Why does the MJO detour the Maritime Continent during austral summer?

Abstract

Eastward propagation of the Madden-Julian Oscillation (MJO) detours the Maritime Continent (MC) region southward during austral summer, exhibiting enhanced convective activity preferentially in the southern part of the MC area with much weaker anomalies in the central MC area. Column-integrated moist static energy budget of the MJO is analyzed to understand the processes responsible for the MJO detouring. Results show that zonal and meridional moisture advection is the essential process to the MJO detouring, causing the difference between the southern and central MC regions in the moisture recharge before and during the MJO onset. Further analysis reveals that moisture advection by MJO perturbation winds acting upon the background moisture gradient has the dominant contribution to the regional contrast between the central and southern MC areas. The zonal moisture advection is greater in the southern MC region because the zonal gradient of the background moisture field is much steeper in the southern MC area than in the central MC area. The onset of the Australian monsoon in austral summer contributes to the establishment of the sharp zonal moisture gradient in the southern MC region. The meridional moisture advection is weaker in the central MC area because meridional wind anomalies associated with the MJO vary regionally, presumably through interactions with the topography and land-sea contrast.