Dynamics of Deep Sea Currents over Equatorial Indian Ocean (EIO) from Acoustic Doppler Current Meter (ADCP) and Recorded Current Meter (RCM) Observations

The periodic variability of deep sea currents in the Equatorial Indian ocean (EIO) studied by analyzing the moored current meter data collected during 2000-2006. The moored current meter data recorded Zonal and meridional currents at mean depths of 500m, 2000m and 4000m at three locations WEIO (0, 77°E), CEIO (0, 83°E) and EEIO (0, 93°E) along Equator in the Equatorial Indian Ocean (EEIO). The spectral energies at 10-20, 20-50, 50-90 and >90 days by using band passed analysis computed for the zonal and meridional currents. The spectrum gives a quantitative estimation of the variability of currents with periodic oscillations at different frequency bands. The spectrum shows the dominance of semi-annual periodic oscillations in zonal currents. The energy near semi-annual oscillations (170 days) is very high even in deeper layers at 4000m. The energy at low frequency oscillations decreased from WEIO to EEIO from surface to deeper depths up to 4000m. The Good coherence (>.85) was noticed at semi-annual period at three locations with upward phase propagation. The spectral peaks noticed at intra-seasonal oscillations (ISOs) and Madden-Julian oscillations (MJO) up to 4000m at all these mooring locations. The peaks and high spectral energies at semi-annual, Madden Julian and biweekly oscillations in the wind stress spectra clearly indicate the influence of wind stress on the currents in the deeper depths at 500m, 2000m and 4000m. This analysis also revealed that the dominance of meridional component in the high frequency oscillations. The increase in the spectral energies in the meridional components of currents at the high frequency oscillations (10-20 days) and intra-seasonal oscillations from WEEIO to the EEIO is a significant feature. The features indicate that these variations may influence the high frequency variability of north south variations of periodic oscillations to certain extent and even extended to deeper layers. Also these may enhance the sub intra and intra-seasonal   Oceanic processes from WEIO to EEIO in the Equatorial Indian   Ocean (EEIO).