Characteristics of diurnal condensational heating at the Western Maritime Continent during MJO eastward propagation

The Maritime Continent (MC) is a unique region with a pronounced diurnal cycle and the strong impact of the Madden–Julian Oscillation (MJO). How and to what extent eastward propagating MJOs influence the diurnal cycle of the condensational heating at the Western Maritime Continent (WMC) during boreal winter is investigated with observational and re-analysis data. The diurnal heating field shows distinctive vertical profiles and peak time in the land and the surrounding ocean, with the former (latter) peaking in the lower troposphere near 700 hPa and in the early morning (near the surface and in the late afternoon). The diurnal condensational heating at WMC is enhanced when MJO is locates in the Indian Ocean (IO) and weakened when MJO moves to MC and Western Pacific (WP). Through the diagnosis of the moisture equation, it is found that the MJO-dependent change of the diurnal heating is predominantly contributed by anomalous vertical advection of the background moisture by the diurnal vertical velocity field. The amplitude of the diurnal vertical velocity field is significantly strengthened (weakened) when MJO is located at IO (MC and WP), due to the fact that MJO exhibits a tilted vertical structure with increased low-level moisture in front of MJO convection. It is the MJO induced background moisture increase that favors the strengthening of the diurnal cycle activity through moisture-convection-circulation feedback.