Multiscale Sea Level Variability, Surface Geostrophic Circulation and Mesoscale Eddy Dynamics in the Tropical Western Indian Ocean: Insights from Satellite Altimetry (1993-2024)
The Western Indian Ocean (WIO) is one of the most dynamically active ocean regions globally, yet its multiscale interactions and collective influence on sea level variability, surface circulation, and mesoscale eddy activity remain unquantified across the full satellite altimetry era despite direct effect on regional climate prediction, coastal adaptation, and marine ecosystem management along the East African coastline. This study presents an integrated analysis across the tropical WIO (40˚E - 52˚E, 20˚S - 12˚N) using a 32-year satellite altimetry record (1993-2024), employing seasonal decomposition, linear regression with autocorrelation-adjusted significance testing, a non-parametric trend test, and Pearson and partial correlation analysis. Seasonal SLA patterns reveal a monsoon-driven annual cycle characterized by the strongest positive anomalies during MAM, a pronounced cross-equatorial dipole during JJA, and a localized negative coastal anomaly during SON unique to that season. Domain-averaged seasonal SLA exhibits significant positive trends of 3.54 - 4.17 mm yr−1, with an annual mean trend of 3.81 mm yr−1 exceeding the global rate of 3.3 - 3.4 mm yr−1. Both El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) significantly modulate WIO sea level during DJF, while ENSO remains significant when controlling for IOD during MAM as IOD remains significant when controlling ENSO during SON while neither index is significant during JJA. Surface geostrophic circulation confirms the monsoon-driven Somali Current reversal and the year-round persistence SEC-EACC western boundary current system. While decrease in mesoscale eddy activity has been reported for many tropical ocean regions, the tropical WIO exhibits significant EKE intensification across all seasons, highlighting the distinctive dynamics of this boundary-current-dominated region. SON is more energetic than MAM across circulation and EKE, while MAM exhibits the strongest positive SLA signal of the annual cycle. These findings advance understanding of WIO multiscale ocean dynamics, providing an observational baseline for regional climate prediction and early warning systems in the region.Subject AreasPhysical Oceanography, Climate Science, Remote Sensing
Cite this paper
Kutsuru, K. , Makokha, J. W. and Khamala, G. W. (2026). Multiscale Sea Level Variability, Surface Geostrophic Circulation and Mesoscale Eddy Dynamics in the Tropical Western Indian Ocean: Insights from Satellite Altimetry (1993-2024). Open Access Library Journal, 13, e15773. doi: http://dx.doi.org/10.4236/oalib.1115773.
Roxy, M.K., Ritika, K., Terray, P. and Masson, S. (2014) The Curious Case of Indian Ocean Warming. <i>Journal</i> <i>of</i> <i>Climate</i>, 27, 8501-8509. <br>https://doi.org/10.1175/jcli-d-14-00471.1
Black, E., Slingo, J. and Sperber, K.R. (2003) An Observational Study of the Relationship between Excessively Strong Short Rains in Coastal East Africa and Indian Ocean SST. <i>Monthly</i> <i>Weather</i> <i>Review</i>, 131, 74-94. <br>https://doi.org/10.1175/1520-0493(2003)131<0074:aosotr>2.0.co;2
Lévy, M., Shankar, D., André, J.M., Shenoi, S.S.C., Durand, F. and de Boyer Montégut, C. (2007) Basin-Wide Seasonal Evolution of the Indian Ocean’s Phytoplankton Blooms. <i>Journal</i> <i>of</i> <i>Geophysical</i> <i>Research</i>: <i>Oceans</i>, 112, C12014. <br>https://doi.org/10.1029/2007jc004090
Roxy, M.K., Modi, A., Murtugudde, R., Valsala, V., Panickal, S., Prasanna Kumar, S., <i>et al</i>. (2016) A Reduction in Marine Primary Productivity Driven by Rapid Warming over the Tropical Indian Ocean. <i>Geophysical Research Letters</i>, 43, 826-833. <br>https://doi.org/10.1002/2015gl066979
