Influence of Madden-Julian Oscillation on diurnal precipitation dynamics in the Mentawai Islands: A high-resolution satellite perspective

The Mentawai Islands, located in the eastern Indian Ocean approximately 150 km west of Sumatera, experience precipitation patterns heavily influenced by the eastward propagation of the Madden-Julian Oscillation (MJO). This study investigates the impact of the MJO on local precipitation patterns, with a specific focus on diurnal cycles, during the rainy season (November–March, NDJFM). The analysis is based on Integrated Multi-satellite Retrievals for Global Precipitation Measurement (IMERG) data spanning from 2000 to 2022. It emphasizes diurnal patterns through the lens of precipitation amount (PA), precipitation frequency (PF), and precipitation intensity (PI). The size of the islands strongly shapes the diurnal precipitation patterns during the rainy season. On Siberut, the largest island, two pronounce precipitation peaks are observed: one in the afternoon (15 LST) and another in the early morning (04 LST). Two precipitation peaks were also observed in South Pagai, with an earlier early morning peak (02 LST) and an early afternoon peak (13 LST), exhibiting weaker afternoon peak values compared to those in Siberut. The early afternoon precipitation peak on larger islands suggests a dominant role of local convection in the diurnal precipitation system of the Mentawai Islands. In contrast, the smaller islands—Sipora and North Pagai—exhibit a single precipitation peak at 02 LST, dominated primarily by offshore precipitation propagation from Sumatera. The presence of the Mentawai Islands has been observed to disrupt the offshore propagation of convective systems during nighttime, as indicated by the disruption of PI propagation. However, this disruption becomes negligible when nighttime low-level winds from Sumatera strengthen during MJO phases 2–3. During these enhanced phases, the intensified offshore propagation from Sumatera significantly impacts both the peak values and timings of early morning precipitation in the Mentawai Islands. The enhancement of offshore precipitation propagation during phases 2–3 shifts the peak timing of early morning precipitation in the Mentawai mainland forward by 2 h. This shift in peak timing is particularly pronounced on the smaller islands, where stronger low-level winds associated with the MJO enhance precipitation propagation toward the Mentawai Islands. Understanding the MJO's influence on precipitation patterns in this region is critical for improving weather prediction models and enhancing preparedness for extreme weather events.