Inertial currents in the Indian Ocean derived from satellite tracked surface drifters

Satellite-tracked surface drifters were used to analyze the characteristics of inertial currents in the tropical Indian Ocean. The drifters were drogued at 15 m depth and had wind-produced slips less than 0.1 % of the wind speed. The rotary spectra of surface velocity components indicated the significance of inertial currents. They are circular (rotary coefficient > 0.5), highly intermittent and contribute up to 46 % to the total kinetic energy of the surface flow field. Events of inertial activity, either triggered by the passage of atmospheric disturbances or by the local fluctuations in the atmospheric pressure (winds), did not last for more than 4 to 5 inertial cycles. The observed inertial frequency exhibited a shift towards the red end of the spectrum by 12 %. Cyclonic storm induced inertial events even at a location 300 km away from it. (C) 2000 Ifremer/CNRS/IRD/Editions scientifiques et medicales Elsevier SAS.