Observed variability of the East India Coastal Current on the continental slope during 2009-2018
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Date
2020Author
Mukhopadhyay, S.
Shankar, D.
Aparna, S.G.
Mukherjee, A.
Fernando, V.
Kankonkar, A.
Khalap, S.
Satelkar, N.P.
Gaonkar, M.G.
Tari, A.P.
Khedekar, R.R.
Ghatkar, S.
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We describe the variability of the East India Coastal Current (EICC) during 2009-2018 using data from ADCP (acoustic Doppler current profiler) moorings deployed on the continental slope in the western Bay of Bengal. The four moorings are deployed off Gopalpur (~ 19. 5 ◦N), Visakhapatnam (~ 18 ◦N), Kakinada (~ 16 ◦N), and Cuddalore (~ 12 ◦N) on the Indian east coast. The longer data record allows us to attach a statistically more robust basis to the conclusions drawn by Mukherjee et al. (2014) on the basis of four years (2009-2013) of ADCP data. The data confirm that the seasonal cycle dominates the variability of the EICC. The amplitude of the annual band varies over the time series. In the intra-annual band, the variability switches between the semi-annual and 120-day bands off Gopalpur, Visakhapatnam and Kakinada, but the semi-annual band is stronger than the 120-day band off Cuddalore throughout the time series. Upward phase propagation is common in the seasonal bands, but downward phase propagation is common in the intra-annual band off Cuddalore during the summer and winter monsoons, leading to stronger undercurrents there. Off Cuddalore, even the annual EICC appears as a shallow current. In contrast, the EICC appears as a deep flow off Gopalpur, Visakhapatnam, and Kakinada particularly during the spring inter-monsoon. This deep flow is evident at these locations even in the intraseasonal (30-90-day) band; the longer data set suggests, however, that the intraseasonal variability does not necessarily peak during spring. The annual EICC is coherent along the coast, but it is only the semi-annual band that shows a comparable coherence between Kakinada and Cuddalore: in the 120-day and intraseasonal bands, the EICC decorrelates along the coast. Wavelet analysis suggests significant variability at sub-annual periods. The sub-annual EICC exceeds 20cms-1 on many occasions, but it too decorrelates along the coast. The long ADCP record allows us to confirm the dominance of seasonality in the EICC regime in a robust fashion; the data show that the EICC tends to flow in its canonical poleward (equatorward) direction during spring (winter). This dominance of seasonality enhances the predictability of the EICC.
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