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

Possible effects of the diurnal cycle in land convection on propagation of the Madden–Julian Oscillation over the Indo‐Pacific Maritime Continent (MC) were investigated using satellite observations. Four features distinguishable from their respective climatology are uniquely associated with MJO events that cross the MC: strong precipitation over land as their convection centers approach the MC, subsequent increased soil moisture, reduced diurnal amplitude of land convection, and the dominance of precipitation over water by nondiurnal convection as their convection centers move over the MC. These results provide observational evidence for a proposed MAritime Continent Convective diurnal Cycle mechanism in which the diurnal cycle in land convection acts as an intrinsic barrier effect on MJO propagation over the MC. Plain Language Summary By influencing global weather and climate, the Madden‐Julian Oscillation (MJO) plays a central role in intraseasonal prediction. But when it propagates over the Indo‐Pacific Maritime Continent (MC), the MJO often weakens and sometimes breaks down and ceases to exist. This is known as the barrier effect of the MC. The reason for this barrier effect is not well understood. Through diagnosing satellite data of precipitation and soil moisture, this study provides observational evidence for several steps in a MAritime Continent Convective diurnal Cycle mechanism, in which the diurnal cycle in land convection acts as an intrinsic barrier effect that must be overcome for the MJO to propagate through the MC. The observations show that increased soil moisture reduces the amplitude of diurnal convection over land, allowing convective systems over water of the MC to develop and carry MJO signals through the MC. Key Points MJO precipitation over the Maritime Continent (MC) is dominated by diurnal convection over land and nondiurnal convection over water Climatological diurnal land convection acts as an intrinsic barrier effect that must be overcome for the MJO to propagate through the MC Increased soil moisture helps reduce the diurnal amplitude of land convection and overcome the barrier effect