Analysis of the 10–20-Day Intraseasonal Oscillation in the Indian Ocean Using Surface Winds from Composite Satellite Data

The 10–20-day mode of surface winds is examined in the Indian Ocean, with special reference to the Arabian Sea, the Bay of Bengal, and the equatorial Indian Ocean during a strong (1994), weak (2002), and normal (1995) Indian summer monsoon. The winds are from the Cross Calibrated Multi-Platform (CCMP) gridded wind product version 2.0. Results indicate the 10–20-day mode of latitudinally averaged surface winds have zonal propagation in the western Indian Ocean (west of 75°E) and the signal appears stationary in the eastern Indian Ocean (east of 75°E) during May through September. The meridional propagation of the 10–20-day mode of longitudinally averaged surface winds appears weak during summer monsoon periods. The 10–20-day mode of surface winds in the Arabian Sea and the Bay of Bengal is more energetic than in the equatorial Indian Ocean. The signal of the 10–20-day mode appears more robust during a strong monsoon than during a weak monsoon in the Arabian Sea; however, no significant difference is found in the Bay of Bengal and equatorial Indian Ocean between strong and weak monsoons. Ensemble empirical mode decomposition (EEMD) analysis is used on a time series from the Arabian Sea to create an index for the 10–20-day mode in surface winds. Using this index, 75 cases of 15-phase 10–20-day events are identified and used to create composites of surface winds. Through these composites, a positive surface wind anomaly is found to appear at 60°E, centered on 15°S, and propagate zonally eastward to 90°E before reflecting back to propagate westward and then disperse off the coast of Madagascar. It is proposed that this oscillating positive wind anomaly is a feature of the southernmost cell of the 10–20-day convective double-cell structure that has extended farther south into the southern Indian Ocean and that this mode connects the Arabian Sea and southern Indian Ocean through the Somali Jet and surface winds.