Modulation of Diurnal Rainfall Cycle by the Madden-Julian Oscillation Based on One-Year Continuous Observations with a Meteorological Radar in West Sumatera

Abstract

One-year meteorological radar observations (from November 2006 to October 2007) over a region from the west coast of central Sumatera (Sumatra) through the Mentawai Strait (about 130-km width) to Siberut Island were analyzed, and modulation of rainfall diurnal cycle (DC) in the region by the Madden-Julian oscillation (MJO) was studied. The DC peaked in the afternoon over Sumatera and Siberut islands, and in the nighttime/early morning over Mentawai Strait between the islands. Over the strait, offshore (westward) migration of the DC peak was distinct when the MJO active phase was propagating eastward over the Indian Ocean, whereas the migration was indistinct after the active phase passed over Sumatera. When the MJO active phase was propagating eastward over the eastern Indian Ocean, the DC was amplified, and daily rainfall maximum tended to appear over western Sumatera including the strait. The DC peak originating from Sumatera reached Siberut, and the DC over Siberut had an additional, stronger rainfall peak after midnight.