• S T KHALAP

      Articles written in Journal of Earth System Science

    • Observed variability of the West India Coastal Current on the continental slope from 2009–2018

      ANYA CHAUDHURI D SHANKAR S G APARNA P AMOL V FERNANDO A KANKONKAR G S MICHAEL N P SATELKAR S T KHALAP A P TARI M G GAONKAR S GHATKAR R R KHEDEKAR

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      We describe the variability of the West India Coastal Current (WICC) during October 2008 to October 2018 using data from ADCP (acoustic Doppler current profiler) moorings deployed on the continental slope off the west coast of India. The four moorings are deployed off Mumbai ($\sim 20^{0}\rm{N}$), Goa ($\sim 15^{0}\rm{N}$), Kollam ($\sim 9^{0}\rm{N}$), and Kanyakumari ($\sim 7^{0}\rm{N}$). This 10-year data set allows us to attach a statistical significance to the conclusions drawn by Amol et al. (2014) on the basis of four years (October 2008–October 2012) of ADCP data. The longer data set confirms the earlier finding that intraseasonal variability in the 30–90-day band dominates the variability of the WICC at all locations and that this intraseasonal variability peaks during the winter monsoon. The annual cycle (300–400 days) is strong and statistically significant at all locations. The phase propagates upward for the annual cycle and this phase difference is seen in the relative phases of both, the ADCP currents at 25 and 48 m as well as the 48 m ADCP and satellite-derived currents. The intra-annual (100–250 days) and intraseasonal currents show instances of both upward and downward phase propagation. The alongshore wavelet coherence is high on seasonal time scales between adjacent mooring locations and several instances of high coherence are seen even on intraseasonal time scales. Data gaps off Goa and Kanyakumari restrict the significant wavelet power to the ADCP records off Kollam and Mumbai, and the coherence analysis shows that the WICC off Kollam leads Mumbai on seasonal scales. The direction of the alongshore WICC is, however, largely determined by the direction of the significantly larger intraseasonal component. Though the climatological seasonal cycle over the whole record does show the canonical equator ward flow during the summer monsoon (June–September) and poleward flow during the winter monsoon (November–February), the scatter around the daily mean is very high.The data show that the WICC may flow in either direction on a given day of the year, with this unpredictability of direction being stronger off Kollam, where the $1-\sigma$ band of the daily mean alongshore WICC shows that it can flow in either direction in most months. The seasonality is stronger off Mumbai, where the width of the $1-\sigma$ band is less. The decade-long continuous record off Kollam and Mumbai shows that the sub-annual along shore WICC at both locations is significant and is comparable to or stronger than the annual component.The cross-shore sub-annual current is also strong off Kollam and is seen to be associated with eddy-like circulations.

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