Cyclogeostrophic balance in the Mozambique Channel. Issue 2 (12th February 2014)

• Record Type: Journal Article
• Authors: Penven, Pierrick; Halo, Issufo; Pous, Stéphane; Marié, Louis
• Is Part Of: Journal of geophysical research. Volume 119:Issue 2(2014:Feb.)
• Page Start: 1054
• Page End: 1067
• Publication Date: 2014-02-12
• Subjects: Oceanography -- Periodicals; 551.4605
• DOI: 10.1002/2013JC009528
• Languages: English
• ISSNs: 2169-9275

Abstract

<abstract abstract-type="main"> <title>Abstract</title> <p>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<sup>−1</sup>, 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<sup>−1</sup> for geostrophy and reduces to about 10 cm s<sup>−1</sup> 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 cm<sup>2</sup> s<sup>−2</sup>, while it attains 1800 cm<sup>2</sup> s<sup>−2</sup> when inertia is added. Applied to the Gulf Stream, these methods confirm the hypothesis of <italic>Maximenko and Niiler</italic> [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.</p> </abstract>