Flow Velocity Tidal Asymmetry in the Gulf of Khambhat, Arabian Sea using HF Radar Surface Currents
Samiran Mandal*, Sourav Sil, Avijit Gangopadhyay, Basanta Kumar Jena, R. Venkatesan, R. Balaji
Lane No. 7, Gandhinagar, Panchbaga, P.O.- Kenduadihi Dist-Bankura, West Bengal, India Pincode: 722102 Mobile: 9090353630 E-mail: email@example.com
The hourly ocean surface current observations from available High Frequency Radars (HFR) have been analyzed to identify the nature of tidal asymmetry in the inverted funnel-shaped Gulf of Khambhat (GoKh) on the western shelf of India. Tidal harmonic analysis of the HFR currents showed that the tidal currents at the mouth are dominated by the M2 constituent with amplitude ~4.5 times higher than that of K1. Among the shallow water constituents, M4 dominates the entire Gulf with significant amplitudes (~10 cm s-1) and gets amplified towards the head of the Gulf (~30 cm s-1), followed by MS4. Comparisons with sea level heights from tide gauges show a higher correlation for the major (>0.97) and shallow water (>0.96) tidal constituents in terms of the order of amplitudes of the tidal constituents. The circulation pattern in the Gulf is predominantly driven by tidal currents, with the total tidal variance being ~90% of the total current variance. The major contributions are from the M2 tidal currents (70-90%), except at the head, where the M4 component contributes significantly up to 40%. The harmonic analysis-derived relative surface phase (2M2 M4) and higher M4/M2 amplitude ratio at the head of the Gulf reveal that the Gulf is highly tidally asymmetric and flood dominant, indicating stronger non-linear tidal distortions in the nearshore regions. A generalized skewness-based analysis confirms the flood-dominance with positive values of a morphology-dependent asymmetry factor and skewness. Two tidal combinations (M2/M4 overtide and M2/S2/MS4 compound tide) are identified as the major contributors to the flow velocity skewness in the GoKh with mixed, mainly semi-diurnal tidal regime.