) MJO events across the Maritime Continent (MC). It was found that when the maximum MJO convection arrives near 120 degrees E, a positive (negative) moisture tendency lies in its east for the EP (NP) cases. In NP cases, there are clearly detectable westward-propagating Rossby wave-type dry signals over the equatorial central-western Pacific. The dry Rossby-wave signal may hinder the development and eastward propagation of new MJO convection. A moisture budget analysis shows that the positive tendency of specific humidity in the EP composite is mainly attributed to the advection of the mean moisture by an intraseasonal ascending motion anomaly, whereas the negative tendency in the NP composite arises from the advection of anomalous dry air by the mean easterly and the advection of the mean moisture by the anomalous easterly. The EP cases were further separated into a group with and a group without a clear suppressed convective phase of OLR to the east of the MJO convection, where the column-integrated moisture anomaly is negative and positive, respectively. Nevertheless, the column-integrated anomalous moisture tendency is always positive in both groups that induce MJO convection crossing the MC. Such positive tendencies are caused by different processes. In the former (latter), it is mainly attributed to anomalous horizontal advections associated with eddy moisture transport and mean moisture advection by intraseasonal meridional wind (mean moisture advection by anomalous vertical velocity).