Abstract
Deep-sea moorings in the equatorial Indian Ocean were first deployed by India in the year 2000, and currents were measured at three locations (\(77^\circ \hbox {E}\), \(83^\circ \hbox {E}\), and \(93^\circ \hbox {E}\)) on the equator. In this paper, we present two decades of current observations from these moorings and discuss how the moorings have evolved with time. The observations show that the 180-day (90-day) period dominates the surface and mid-depth (bottom) circulation. Though the Wyrtki Jets are strong, the near-surface currents do not show any clear semi-annual reversals. The reversals become evident only below 100 m.
Research Highlights
-
1.
Twenty years of ocean current data collected at the equatorial Indian Ocean
-
2.
Bottom current data show strong intraseasonal variability
-
3.
Upward phase propagation associated with the semi-annual cycle more prominent for the mid-depth currents
-
4.
The semi-annual reversals not evident every year near the surface
This is a preview of subscription content, log in via an institution to check access.
References
Beal L, Vialard J, Koll R, Ravichandran M, McPhaden M, Feng M, Lumpkin R, Alakkat U, Lee T, Sloyan B, Andres M, Subramanian A, Yu L, Lengaigne M, Shinoda T, Annamalai H, Ummenhofer C, Strutton P, Masumoto Y and Hood R 2019 IndOOS-2: A roadmap to sustained observations of the Indian Ocean for 2020-2030; CLIVAR-4/2019, GOOS-237, https://doi.org/10.36071/clivar.rp.4.2019.
David D T, Kumar S P, Byju P, Sarma M S S, Suryanarayana A and Murty V S N 2011 Observational evidence of lower-frequency Yanai waves in the central equatorial Indian Ocean; J. Geophys. Res. 116(C6), https://doi.org/10.1029/2010JC006603.
Gnanaseelan C, Deshpande A and McPhaden M J 2012 Impact of Indian Ocean Dipole and El Niño/Southern Oscillation wind-forcing on the Wyrtki jets; J. Geophys. Res. 117(C8), https://doi.org/10.1029/2012JC007918.
Han W 2005 Origins and dynamics of the 90-day and 30–60-day variations in the Equatorial Indian Ocean; J. Phys. Oceanogr. 35(5) 708–728, https://doi.org/10.1175/JPO2725.1.
Huang K, McPhaden M J, Wang D, Wang W, Xie Q, Chen J, Shu Y, Wang Q, Li J and Yao J 2018 Vertical propagation of middepth zonal currents associated with surface wind forcing in the Equatorial Indian Ocean; J. Geophys. Res. 123(10) 7290–7307, https://doi.org/10.1029/2018JC013977.
McCreary J P, Kundu P K and Molinari R L 1993 A numerical investigation of dynamics, thermodynamics and mixed-layer processes in the Indian Ocean; Prog. Oceanogr. 31(3)181–244, https://doi.org/10.1016/0079-6611(93)90002-U.
McPhaden M J, Meyers G, Ando K, Masumoto Y, Murty V S N, Ravichandran M, Syamsudin F, Vialard J, Yu L and Yu W 2009 RAMA: The Research Moored Array for African–Asian–Australian Monsoon Analysis and Prediction; Bull. Am. Meteorol. Soc. 90(4) 459–480, https://doi.org/10.1175/2008BAMS2608.1.
McPhaden M J, Wang Y and Ravichandran M 2015 Volume transports of the Wyrtki jets and their relationship to the Indian Ocean Dipole; J. Geophys. Res. 20(8) 5302–5317, https://doi.org/10.1002/2015JC010901.
Murty V S N, Suryanarayana A, Sarma M S S, Tilvi V, Fernando V, Nampoothiri G, Sardar A, Gracias D and Khalap S 2002 First results of Indian Current meter moorings along the equator: Vertical current structure variability at equator, 93°E during February–December, 2000; In: Proceedings of The Sixth Pan Ocean Remote Sensing Conference (PORSEC), Bogor, Indonesia.
Murty V S N, Sarma M S S, Suryanarayana A, Sengupta D, Unnikrishnan A S, Fernando V, Almeida A M, Khalap S, Sardar A, Somasundar K and Ravichandran M 2006 Indian moorings: Deep-sea current meter moorings in the Eastern Equatorial Indian Ocean; CLIVAR Exchanges 11(4).
Ogata T, Sasaki H, Murty V S N, Sarma M S S and Masumoto Y 2008 Intraseasonal meridional current variability in the eastern equatorial Indian Ocean; J. Geophys. Res. 113(C7), https://doi.org/10.1029/2007JC004331.
Schott F A and McCreary J P 2001 The monsoon circulation of the Indian Ocean; Prog. Oceanogr. 51(1) 1–123, https://doi.org/10.1016/S0079-6611(01)00083-0.
Sengupta D, Senan R, Murty V S N and Fernando V 2004 A biweekly mode in the equatorial Indian Ocean; J. Geophys. Res. 109(C10), https://doi.org/10.1029/2004JC002329.
Shankar D, Vinayachandran P N and Unnikrishnan A S 2002 The monsoon currents in the north Indian Ocean; Prog. Oceanogr. 52 63–120, https://doi.org/10.1016/S0079-6611(02)00024-1.
Vinayachandran P N and Shetye S R 1991 The warm pool in the Indian Ocean; Proc. Indian Acad. Sci. - Earth Planet. Sci. 100(2) 165–175, https://doi.org/10.1007/BF02839431.
Acknowledgements
The authors thank M S S Sarma, A Suryanarayana, D Gracias, late R J K Charyulu, P Ganapathi, S Paul, K Venkateswara Rao, and K Chandrasekar for their involvement in the equatorial mooring program. The support from the CSIR-NIO ship cell members (M S Kerkar, S P Vernekar and A C D’Souza), officers, crew, and seamen from various cruises is gratefully acknowledged. The comments from D Shankar helped improve this paper considerably. The mooring operations were carried out on the research vessels O R V Sagar Kanya, O R V Sindhu Sadhana, and O R V Sagar Nidhi. Financial support for this project was provided by MoES via their Ocean Observation Network (OON) programme and CSIR. VJ acknowledges funding support from ESSO-INCOIS. Ferret (PMEL/NOAA) and GMT were used for analysis and graphics. This is CSIR-NIO contribution 6661.
Author information
Authors and Affiliations
Contributions
V S N Murty, V Fernando, A M Almeida, Areef A Sardar, S T Khalap, N P Satelkar, S Ghatkar, A Kankonkar, P A Tari, M G Gaonkar, and P Amol were involved in data acquisition. Vineet Jain, P Amol, and S G Aparna drafted the manuscript. Vineet Jain and A Kankonkar processed, analysed and interpreted the data. Vineet Jain, P Amol, S G Aparna, V S N Murty, and V Fernando conceived and designed the study.
Corresponding author
Additional information
Communicated by C Gnanaseelan
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).
Supplementary Information
Rights and permissions
About this article
Cite this article
Jain, V., Amol, P., Aparna, S.G. et al. Two decades of current observations in the equatorial Indian Ocean. J Earth Syst Sci 130, 75 (2021). https://doi.org/10.1007/s12040-021-01568-4
Received:
Revised:
Accepted:
Published:
DOI: https://doi.org/10.1007/s12040-021-01568-4