New Perspectives of the MJO from Tracking Its Precipitation

A recently developed and refined method of tracking eastward motion of equatorial precipitation anomalies has led to new perspectives of the MJO. This method identifies individual MJO events and their characteristics, such as starting and ending time and longitudes, propagation speed and range, strength, life span, and intervals between two adjacent events. Results from the tracking method demonstrate that most MJO events form over the Indian Ocean. Of all MJO events that form over the Indian Ocean, 50% fail to propagate through the Indo-Pacific Maritime Continent (MC), hence the barrier effect of the MJO. The most striking difference between MJO events that propagate through the MC and those that do not is their precipitation distributions over land vs. oceans in the MC region. MJO events propagate through the MC only if their convection over the MC seas dominates convection over land. When the MJO tracking method is applied to global model simulations, it reveals that, in contrast to the previous perception of only few global model being able to produce the MJO, all of them can. The difference is in the occurrence frequency of the MJO they produced. Models that show statistical MJO signals produce MJO events relatively frequently whereas models that do not show statistical MJO signals produce MJO event infrequently. It is argued that the reason for the difference is in the background state a model produces vs. the background state required for the model to produce the MJO. They are not necessary the same.