An Estimate of Global Absolute Dynamic Topography

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  • 1 Center for Meteorology and Physical Oceanography, Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139
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Abstract

We estimate the absolute dynamic topography of the world ocean from the largest scales to a short-wavelength cutoff of about 6700 km for the period July through September 1978. The data base consisted of the time-averaged sea-surface topography determined by SEASAT and geoid estimates made at the Goddard Space Flight Center. The issues are those of accuracy and resolution. Use of the altimetric surface as a geoid estimate beyond the short-wavelength cutoff reduces the spectral 1eakage in the estimated dynamic topography from erroneous small-scale geoid estimates without contaminating the low wavenumbers. Comparison of the result with a similarly filtered version of Levitus' historical average dynamic topography shows good qualitative agreement. There is quantitative disagreement but it is within the estimated errors of both methods of calculation.

Abstract

We estimate the absolute dynamic topography of the world ocean from the largest scales to a short-wavelength cutoff of about 6700 km for the period July through September 1978. The data base consisted of the time-averaged sea-surface topography determined by SEASAT and geoid estimates made at the Goddard Space Flight Center. The issues are those of accuracy and resolution. Use of the altimetric surface as a geoid estimate beyond the short-wavelength cutoff reduces the spectral 1eakage in the estimated dynamic topography from erroneous small-scale geoid estimates without contaminating the low wavenumbers. Comparison of the result with a similarly filtered version of Levitus' historical average dynamic topography shows good qualitative agreement. There is quantitative disagreement but it is within the estimated errors of both methods of calculation.

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