Effects of the Maritime Continent on Large-Scale Convection Associated with the Madden-Julian Oscillation

Abstract:

The Madden-Julian Oscillation (MJO) is a dominant mode of intraseasonal variability in the tropics. It has wide-ranging impacts on global patterns of precipitation and surface temperature, and it has been suggested that it has an effect on ENSO. Large-scale convection fueling the MJO is initiated over the tropical Indian Ocean and propagates eastward across the Maritime Continent (MC) and into the western Pacific as a pattern of alternating phases of active and suppressed convection. As an eastward-propagating MJO convective event encounters the MC, its nature is altered due to the complex interactions with the landmass and topography as well as the warm coastal ocean. Previous studies have shown strong diurnal cycles over land and ocean, with distinct diurnal maxima of convection during the day and night, respectively. This complex air-sea-land interaction over the MC region and its impact on the large-scale convection and the MJO are still not well understood.

This study aims to improve our understanding of the effects of the MC on the MJO as it propagates eastward from the Indian Ocean to the Pacific. We use the University of Miami Coupled Model (UMCM), a fully coupled atmosphere-wave-ocean model, to investigate the air-sea-land interaction processes and their impact on the large-scale convection associated with MJO. A control simulation of an MJO is carried out first using the DYNAMO observations from 2011 as model verification. To understand the effects of the MC on the MJO convection, coupled model experiments will be conducted by varying the island topography and/or altering the landmass with water surface. Analysis of the coupled model simulations will be compared with satellite observations such as the TRMM precipitation and cloud cluster tracking using hourly IR data. The outcome of this study is expected to provide some insights into important mechanisms that underlie the complex phenomenon.