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
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