Intraseasonal response of the northern Indian Ocean coastal waveguide to the Madden-Julian Oscillation
|Author(s)||Vialard Jerome1, Shenoi S. S. C.2, McCreary J. P.5, Shankar D.4, Durand F.3, Fernando V.4, Shetye S. R.4|
|Affiliation(s)||1 : Univ Paris 06, IRD, LOCEAN, F-75232 Paris 05, France.
2 : Indian Natl Ctr Ocean Informat Serv, Hyderabad 500055, Andhra Pradesh, India.
3 : IRD, Lab Etud Geophys & Oceanog Spatiales, F-31400 Toulouse, France.
4 : CSIR, Natl Inst Oceanog, Phys Oceanog Div, Panaji 403004, Goa, India.
5 : Univ Hawaii, Int Pacific Res Ctr, Honolulu, HI 96822 USA.
|Source||Geophysical Research Letters (0094-8276) (Amer Geophysical Union), 2009-07 , Vol. 36 , N. LI4606 , P. 1-5|
|WOS© Times Cited||58|
|Keyword(s)||variability, dynamics, circulation, currents|
|Abstract||A new observational record of upper-ocean currents at 15 degrees 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 degrees N, the minimum period for planetary waves is similar to 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.|