Seasonal variability in the vertical current structure and kinetic energy in the Central Indian Ocean Basin

Seasonal variability in the currents at the subsurface (450-670 m), interme diate (1150-1370 m), deeper (3450-3670m) and near-bottom (4270-5100m) depth s at three mooring stations in the Central Indian Ocean Basin (CIOB) were d ocumented in 1995-1997. The current-meter moorings were deployed thrice at station 1 (MS-1, MS-1A and MS-1B) in the northern basin (similar to 10 degr eesS), and twice at stations 2 (MS-2 and MS-2A) and 3 (MS-3 and MS-3A) in t he southern basin (similar to 15 degreesS). In the northern basin, seasonal variability in the currents at 500m and 1200m depth is due to the seasonal north-south shift in the westward-flowing South Equatorial Current (SEC). Low-frequency (30-60 day) oscillation, superimposed on high-frequency (iner tial, semi-diurnal and diurnal) fluctuations, is noticed at all the depths including near-bottom depth (5100m) where the U-component of current was do minant. The variability of the currents at the intermediate depth range (11 50-1300 m), encompassing the three stations of 500 km apart, indicates the existence of anticyclonic gyral circulation. The depth variation of kinetic energy (KE) emphasises the bottom intensification of currents with minimum KE at deeper depths followed by relatively higher KE at abyssal depths. In the northern basin, the total KE exhibits seasonal variation; it is high d uring southern spring-summer and low during southern fall-winter. The eddy KE constitutes a larger part of the total KE at synoptic scale (12-15 day) fluctuations in the northern basin and meso-scale (inertial, semi-diurnal a nd diurnal) oscillations in the southern basin. (C) 2001 Elsevier Science L td. All rights reserved.