Intraseasonal equatorial Kelvin waves in the Indian Ocean and their propagation into the Indonesian Seas

Michael J McPhaden, NOAA Seattle, Seattle, WA, United States and Kandaga Pujiana, CIMAS NOAA/AOML, Seattle, United States; Bandung Institute of Technology, Bandung, Indonesia
Intraseasonal oceanic variations in the Indian Ocean are prominent mode of variability affecting the evolution of the Indian Ocean Dipole, the semi-annual Wyrtki jets, and the Indonesian Throughflow. This presentation highlights the structure and propagation of wind forced intraseasonal Kelvin waves along the equator in the Indian Ocean and their penetration into the Indonesia Seas. For this purpose, we use unique, multi-year (2004-2016) moored velocity time series data from the equatorial eastern and central Indian Ocean, moored time series from Lombok, Makassar, and Ombai Straits, satellite altimetry, and oceanic and atmospheric analysis products. The waves are generated along the equator by the Madden-Julian Oscillation with periods of roughly 20-90 days. Phase propagates eastward and upward, consistent with Kelvin waves that radiate energy downward as they travel along the equator. Meridional structures in zonal velocity and sea level are Gaussian with a decay scale equivalent to that of a second baroclinic mode. As the modes reach the coast of Sumatra, they partially reflect into Rossby waves, but some energy radiates poleward. Southward propagating energy along the coast of Java can be traced through Lombok Strait into Makassar Strait and later to Ombai Strait at lags of 2-3 weeks. The implications of these results for understanding variability in the Indian Ocean and its connectivity with the Indonesian Seas will be discussed.