Cyclogeostrophic balance in the Mozambique Channel

Type Article
Date 2014-02
Language English
Author(s) Penven Pierrick1, 2, 3, Halo Issufo2, 4, Pous Stephane2, 3, 5, Marie Louis6
Affiliation(s) 1 : UBO, IFREMER, CNRS, Lab Phys Oceans,UMR 6523,IRD, Plouzane, France.
2 : Univ Cape Town, Dept Oceanog, ZA-7925 Cape Town, South Africa.
3 : Univ Cape Town, IRD, LMI ICEMASA, ZA-7925 Cape Town, South Africa.
4 : Univ Cape Town, Nansen Tutu Ctr Marine Environm Res, ZA-7925 Cape Town, South Africa.
5 : UPMC, Lab Oceanog & Climat Expt & Approches Numer, CNRS, UMR 7159,IRD,MHN, Paris, France.
6 : IFREMER, UBO,CNRS, Lab Phys Oceans,UMR 6523,IRD, Plouzane, France.
Source Journal Of Geophysical Research-oceans (0148-0027) (Amer Geophysical Union), 2014-02 , Vol. 119 , N. 2 , P. 1054-1067
DOI 10.1002/2013JC009528
WOS© Times Cited 28
Abstract 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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