Thoughts on the Basic Physics of the MJO

At a recent meeting on the MJO it was mentioned that we still lack a fundamental picture of the physical mechanisms underlying this phenomenon. We have gone back to basics in order to see whether recent and not-so-recent hypotheses about the MJO can be combined to produce a coherent picture that explains its salient features. In particular, we look at a model invoking linear WISHE combined with moisture mode dynamics. The arguments against this model are three-fold: First, consistent mean easterlies do not exist uniformly across the MJO domain, making linear WISHE questionable. Second, the MJO is arguably highly nonlinear. Third, vorticity dynamics play a much stronger role in the MJO than the linear model would suggest. In spite of these arguments, this simplified model explains the large spatial scale of the MJO, the mechanism for eastward propagation, and its observed group velocity. Why this is so is the subject of current investigation.