A sea-level monopole in the equatorial Indian Ocean

Venugopal Thandlam*, T.V.S. Udaya Bhaskar, R. Hasibur, Paolo De Luca, E. Sahlée, A. Rutgersson, M. Ravichandran, S.S.V.S. Ramakrishna

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review


In this study, we show the relationship between sea-level anomalies (SLA) and upper-ocean parameters in the Equatorial Indian Ocean (EIO). This work also focuses on the variability of SLA obtained from satellite altimeter data in different spatial and temporal scales and its relationship with computed ocean heat content (OHC), dynamic height (DH), and thermocline depth (20 °C isotherm: D20) during 1993–2015. SLA showed low Pearson’s correlation coefficient (CC) with upper-ocean parameters over central EIO resembling a “Monopole” pattern. The Array for Real-time Geostrophic Oceanography (ARGO) in situ profile data in the central EIO also confirmed this. SLA over this monopole showed low correlations with all parameters as compared with eastern and western EIO. These findings show a clear signature of a persisting sea-level monopole in the central EIO. Oscillating SLA over western and eastern EIO during summer and winter monsoon months is found to be responsible for locking this monopole in the central EIO. Both SLA and OHC increased in EIO during 2006–2015 compared with 1993–2005. The month of January showed different east–west trends at different times. This trend during 1993–2015 is neutral, but it shifted from negative during 1993–2005 to positive during 2006–2015.

Original languageEnglish
Article number25
Issue number1
Publication statusPublished - 6 Jul 2020


The authors wish to thank Met Office, UK for providing EN4 observation data, and Indian National Center for Ocean Information Services (INCOIS), India for providing ARGO observations. The authors acknowledge the Argo data used in this paper, and these data were collected and made freely available by the International Argo Program and the national programs that contribute to it (http://www.argo.ucsd.edu, http://argo.jcommops.org). The Argo Program is part of the Global Ocean Observing System. The authors also thank Copernicus Marine Environment Monitoring Service (CMEMS) for providing SLA data. The authors also acknowledge the Department of Earth Sciences, Uppsala University, Uppsala Sweden, and INCOIS, India for the support and help to carry out this work. The authors acknowledge the research grant from Swedish Research Council (VR). Thanks to PyFerret software from NOAA, which was used to carry out data analysis, visualization, and to produce figures. We thank anonymous reviewers whose comments and suggestions have helped us to improve the paper. Open access funding provided by Uppsala University. This is INCOIS contribution number 381.

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Svenska Forskningsrådet Formas


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