Topographic Influences on Diurnally Driven MJO Rainfall Over the Maritime Continent

Abstract

AbstractThis work investigates impacts of the Madden‐Julian Oscillation (MJO) on the daily and diurnal rainfall over the Maritime Continent, with emphasis on the influences of topography over Sumatra, Borneo and New Guinea. Eighty‐nine MJO events were identified during 2001–2019 using IMERG satellite data. Daily and diurnal rainfall maxima on the east side of topography lag the west side as the MJO passes. In addition, the island vanguard (pre‐MJO) rain is more convective, while the island rearguard (behind the main MJO body) rain is more stratiform. The timing and magnitude of diurnal rainfall is defined using the maximum hourly rain rate instead of the first diurnal harmonic to avoid smoothing. While a single sharp peak is observed over the mountains around 19 LT, a much broader delayed peak occurs over land to the west of topography and two peaks are observed over land to the east of topography at 15 and 2 LT. Rain peaks offshore from 3 to 7 LT. Cluster analysis shows that the afternoon and nighttime rainfall peaks are highest before the MJO arrives, then gradually decrease and become earlier on the west side of the topography, whereas the afternoon (nighttime) peak east of the topography is enhanced before (after) the MJO arrives. The contrasting east‐west features can be attributed to topographic influences on the moisture flux convergence of the mean column moisture by MJO‐induced winds. The MJO wind modulation of diurnal rainfall over most of the open ocean areas is insignificant.