Validation and Tidal Analysis of HF Radar Derived Ocean Surface Currents along the Odisha Coast, nothwestern Bay of Bengal

This work presents results from analysis of the High Frequency Radar (HFR) derived ocean surface current observations along the Odisha coast of India during 2010. The work is mainly divided into three parts, the i) validation of HFR currents, ii) high frequency variability and iii) investigating the impact of stratification and winds on tidal currents. Due to lack of in situ current measurements in this region, the HFR currents are validated with algorithm derived surface currents from satellite observations consisting of three components namely, the wind-driven (Ekman) component, geostrophic component and buoyancy component on daily scale. These two datasets are matching reasonably well with correlation coefficients of 0.90 and 0.69 for the zonal and meridional components, respectively. The harmonic analysis of the zonal and meridional components of HFR datasets indicate that among semi-diurnal tidal components M2 dominates over S2 and N2 in the North-Western Bay of Bengal, however, K1 also dominates at times. Furthermore, the other well-known diurnal tidal components O1 and Q1 have also been observed, pointing out that the tidal regime is of mixed type and mainly semi-diurnal. The semi-major axis amplitudes associated with M2 and K1 tidal ellipses are 7.16 (6.13) cm s^-1 and 4.02 (3.30) cm s^-1 respectively in the nearshore (offshore) location to indicate that tidal currents relatively stronger in the nearshore location. From the analysis, it is quite clear that bathymetry plays a significant role in tidal amplification. Moreover, the impact of stratification (highly stratified during August-November) and seasonally reversing nature of the monsoonal winds on the HFR currents has also been investigated. The dominating K1 tidal constituent can definitely be attributed to the diurnal variability of winds. The significant shallow water constituents S4, MS4 and M3 (M4, 2SM6 and M6) with amplitudes of semi-major axis of about 1 to 2 cm s^-1 are identified at nearshore (offshore) location, which appear due to interaction of tidal current with bathymetry.