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 drogu ed at 15 m depth and had wind-produced slips less than 0.1 % of the wind sp eed. The rotary spectra of surface velocity components indicated the signif icance of inertial currents. They are circular (rotary coefficient > 0.5), highly intermittent and contribute up to 46 % to the total kinetic energy o f 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 c ycles. The observed inertial frequency exhibited a shift towards the red en d 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 scientifi ques et medicales Elsevier SAS.