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Journal Articles Journal of Geophysical Research. Oceans Year : 2014

Cyclogeostrophic balance in the Mozambique Channel


Three methods are proposed for the inclusion of inertia when deriving currents from sea surface height (SSH) in the Mozambique Channel: gradient wind, perturbation expansion, and an iterative method. They are tested in a model and applied to satellite altimetry. For an eddy of 25 cm amplitude and 100 km radius, typical of Mozambique Channel rings at 18°S, the error made with geostrophy is 40% for the anticyclones and 20% for the cyclones. Inertia could reach one third of the pressure gradient. Geostrophy underestimates subsurface currents by up to 50 cm s−1, resulting in errors of 30–40%. The iterative method results in errors of <5% for the most part of the structure. The error RMS in velocities based on 8 years of model SSH is in excess of 30 cm s−1 for geostrophy and reduces to about 10 cm s−1 for the gradient wind and iterative methods. The perturbation method is less accurate. Applied to satellite altimetry, the addition of inertia results in a significant increase in velocities for the anticyclones and a decrease for the cyclones. It induces a velocity increase of >50% in Mozambique Channel rings. Geostrophic EKE reaches 1400 cm2 s−2, while it attains 1800 cm2 s−2 when inertia is added. Applied to the Gulf Stream, these methods confirm the hypothesis of Maximenko and Niiler [2006] that centrifugal accelerations should be the main cause for the difference observed between geostrophic and drifter EKE. This methodology should result in a net improvement for operational surface ocean currents.
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hal-01128387 , version 1 (03-01-2022)





Pierrick Penven, Issufo Halo, Stéphane Pous, Louis Marié. Cyclogeostrophic balance in the Mozambique Channel. Journal of Geophysical Research. Oceans, 2014, 119 (2), pp.1054-1067. ⟨10.1002/2013JC009528⟩. ⟨hal-01128387⟩
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