The MJO-Kelvin Wave Transition

As the Madden-Julian oscillation (MJO) moves eastward from the Indian to the Pacific ocean, it typically accelerates, becomes less strongly coupled to convection, and becomes more similar to a dry Kelvin wave. This transition is analyzed using observations of outgoing longwave radiation and ERA Interim reanalyses of surface pressure and 850 hPa zonal wind. Two individual example events as well as composites are shown. The transitions are well defined, with distinct disturbances on either side of the transition whose identities as MJO or Kelvin waves are clear. In some cases there appears to be a pre-existing Kelvin wave passing through the MJO from the west to the east, but this feature is not apparent in the composites. The transitions occur at different longitudes in different events, over a wide range from the eastern Indian to the central Pacific oceans. Because the character of the disturbances changes so much at the transition, a successful MJO forecast must include, explicitly or implicitly, a prediction of at what longitude this transition will occur.