Dalpadado, P., Roxy, M.K., Arrigo, K.R., van Dijken, G.L., Chierici, M., Ostrowski, M., <i>et al</i>. (2024) Rapid Climate Change Alters the Environment and Biological Production of the Indian Ocean. <i>Science of the Total Environment</i>, 906, Article ID: 167342. <br>https://doi.org/10.1016/j.scitotenv.2023.167342
Ballesteros, C. and Esteves, L.S. (2021) Integrated Assessment of Coastal Exposure and Social Vulnerability to Coastal Hazards in East Africa. <i>Estuaries</i> <i>and</i> <i>Coasts</i>, 44, 2056-2072. <br>https://doi.org/10.1007/s12237-021-00930-5
Joseph, L., Dey, D., Skliris, N., Sanchez‐Franks, A., Marsh, R., Hirschi, J., <i>et al</i>. (2025) Warming Trend in the Western Indian Ocean Driven by Oceanic Transport. <i>Journal</i> <i>of</i> <i>Geophysical</i> <i>Research</i>: <i>Oceans</i>, 131, e2025JC022762. <br>https://doi.org/10.1029/2025jc022762
Jacobs, Z.L., Yool, A., Jebri, F., Srokosz, M., van Gennip, S., Kelly, S.J., <i>et al</i>. (2021) Key Climate Change Stressors of Marine Ecosystems along the Path of the East African Coastal Current. <i>Ocean</i> <i>&</i> <i>Coastal</i> <i>Management</i>, 208, Article ID: 105627. <br>https://doi.org/10.1016/j.ocecoaman.2021.105627
Schott, F.A. and McCreary, J.P. (2001) The Monsoon Circulation of the Indian Ocean. <i>Progress</i> <i>in</i> <i>Oceanography</i>, 51, 1-123. <br>https://doi.org/10.1016/s0079-6611(01)00083-0
Wang, H., McClean, J.L., Talley, L.D. and Yeager, S. (2018) Seasonal Cycle and Annual Reversal of the Somali Current in an Eddy-Resolving Global Ocean Model. <i>Journal</i> <i>of</i> <i>Geophysical</i> <i>Research</i>: <i>Oceans</i>, 123, 6562-6580. <br>https://doi.org/10.1029/2018jc013975
Schott, F., Fischer, J., Garternicht, U. and Quadfasel, D. (1997) Summer Monsoon Response of the Northern Somali Current, 1995. <i>Geophysical</i> <i>Research</i> <i>Letters</i>, 24, 2565-2568. <br>https://doi.org/10.1029/97gl00888
Trott, C.B., Subrahmanyam, B. and Murty, V.S.N. (2017) Variability of the Somali Current and Eddies during the Southwest Monsoon Regimes. <i>Dynamics of Atmospheres and Oceans</i>, 79, 43-55. <br>https://doi.org/10.1016/j.dynatmoce.2017.07.002
Trott, C.B., Subrahmanyam, B., Chaigneau, A. and Delcroix, T. (2018) Eddy Tracking in the Northwestern Indian Ocean during Southwest Monsoon Regimes. <i>Geophysical</i> <i>Research</i> <i>Letters</i>, 45, 6594-6603. <br>https://doi.org/10.1029/2018gl078381
Ridderinkhof, H. and de Ruijter, W.P.M. (2003) Moored Current Observations in the Mozambique Channel. <i>Deep</i> <i>Sea</i> <i>Research</i> <i>Part</i> <i>II</i>: <i>Topical</i> <i>Studies</i> <i>in</i> <i>Oceanography</i>, 50, 1933-1955. <br>https://doi.org/10.1016/s0967-0645(03)00041-9
Halo, I., Backeberg, B., Penven, P., Ansorge, I., Reason, C. and Ullgren, J.E. (2014) Eddy Properties in the Mozambique Channel: A Comparison between Observations and Two Numerical Ocean Circulation Models. <i>Deep</i> <i>Sea</i> <i>Research</i> <i>Part</i> <i>II</i>: <i>Topical</i> <i>Studies</i> <i>in</i> <i>Oceanography</i>, 100, 38-53. <br>https://doi.org/10.1016/j.dsr2.2013.10.015
Shankar, D., Vinayachandran, P.N. and Unnikrishnan, A.S. (2002) The Monsoon Currents in the North Indian Ocean. <i>Progress</i> <i>in</i> <i>Oceanography</i>, 52, 63-120. <br>https://doi.org/10.1016/s0079-6611(02)00024-1
Masumoto, Y. and Meyers, G. (1998) Forced Rossby Waves in the Southern Tropical Indian Ocean. <i>Journal</i> <i>of</i> <i>Geophysical</i> <i>Research</i>: <i>Oceans</i>, 103, 27589-27602. <br>https://doi.org/10.1029/98jc02546
