Nature of the observed oscillatory flows in shelf waters of the Western continental shelf of India

Abstract

Time series data on currents obtained from three Aanderaa current meters moored at a station depth of 92 m in the waters of the western continental shelf of India during May 1984 indicated the presence of oscillatory flows. The spectral computations revealed maximum in the semidiurnal frequency band with its magnitude higher by one order compared to that of the other bands. An analysis of phase differences together with coherence of flows at different levels and their amplitudes showed dominance of internal waves with frequencies close to semidiurnal period (internal tide) controlling the flow structure. The temperature records at these levels together with the B.T. time series data collected in the vicinity of mooring site supported the presence of internal waves. Semidiurnal characteristics computed from hydrographic data collected during the period of mooring across the shelf combined with the distribution of phases and amplitudes of horizontal velocities are found to be consistent with the generation of internal tides along the slope region. The barotropic and baroclinic nature of these currents separated and decomposed by averaging the data from all sensors and using empirical orthogonal functions respectively revealed the dominance of the former in the longshore component and the latter in the cross-shore component.