Role of Topography and Diurnal Cycle of Insolation on the MJO-Associated Precipitation in the Maritime Continent

We explore the influence of topography, diurnal cycle of insolation, and their interactions on the Madden-Julian Oscillation (MJO)-associated convection in the Maritime Continent (MC) using reginoal model simulations. Two MJO events were considered, a weakening MJO event that weaken in the MC compared to when it entered the MC. and an active MJO event that did not weaken. For each event, four simulations were conducted: control (CTL), removal of topography (TOPO), removal of diurnal cycle of insolation (DC), and removal of topography and diurnal cycle of insolation (TOPO_DC). The CTL simulations compare reasonably well against observations. The TOPO and DC simulations demonstrate an amplified and distinct propagation of MJO convection across the MC compared to CTL based on large-scale precipitation tracking method. The intricate topography of the mountainous islands within the MC influences land-sea breeze circulations over these islands, thereby strengthening the diurnal cycle of precipitation. The diurnal cycle in precipitation disrupts the smooth progression of the MJO signal, primarily due to the competition between convection occurring over the islands and that over the surrounding seas in the MC. While the principal convective signal of the MJO traversing the MC predominantly occurs over the seas, the stationary convection over the islands, intensified by the diurnal cycle, competes via land-sea breezes and moisture supply. The DC simulation strengthens the propagating MJO signal over the MC, resulting in dominant convection over the waters rather than the islands within the MC. Role of the interactions between the topography and diurnal cycle of insolation on MJO convection is also discussed.