Clarke, A.J. and Liu, X. (1994) Interannual Sea Level in the Northern and Eastern Indian Ocean. <i>Journal</i> <i>of</i> <i>Physical</i> <i>Oceanography</i>, 24, 1224-1235. <br>https://doi.org/10.1175/1520-0485(1994)024<1224:islitn>2.0.co;2
Rao, S.A., Behera, S.K., Masumoto, Y. and Yamagata, T. (2002) Interannual Subsurface Variability in the Tropical Indian Ocean with a Special Emphasis on the Indian Ocean Dipole. <i>Deep</i> <i>Sea</i> <i>Research</i> <i>Part</i> <i>II</i>: <i>Topical</i> <i>Studies</i> <i>in</i> <i>Oceanography</i>, 49, 1549-1572. <br>https://doi.org/10.1016/s0967-0645(01)00158-8
Feng, M. and Meyers, G. (2003) Interannual Variability in the Tropical Indian Ocean: A Two-Year Time-Scale of Indian Ocean Dipole. <i>Deep</i> <i>Sea</i> <i>Research</i> <i>Part</i> <i>II</i>: <i>Topical</i> <i>Studies</i> <i>in</i> <i>Oceanography</i>, 50, 2263-2284. <br>https://doi.org/10.1016/s0967-0645(03)00056-0
Church, J.A. and White, N.J. (2011) Sea-Level Rise from the Late 19th to the Early 21st Century. <i>Surveys</i> <i>in</i> <i>Geophysics</i>, 32, 585-602. <br>https://doi.org/10.1007/s10712-011-9119-1
Han, W., Meehl, G.A., Rajagopalan, B., Fasullo, J.T., Hu, A., Lin, J., <i>et al</i>. (2010) Patterns of Indian Ocean Sea-Level Change in a Warming Climate. <i>Nature</i> <i>Geoscience</i>, 3, 546-550. <br>https://doi.org/10.1038/ngeo901
Yue, S. and Wang, C.Y. (2002) Applicability of Prewhitening to Eliminate the Influence of Serial Correlation on the Mann-Kendall Test. <i>Water</i> <i>Resources</i> <i>Research</i>, 38, 4-1-4-7. <br>https://doi.org/10.1029/2001wr000861
Yue, S. and Wang, C. (2004) The Mann-Kendall Test Modified by Effective Sample Size to Detect Trend in Serially Correlated Hydrological Series. <i>Water</i> <i>Resources</i> <i>Management</i>, 18, 201-218. <br>https://doi.org/10.1023/b:warm.0000043140.61082.60
Sen, P.K. (1968) Estimates of the Regression Coefficient Based on Kendall’s Tau. <i>Journal</i> <i>of</i> <i>the</i> <i>American</i> <i>Statistical</i> <i>Association</i>, 63, 1379-1389. <br>https://doi.org/10.1080/01621459.1968.10480934
Rieck, J.K., Böning, C.W., Greatbatch, R.J. and Scheinert, M. (2015) Seasonal Variability of Eddy Kinetic Energy in a Global High-Resolution Ocean Model. <i>Geophysical</i> <i>Research</i> <i>Letters</i>, 42, 9379-9386. <br>https://doi.org/10.1002/2015gl066152
Wyrtki, K. (1973) Physical Oceanography of the Indian Ocean. In: Zeitzschel, B. and Gerlach, S.A., Eds., <i>The</i><i> Biology of the Indian Ocean</i>, Springer, 18-36. <br>https://doi.org/10.1007/978-3-642-65468-8_3
Li, N., Zhu, X., Wang, H., Zhang, S. and Wang, X. (2023) Intraseasonal and Interannual Variability of Sea Temperature in the Arabian Sea Warm Pool. <i>Ocean</i> <i>Science</i>, 19, 1437-1451. <br>https://doi.org/10.5194/os-19-1437-2023
Findlater, J. (1969) A Major Low-Level Air Current near the Indian Ocean during the Northern Summer. <i>Quarterly</i> <i>Journal</i> <i>of</i> <i>the</i> <i>Royal</i> <i>Meteorological</i> <i>Society</i>, 95, 362-380. <br>https://doi.org/10.1002/qj.49709540409
Beal, L.M. and Donohue, K.A. (2013) The Great Whirl: Observations of Its Seasonal Development and Interannual Variability. <i>Journal</i> <i>of</i> <i>Geophysical</i> <i>Research</i>: <i>Oceans</i>, 118, 1-13. <br>https://doi.org/10.1029/2012jc008198
Schouten, M.W., de Ruijter, W.P.M., van Leeuwen, P.J. and Ridderinkhof, H. (2003) Eddies and Variability in the Mozambique Channel. <i>Deep</i> <i>Sea</i> <i>Research</i> <i>Part</i> <i>II</i>: <i>Topical</i> <i>Studies</i> <i>in</i> <i>Oceanography</i>, 50, 1987-2003. <br>https://doi.org/10.1016/s0967-0645(03)00042-0
Masson-Delmotte, V., Zhai, P., Pirani, A., Connors, S.L., Péan, C., Berger, S., <i>et al</i>. (2021) Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, 2391 p.
