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Calculating the ocean's mean dynamic topography from a mean sea surface and a geoid

Bingham, R. J.; Haines, K.; Hughes, C. W.. 2008 Calculating the ocean's mean dynamic topography from a mean sea surface and a geoid. Journal of Atmospheric and Oceanic Technology, 25 (10). 1808-1822. 10.1175/2008JTECHO568.1

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Abstract/Summary

In principle the global mean geostrophic surface circulation of the ocean can be diagnosed by subtracting a geoid from a mean sea surface (MSS). However, because the resulting mean dynamic topography (MDT) is approximately two orders of magnitude smaller than either of the constituent surfaces, and because the geoid is most naturally expressed as a spectral model while the MSS is a gridded product, in practice complications arise. Two algorithms for combining MSS and satellite-derived geoid data to determine the ocean's mean dynamic topography (MDT) are considered in this paper: a pointwise approach, whereby the gridded geoid height field is subtracted from the gridded MSS; and a spectral approach, whereby the spherical harmonic coefficients of the geoid are subtracted from an equivalent set of coefficients representing the MSS, from which the gridded MDT is then obtained. The essential difference is that with the latter approach the MSS is truncated, a form of filtering, just as with the geoid. This ensures that errors of omission resulting from the truncation of the geoid, which are small in comparison to the geoid but large in comparison to the MDT, are matched, and therefore negated, by similar errors of omission in the MSS. The MDTs produced by both methods require additional filtering. However, the spectral MDT requires less filtering to remove noise, and therefore it retains more oceanographic information than its pointwise equivalent. The spectral method also results in a more realistic MDT at coastlines

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1175/2008JTECHO568.1
Programmes: Oceans 2025 > Climate, ocean circulation and sea level
ISSN: 0739-0572
Additional Information. Not used in RCUK Gateway to Research.: Copyright 2008 American Meteorological Society (AMS) Permission to use figures, tables and BRIEF excerpts from this work in scientific and educational works is hereby granted provided that is determined to be "fair use" under section 107 of the US Copyright Act or that it satisfies the conditions specified in 108 of the US copyright Act (17 USC Section 108 as revised by P.L. 94-553)does not require the AMS's permission. Or in a searchable database, or other uses of this material, except as exempted in the above statement, requires written permission or a license from the AMS. Additional details are provided in the AMS Copyright policy, available on the AMS website located at http://www.ametsoc.org/ or from the AMS at 617-227-2425 or copyright@ametsoc.org
Additional Keywords: GENERAL CIRCULATION;SATELLITE ALTIMETRY; GRAVITY FIELD; MODEL; REPRESENTATION; ACCURACY; GRACE; GOCE
NORA Subject Terms: Marine Sciences
Date made live: 13 Jan 2009 10:03
URI: http://nora.nerc.ac.uk/id/eprint/5369

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