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ABSTRACT
The Arabian Sea (AS), a basin in the North Indian Ocean (NIO), possesses strong coastal upwelling in its eastern and western margins. The spatio-temporal variability of upwelling over Somalia, Oman and the southwest coast of India is analysed using observed datasets. The spectral analysis of upwelling indices highlights that the semi-annual and annual frequencies were dominant by two orders of magnitude compared with the inter-annual variability over these upwelling zones. The inter-annual variability of coastal upwelling was demarcated with variations in the causative forcing of upwelling associated with the positive modes of Indian Ocean Dipole (pIOD), El-Niño Southern Oscillation (El-Niño) and combined pIOD and El-Niño events over the southwest coast of India (SWCI) and Somalia. Along SWCI, the sea surface temperature and meridional wind stress weakened leading to warming associated with the suppression of upwelling during El-Niño, pIOD and combined events. Along Somalia, the upwelling favourable wind stress showed slight weakening due to pIOD and strong decline due to El-Niño and combined modes. Along Oman, the upwelling favourable wind stress indicated negligible changes due to pIOD, an increase due to El-Niño and a slight decline due to combined modes.
Acknowledgements
The authors thank the high-performance computing (HPC) facility provided by IIT Delhi and the Department of Science and Technology (DST-FIST 2014 at CAS), Government of India. Funding support from the Ministry of Earth Sciences (MoES, Govt. of India) is thankfully acknowledged. Graphics were generated in this paper using Python, Ferret and NCL. Tanuja Nigam acknowledges IRIS, IRD and IIT Delhi, MoES, respectively, for her early Doc fellowship and PhD fellowship support.
Author contributions
TN and VP have planned the framework of the draft. TN performed analysis and prepared plots. TN has written the draft manuscript and VP has improved the manuscript with numerous corrections and contributions from the co-author.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Additional information
Notes on contributors
Tanuja Nigam
Tanuja Nigam has a doctoral degree in Physical Oceanography from Indian Institute of Technology Delhi, India and currently working as a Scientist in Physical Oceanography Division of CSIR-National Institute of Oceanography, Goa, India.
Vimlesh Pant
Vimlesh Pant is a Professor at Centre for Atmospheric Sciences, Indian Institute of Technology Delhi, New Delhi, India. His research areas are physical oceanography, ocean modelling, and air-sea interaction.