Heaides echo sounding, the ocean\'s bathymetry is measured using satellite altim

Question

Heaides echo sounding, the ocean's bathymetry is measured using satellite altimetry provided that the shape of the Geoid is accurately known. a) What is the Geold? Explain its concept. b) What is the first approximation to the Geoid? e) What causes the long wavelength deviations of the Geoid from a reference ellipsoid, and how are these deviations called? d) Sketch the shape of the sea surface and the plumb line orientation over a deep trough in the ocean floor. Note: in class we saw this in the case of a seamount. 8) 110) Based on the stratification that you see at the red circles and at the blue square in the vertical section of density shown below, where do you expect weak or strong occan currents? Explain your answer.

Explanation / Answer

a)

Geoid: The equipotential surface of the Earth's gravity field which best fits, in a least squares sense, global mean sea level

The geoid is everywhere perpendicular to the pull of gravity and approximates the shape of a regular oblate spheroid (i.e., a flattened sphere). It is irregular, however, because of local buried-mass concentrations (departures from lateral homogeneity at depth) and because of differences in elevation between continents and seafloors. Mathematically speaking, the geoid is an equipotential surface; that is, it is characterized by the fact that over its entire extent the potential function is constant. This potential function describes the combined effects of the gravitational attraction of Earth’s mass and the centrifugal repulsion caused by the rotation of Earth about its axis. Because of the irregular mass distributions in Earth and the resultant gravity anomalies, the geoid is not a simple mathematical surface. It consequently is not a suitable reference surface for a geometric figure of Earth

b) The Mean sea level is the first approximate to geoid

c)

Density variation in the Mantle (Upper and Lower) will account for the longer wavelength geoid anomalies.   Variations in the height of the geoid with respect to the reference ellipsoid are known as Geoid anomalies

The longer wavelength anomalies are accredited to deeper sub-surface Mantle density variations caused by convection currents and geoid highs are often associated with active subduction zones where higher density continental crust over rides lower density oceanic crust

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