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Assimilation of Altimeter Data into a Quasigeostrophic Model of the Gulf Stream SystemThe dynamical consequences of constraining a numerical model with sea surface height data have been investigated. The model used for this study is a quasigeostrophic model of the Gulf Stream region. The data that have been assimilated are maps of sea surface height obtained as the superposition of sea surface height variability deduced from the Geosat altimeter measurements and a mean field constructed from historical hydrographic data. The method used for assimilating the data is the nudging technique. Nudging has been implemented in such a way as to achieve a high degree of convergence of the surface model fields toward the observations. The assimilation of the surface data is thus equivalent to the prescription of a surface pressure boundary condition. The authors analyzed the mechanisms of the model adjustment and the characteristics of the resultant equilibrium state when the surface data are assimilated. Since the surface data are the superposition of a mean component and an eddy component, in order to understand the relative role of these two components in determining the characteristics of the final equilibrium state, two different experiments have been considered: in the first experiment only the climatological mean field is assimilated, while in the second experiment the total surface streamfunction field (mean plus eddies) has been used. It is shown that the model behavior in the presence of the surface data constraint can be conveniently described in terms of baroclinic Fofonoff modes. The prescribed mean component of the surface data acts as a 'surface topography' in this problem. Its presence determines a distortion of the geostrophic contours in the subsurface layers, thus constraining the mean circulation in those layers. The intensity of the mean flow is determined by the inflow/outflow conditions at the open boundaries, as well as by eddy forcing and dissipation.
Document ID
19970028201
Acquisition Source
Headquarters
Document Type
Reprint (Version printed in journal)
External Source(s)
doi:10.1175/1520-0485(1995)025<1130:AOADIA>2.0.CO;2
Authors
Capotondi, Antonietta (Massachusetts Inst. of Tech. Cambridge, MA United States)
Malanotte-Rizzoli, Paola (Massachusetts Inst. of Tech. Cambridge, MA United States)
Holland, William R. (National Center for Atmospheric Research Boulder, CO United States)
Date Acquired
September 6, 2013
Publication Date
June 1, 1995
Publication Information
Publication: Journal of Physical Oceanography
Publisher: American Meteorological Society
Volume: 25
Issue: 6
Subject Category
Oceanography
Report/Patent Number
NASA-CR-205501
NAS 1.26:205501
Accession Number
97N27034
Funding Number(s)
CONTRACT_GRANT: NAGw-2711
CONTRACT_GRANT: JPL-958208
Distribution Limits
Public
Copyright
Public Use Permitted.

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