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Discussion papers | Copyright
https://doi.org/10.5194/os-2018-51
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Technical note 23 May 2018

Technical note | 23 May 2018

Review status
This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Ocean Science (OS) and is expected to appear here in due course.

Technical Note: Two types of absolute dynamic ocean topography

Peter C. Chu Peter C. Chu
  • Naval Ocean Analysis and Prediction Laboratory, Department of Oceanography, Naval Postgraduate School, Monterey, CA 93943, USA

Abstract. Two types of marine geoid and the associated absolute dynamic ocean topography (referred as DOT) are presented. The first type is the average level of sea surface height (SSH) if the water is at rest (classical definition). The second type is determined by satellite observation under the condition that usually the water is not at rest. Its mean DOT (MDOT) is comparable to the first type DOT. Respective differences between the two geoids are that they exclude (include) the gravity anomaly and are non-measurable (measurable) in the first (second) type marine geoid. The first type DOT is determined by a physical principle that the geostrophic balance takes the minimum energy state. On the base of that, a new elliptic equation is derived for the first type DOT. Continuation of geoid from land to ocean leads to an inhomogeneous Dirichlet boundary condition with the boundary values taking satellite observed second-type MDOT. This well-posed elliptic equation is integrated numerically on 1° grids for the world oceans with the forcing function computed from the World Ocean Atlas (T, S) fields and the sea-floor topography obtained from the NOAA's ETOPO5 model. Between the first type DOT and second type MDOT, the relative root-mean square (RMS) difference (versus RMS of the first type DOT) is 38.6% and the RMS difference of the horizontal gradients (versus RMS of the horizontal gradient of the first type DOT) is near 100%. The standard deviation of horizontal gradients of DOT is nearly twice larger in the second type (satellite determined marine geoid with gravity anomaly) than in the first type (geostrophic balance without gravity anomaly). Such difference needs further attention from oceanographic and geodetic communities, especially the oceanographic representation of the horizontal gradients of the second type MDOT.

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Peter C. Chu
Peter C. Chu
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Short summary
A new concept of two types of marine geoid and associated absolute dynamic ocean topography is presented. The first type is the average level of sea surface height if the water is at rest (classical). The second type is determined by satellite observation under the condition that usually the water is in motion. The difference between the two types of absolute dynamic ocean topography is evident. Such difference needs attention from oceanographic and geodetic communities.
A new concept of two types of marine geoid and associated absolute dynamic ocean topography is...
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