Ocean Feedbacks and Atmospheric Precursor Signals Associated with Eastward-propagating and Eastward-decaying Tropical Intraseasonal Convection

Abstract:

Nature provides examples of eastward-propagating events that do (MJO) and do not (eastward-decaying, or ED) propagate across the Maritime Continent. Each type of event is observed during positive, neutral, and negative phases of ENSO and the Indian Ocean Dipole (IOD), but we limit our analysis to years with only weak or neutral interannual signals.

MJO events can be subdivided into “small” and “big” events, as defined by the details of their OLR signatures; both small and big MJO events can initiate as primary or successive events. Big MJO events exhibit precursor signals and circulations that promote MJO initiation over a variety of Indian Ocean background states. Small MJO and ED events lack one or more of these precursor signals, but are frequently distinguished by their background upper ocean state: small MJO events are associated with downwelling oceanic Kelvin and equatorial Rossby waves (which promote SST warming), while ED events are associated with upwelling Rossby waves (which limit SST warming).

In this study I will explore the relative contributions of atmospheric circulations and ocean feedbacks to each type of event. I will also demonstrate how this kind of analysis can shed light on MJO events simulated by models.