National Institute Of Oceanography( NIO ) - Intraseasonal response of the northern Indian Ocean coastal waveguide to the Madden-Julian Oscillation

Intraseasonal response of the northern Indian Ocean coastal waveguide to the Madden-Julian Oscillation

A new observational record of upper-ocean currents at 15°N on the western coast of India is dominated by intraseasonal (55'110 day) variations of alongshore currents, whereas sea level at the same location has a clear seasonal signal. These observations can be interpreted within the framework of linear wave theory. At 15°N, the minimum period for planetary waves is ~90 day, meaning that intraseasonal energy is largely trapped at the coast in the form of poleward-propagating Kelvin waves, while lower-frequency signals associated with the annual cycle can radiate offshore as planetary waves. This dynamical difference results in a steeper offshore slope of sea level at intraseasonal timescale, and thus stronger geostrophic alongshore currents. A consequence is that the alongshore currents are in-phase with intraseasonally-filtered sea level near the coast, and a gridded satellite product is shown to reproduce the current variations reasonably well. The intraseasonal current variations along the west coast of India are part of basin-scale sea-level fluctuations of the Northern Indian Ocean equatorial and coastal waveguides. The wind forcing associated with this basin scale circulation closely matches surface wind signals associated with the Madden-Julian Oscillation. For more information read: Vialard, J., S. S. C. Shenoi, J. P. McCreary, D. Shankar, F. Durand, V. Fernando, and S. R. Shetye (2009), Intraseasonal response of the northern Indian Ocean coastal waveguide to the Madden-Julian Oscillation, Geophys. Res. Lett., 36, L14606, doi:10.1029/2009GL038450.

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