Abstract
We describe the variability of the West India Coastal Current (WICC) during 2009–2017 using data from acoustic Doppler current profilers (ADCPs) attached to moorings deployed on the outer shelf at a water-column depth of 100–200 m at three locations: off Kollam (9°N), Bhatkal (13.9°N), and Goa (15°N). Our study shows that the characteristics of the WICC on the outer shelf are similar to those observed on the slope except for the occasional decorrelation observed between them. Both shelf and slope WICC have a weak mean flow and a strong annual cycle. As seen on the slope, the depth of the undercurrent on the shelf changes with season because of the strong upward phase propagation associated with the annual cycle. Though the currents at all three shelf locations exhibit a strong seasonal cycle, there are prominent differences between the currents off the southwest coast of India (Kollam) and the central west coast of India (Bhatkal and Goa). The seasonal cycle off Kollam is often punctuated by strong intraseasonal bursts, which cause the shelf WICC off Kollam to be highly unpredictable; this unpredictability implies that on a given day of the year, one cannot expect a poleward (equatorward) current during the winter (summer) monsoon. On the central west coast, the poleward (equatorward) direction during the winter monsoon (summer monsoon) is prominent. Comparison with the available datasets shows that the WICC is occasionally coherent along and across the shelf, and the coherence is stronger for the seasonal cycle.
Research highlights
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1.
Characteristics of the WICC on the outer shelf are similar to those observed on the slope.
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Shelf WICC has a weak mean flow and a strong annual cycle.
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3.
Differences observed between currents off central west coast and southwest coast of India.
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4.
Seasonal cycle off Kollam is often punctuated by strong intraseasonal bursts.
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Acknowledgements
The ADCP mooring project has been supported by grants from the Council of Scientific and Industrial Research (CSIR) (under the Supra-Institutional Program of CSIR-NIO during 2007–2012, under OCEAN FINDER during 2012–2017, and TRIMFish thereafter) and the Ministry of Earth Sciences (MoES, via INCOIS) through its programme on Ocean Observing Networks. These shelf moorings were inspired by Dr S R Shetye and he and Dr Shenoi were involved in the initial planning phase of the mooring network. The support from ESSO-INCOIS, the CSIR-NIO ship cell, and the officers and crew on board the research vessels are acknowledged with gratitude. The tide-gauge data were obtained from ESSO-INCOIS. A part of this work is from the doctoral research carried out at CSIR-NIO by P Amol. A Chaudhuri was supported by the Science and Engineering Research Board (SERB) vide project PDF/2017/000302 from September 2017 to August 2019 and she acknowledges the support from CSIR-NIO for the use of facilities during the duration of this work. P. Amol thanks the Science and Engineering Research Board (SERB) (Grant No. SR/FTP/ES-3/2015) for funding. We thank Rahul. R. Khedekar for help with processing ADCP data. Ferret and R have been used for analysis and for graphics; the R package for wavelet analysis was downloaded from http://tocsy.agnld.uni-potsdam.de/wavelets. The Lomb Periodogram was calculated using the LOMB package (Ruf 1999) in R. The CEOF analysis was done in OCTAVE with PCAtool (https://www.mathworks.com/matlabcentral/fileexchange/17915-pcatool). This is CSIR-NIO contribution 6682.
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DS and VF conceived, designed, and coordinated the mooring programme (with initial contribution from Satheesh Shenoi and Satish Shetye). VF, AK, and PA were involved in data acquisition. AC, SM, AK, and SGA processed, analysed, and interpreted the data. AC and PA drafted the manuscript. DS and SGA provided critical feedback and helped shape the manuscript.
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Supplementary material pertaining to this article is available on the Journal of Earth System Science website (http://www.ias.ac.in/Journals/Journal_of_Earth_System_Science).
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Chaudhuri, A., Amol, P., Shankar, D. et al. Observed variability of the West India Coastal Current on the continental shelf from 2010–2017. J Earth Syst Sci 130, 77 (2021). https://doi.org/10.1007/s12040-021-01603-4
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DOI: https://doi.org/10.1007/s12040-021-01603-4