The Interaction of Eastward Propagating Equatorial Modes with the Maritime Continent

We examine the processes that contribute to blocking of the eastward propagating, equatorial modes by the Maritime Continent . The recent study by Baranowski et al. (2015) have shown that the propagation of Kelvin waves through the Maritime continent is strongly influenced by the interaction of the waves with the diurnal cycle of convection which can either amplify or suppress the convective forcing of the wave, suggesting that in order for the wave to cross the Maritime Continent it has to be in phase with the local land convection. Another possible mechanism through which the Maritime Continent can influence approaching Kevin waves and the MJO is the interaction between the eastward propagating waves and the cyclonic disturbances generated by the lee vortices at the tips of Sumatra. Both of these mechanisms can be misrepresented in dynamical models and can lead to MJO “predictability barrier” in this region. These equatorial modes are examined in Navy model forecasts of DYNAMO MJOs and idealized simulations. While both NAVGEM and COAMPS appear to predict the MJO approach to the Maritime Continent, the propagation is often too slow, and westward propagating cyclonic vortices in the eastern Indian Ocean tend to develop in many simulations. We examine the contribution of Sumatra lee vortices and Maritime Continent diurnal convective variability to this process.