Long-term variations in the second sectorial Stokes harmonics on the basis of TOPEX/POSEIDON altimetry between 1993 and 2000 |
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| Authors: | M Burša S Kenyon J Kouba Z Šíma V Vatrt V Vítek M Vojtíšková |
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| Institution: | (1) Astronomical Institute, Acad. Sci. Czech Republic, Boční II/1401, 141 31 Praha 4, Czech Republic;(2) National Geospatial-Intelligence Agency, Arnold, MO 63010, USA;(3) Geodetic Survey Division, NRCan, 615 Booth Street, Ottawa, Canada, K1A OE9;(4) Geographical Service of the Czech Armed Forces, Military Geography and Hydrometeorology Office, Dobruška, Czech Republic;(5) Lipnická 1219, 39601 Humpolec, Czech Republic |
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| Abstract: | The long-term variations in the second degree sectorial Stokes parameters of the geopotential have been determined from TOPEX-POSEIDON
(T/P) satellite altimeter data, covering the period of January 1, 1993 to January 3, 2001 (T/P cycles 11-305). It is the first
attempt to determine the variations in the second sectorial harmonics in the Earth’s inertia tensor due to the ocean dynamics.
The variations amount to about 1 × 10−10 (J
2
(2)
≈ 1.6 × 10−6 and S
2
(2)
≈ −0.9 × 10−6). The variations are about 5% of the tidal effect. This corresponds to variations in the directions of the equatorial axes
of the Earth’s inertia ellipsoid of up to 10 arc-seconds. Consequently, the annual and semi-annual variations of the Earth’s
equatorial flattening is about 10−9; i.e. it corresponds to a change of 8 units of its denominator of 91 030. (The equatorial flattening ≈ 1/91 030).
Since the coverage of the Earth’s ocean surface is not worldwide, and the inclination of T/P is i = 66°, it is only 58.2%
(min. depth of the ocean 2 000 m) of the Earth’s surface which is processed, the torque, resulting from the seasonal transfer
of masses within a sea surface layer, is not zero. It amounts up to 1016 kg m2s−2, which is comparable to the total indirect tidal torque due to the Moon and the Sun, ∼ 3.9 × 1016 kg m2s−2. However, the above estimate strongly depends on the adopted thickness of the sea surface layer, ΔR = 50 m. For a larger
thickness of ΔR = 100 m, the seasonal torque amounts to about ∼ 2.3 × 1016 kg m2s−2. |
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| Keywords: | Earth’ s inertia tensor equatorial axes directions equatorial flattening variations T/P altimetry |
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