Publication Date:
2021-10-13
Description:
The space-borne geodetic temporal mean dynamic topography (MDT) is obtained from the difference of altimetric mean sea surface (MSS) h and the geoid height N. With the geostrophic surface currents obtained from its gradient, the MDT is an essential parameter when describing the ocean dynamics. Spectral consistency of h and N is crucial to minimize MDT errors. Frequently, h is globalized to allow for a spherical harmonic analysis, and small scales beyond maximum degree and order (d/o) resolved in the geoid are cut off. However, common globalization causes ocean-land steps in h−N and spectral inconsistencies of N and h over land. To overcome both issues, a methodology is proposed based on globalization of the MDT. A Laplacian smoother with the coastal MDT values as boundary condition is applied, resulting in a smooth surface over land and a continuous ocean-land transition. The new methodology strongly reduces Gibbs effects and the need to work with high-resolution MDTs to minimize them. Reduction of resolution is tested to reduce MDT uncertainties caused by the commission error expected to increase with decreasing scale. Applying drifter data and a high-resolution hydrodynamic ocean model, it is shown that for the Gulf Stream and the Kuroshio, geodetic MDTs applying recent combined geoid models contain physical information up to at least d/o 420 (48-km spatial scale). For oceanic regions with strong geoid gradients, a higher-resolution MDT might be needed to prevent Gibbs effects caused by remaining inconsistencies between the geoid and the MSS.
Keywords:
526.1
;
551.46
;
Mean Dynamic Topograhy
;
altimetry
;
geoid
;
spectral consistency
;
Gibbs effect
Language:
English
Type:
map
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