The MJO Skeleton Model: Stochastic Dynamics, Comparison with Observations, and Development of New MJO Indices (Invited Presentation)

The Madden–Julian Oscillation (MJO) skeleton model is a nonlinear oscillator model that predicts the slow eastward propagation speed and quadrupole vortex structure as in the MJO in nature. Here we present further results for the model's use in the identification and potentially the prediction of the MJO: (i) detailed statistical comparisons between the stochastic skeleton model and observed statistics of the MJO in nature and (ii) new MJO indices based on MJO skeleton theory. In the statistical comparisons, for example, it is shown that the model simulations reproduce the climatological mean convective activity well and the climatological variance reasonably well for such a simple model. In the direction of identification of the MJO, a hierarchy of MJO Skeleton Indices is presented, ranging from (I) a spatiotemporal index MJOS(x,t) with detailed longitudinal variations in the MJO amplitude to (II) simple two-degree-of-freedom indices for the MJO's amplitude and phase. No temporal filtering nor empirical orthogonal functions (EOFs) are used in these indices. The indices are illustrated with case studies from observational data, and they could also be used for analyzing climate model data.