Modulation of the Diurnal Cycle of Convection over the Maritime Continent by the Madden–Julian Oscillation

The Madden-Julian Oscillation (MJO) is the dominant mode of intraseasonal variability in the tropics. Large-scale convection fueling the MJO is initiated over the tropical Indian Ocean (IO) and propagates eastward across the Maritime Continent (MC) and into the western Pacific as a pattern of alternating phases of active and suppressed convection. The MJO’s convective initiation and eastward propagation over the tropical IO and MC are not well understood. Previous studies have documented the MC barrier effect, showing that 40-50% of all MJO events do not pass through the MC and into the western Pacific, which is attributed to the presence of significant topography and the established diurnal cycle (DC) of convection over it. The strong diurnal cycle over the islands and coastal waters is climatologically characterized by an afternoon precipitation maximum over land and high terrain, and an early morning maximum over water and mountain valley areas. As the MJO is passing over the MC, it modulates the DC of convection, and that may affect the propagation of the MJO in return.

In this study, we examine the changes in the DC of convection over the MC that coincide with active and suppressed phases of the MJO. MJO events in are identified using the large-scale precipitation (LPT) method that locally tracks large eastward-propagating areas of intense sustained precipitation and their evolution in both space and time. LPT tracking is be performed on the Global Precipitation Mission (GPM) IMERG high resolution dataset (0.1°, 30-minute) spanning from March 2014 (or earlier, if data become available) until December 2017. In addition, we analyze the climatological DC of precipitation over the MC in the same dataset, and then evaluate the changes in the DC that coincide with convectively active and suppressed phases of the MJO over the area. Preliminary results show that the passage of the MJO modifies the DC of convection over the MC, though land and ocean areas within the MC experience its passage in different ways; the night-time of convection over water is enhanced more than the day-time convection over land. Results of more in-depth analysis will be presented at the meeting.