Realistic initiation and dynamics of the1 Madden-Julian Oscillation in a coarse resolution2

The main mechanisms for the initiation and propagation of the Madden-4 Julian Oscillation (MJO) are still widely debated. The capacity of operational5 global climate models (GCMs) to correctly simulate the MJO is hindered by6 the inadequacy of the underlying cumulus parameterizations. Here, we show7 that a coarse resolution GCM, coupled to a simple multicloud model param-8 eterization mimicking the observed dynamics and physical structure of or-9 ganized tropical convection, simulates the MJO in an idealized setting of an10 aquaplanet without ocean dynamics. We impose a fixed non-homogeneous11 sea surface temperature replicating the Indian Ocean/Western Pacific warm12 pool. This results in a succession of MJOs with realistic phase speed, am-13 plitude, and physical structure. Each MJO event is initiated at a somewhat14 random location over the warm pool and dies sometimes near the eastern15 boundary of the warm pool, and sometimes at a random location way be-16 yond the warm pool. Also occasionally the MJO events stall at the center17 of maximum heating. This is reminiscent of the fact that in nature some MJOs18 stall over the maritime continent while others reach the central Pacific Ocean19 and beyond. The initiation mechanism in the model is believed to be a com-20 bination of persistent intermittent convective events interacting with observed21 large scale flow patterns and internal tropical dynamics. The large scale flow22 patterns are associated with planetary scale dry Kelvin waves that are trig-23 gered by preceding MJO events and circle the globe while congestus cloud2