Nerem, R.S., Beckley, B.D., Fasullo, J.T., Hamlington, B.D., Masters, D. and Mitchum, G.T. (2018) Climate-Change-Driven Accelerated Sea-Level Rise Detected in the Altimeter Era. <i>Proceedings of the National Academy of Sciences of the United States of America</i>, 115, 2022-2025. <br>https://doi.org/10.1073/pnas.1717312115
Cazenave, A. and Cozannet, G.L. (2014) Sea Level Rise and Its Coastal Impacts. <i>Earth</i><i>’</i><i>s</i> <i>Future</i>, 2, 15-34. <br>https://doi.org/10.1002/2013ef000188
Arias, P., Bellouin, N., Coppola, E., Jones, R., Krinner, G., Marotzke, J., <i>et al</i>. (2021) Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change; Technical Summary. Cambridge University Press, 33-144.
Saji, N.H., Goswami, B.N., Vinayachandran, P.N. and Yamagata, T. (1999) A Dipole Mode in the Tropical Indian Ocean. <i>Nature</i>, 401, 360-363. <br>https://doi.org/10.1038/43854
Du, Y., Xie, S., Huang, G. and Hu, K. (2009) Role of Air-Sea Interaction in the Long Persistence of El Niño-Induced North Indian Ocean Warming. <i>Journal</i> <i>of</i> <i>Climate</i>, 22, 2023-2038. <br>https://doi.org/10.1175/2008jcli2590.1
Xie, S., Hu, K., Hafner, J., Tokinaga, H., Du, Y., Huang, G., <i>et al</i>. (2009) Indian Ocean Capacitor Effect on Indo-Western Pacific Climate during the Summer Following El Niño. <i>Journal</i> <i>of</i> <i>Climate</i>, 22, 730-747. <br>https://doi.org/10.1175/2008jcli2544.1
Painter, S.C. (2020) The Biogeochemistry and Oceanography of the East African Coastal Current. <i>Progress</i> <i>in</i> <i>Oceanography</i>, 186, Article ID: 102374. <br>https://doi.org/10.1016/j.pocean.2020.102374
Zheng, C., Zheng, S., Feng, M., Xie, L., Wang, L., Zhang, T., <i>et al</i>. (2024) Interannual Variability of the East African Coastal Current Associated with El Niño-Southern Oscillation. <i>Journal</i> <i>of</i> <i>Climate</i>, 37, 4613-4631. <br>https://doi.org/10.1175/jcli-d-23-0563.1
Manyilizu, M., Penven, P. and Reason, C. (2016) Annual Cycle of the Upper-Ocean Circulation and Properties in the Tropical Western Indian Ocean. <i>African</i> <i>Journal</i> <i>of</i> <i>Marine</i> <i>Science</i>, 38, 81-99. <br>https://doi.org/10.2989/1814232x.2016.1158123
Swallow, J.C., Schott, F. and Fieux, M. (1991) Structure and Transport of the East African Coastal Current. <i>Journal</i> <i>of</i> <i>Geophysical</i> <i>Research</i>: <i>Oceans</i>, 96, 22245-22257. <br>https://doi.org/10.1029/91jc01942
Semba, M., Lumpkin, R., Kimirei, I., Shaghude, Y. and Nyandwi, N. (2019) Seasonal and Spatial Variation of Surface Current in the Pemba Channel, Tanzania. <i>PLOS</i> <i>ONE</i>, 14, e0210303. <br>https://doi.org/10.1371/journal.pone.0210303
Bai, L., Zhu, G., Huang, H., Zhang, L., LÜ, H. and Zhang, Y. (2024) Characteristics of Mesoscale Eddies in the Mozambique Channel. <i>PLOS</i> <i>ONE</i>, 19, e0302367. <br>https://doi.org/10.1371/journal.pone.0302367
Gill, A.E., Green, J.S.A. and Simmons, A.J. (1974) Energy Partition in the Large-Scale Ocean Circulation and the Production of Mid-Ocean Eddies. <i>Deep</i> <i>Sea</i> <i>Research</i> <i>and</i> <i>Oceanographic</i> <i>Abstracts</i>, 21, 499-528. <br>https://doi.org/10.1016/0011-7471(74)90010-2
Smith, K.S. (2007) The Geography of Linear Baroclinic Instability in Earth’s Oceans. <i>Journal</i> <i>of</i> <i>Marine</i> <i>Research</i>, 65, 655-683. <br>https://doi.org/10.1357/002224007783649484
