Seasonal and Tidal Variability of Surface Currents in the Western Andaman Sea Using HF Radars and Buoy Observations During 2016–2017

The characteristics of surface currents during November 2016-October 2017 are studied using observations from the high-frequency radars (HFRs) and a moored buoy (BD12) along the western Andaman Sea (WAnS). The comparison of HFR currents with the collocated currents from BD12 shows a high correlation (>0.78) on a daily scale for both the components. Moreover, the daily HFR currents compared reasonably well to the composite daily surface currents from multiple satellites for both the zonal and meridional components. The reversal of currents is observed during the northeast (November-February) and southwest (June-October) monsoons with the mean current magnitudes of 0.41 m/s northward and 0.22 m/s southward, respectively, which is predominantly influenced by the local wind stress. The seasonal reversal of currents leads to the exchange of waters between the WAnS and the Bay of Bengal through the 11° channel, which is primarily due to the Ekman mass transport. Harmonic analysis of the hourly data from HFRs shows the dominance of M2 tidal currents, followed by other semidiurnal (S2, N2), diurnal (K1, O1), and shallow water constituents (M4 and MS4). Also, the tidal constituents from both the current observations matched in their relative order of amplitudes with a reasonable correlation (0.95). Total tidal variance ranges between 10% and 50% in the WAnS, with the highest contributions from the M2 tidal currents (of 25%). Moreover, stronger M2 tidal currents are observed to skirt around Little Andaman (LA) Island extending out to 100-km offshore, with maximum amplitudes of 12 cm/s.