Sack Lunch Seminar (SLS)

Abstract:

The Madden–Julian oscillation (MJO) is the dominant mode of intraseasonal variability (50-60 day recurrence interval) in the tropics. It is a planetary-scale pattern of tropical rainfall and zonal wind anomaly that drifts slowly eastward from the Indian Ocean into the Pacific and past the International Dateline. Until recently, models have ignored the small-scale, high-frequency structures that are imbedded in the MJO, but now these structures are getting more attention. Here we employ the shallow water equations with convection parameterized as a triggered mass source (time constant less than half a day). The convection events excite quasi-standing inertia-gravity (IG) waves that trigger more convection. The standing waves are a superposition of eastward and westward IG waves, but the former propagate slightly faster than the latter, causing the pattern to drift slowly eastward, as observed. Thus we propose that the MJO is an interference pattern of eastward and westward IG waves. It has been difficult to prove or disprove this hypothesis with observations, but I will present a progress report on these efforts.