Role of the Diurnal Cycle of Land Convection in the Barrier Effect on the MJO by the Maritime Continent

Possible effects of the diurnal cycle in land convection on the eastward propagation of MJO over the Indo-Pacific Maritime Continent (MC) during the boreal winter were investigated using high-resolution precipitation data. Inidividual MJO events were identified using a precipitation-tracking method and classified into two groups: those propagating across the MC (MJO-C) and those blocked by the MC (MJO-B). Before an MJO convection center propagates into the MC, rain is more over land in the MC (“vanguard precipitation”) for MJO-C than MJO-B and most rain over land comes from diurnal convection. Once the MJO convection center enters the MC, the diurnal cycle over land is significantly weaker for MJO-C than MJO-B, possibly because higher surface soil moisture due to vanguard precipitation tend to suppress diurnal convection over land. This result provides observational evidence that fill a gap in a hypothesized chain of actions in which the diurnal cycle of land convection plays an active role in the barrier effect on the eastward propagation of MJO over the MC. Remaining gaps in this hypothesis are discussed.