Role of topography and diurnal cycle of insolation on the MJO in the Maritime Continent

We investigate the influence of topography and the diurnal cycle of insolation on the organization and propagation of the Madden-Julian Oscillation (MJO) across the Maritime Continent (MC). Simulations were conducted using the WRF model for two MJO events, an active MJO event and a weakening MJO event. For each event, three simulations were conducted: control (CTL), removal of topography (NO_TOPO), and removal of diurnal cycle of insolation (NO_DC). In the CTL, the MJO signal is weakened as it crosses the MC, with much of the convection stalling over the major islands of Sumatra and Borneo. However, NO_TOPO and NO_DC simulations show enhanced MJO convection and propagation across the MC. The complex topography of the mountainous islands in the MC induces strong land-sea breeze circulations over the islands, affecting the diurnal cycle of precipitation. Additionally, the topography distorts the coupled Kelvin Rossby wave structure, which is fundamental to the MJO structure and propagation. On the other hand, the diurnal cycle disrupts the smooth propagation of the MJO signal, mainly due to the competition between convection over the islands and the surrounding seas in the MC. While the main convective signal of the MJO propagating through the MC occurs over the seas, the standing convection over the islands, enhanced by the diurnal cycle, competes with convection over the surrounding waters through land-sea breezes and moisture supply. When the diurnal cycle is absent in the simulations, the propagating MJO signal over the MC is strengthened, and convection over the waters dominates that of the islands in the MC. These findings contribute to a better understanding of the factors influencing the behavior of the MJO over the Maritime Continent and its impact on the region's weather patterns.