Published: Vol. 144, Issue 2, February 2001.
Geophysical Journal International , 144, 471-480, 2001.

SUMMARY

The phase lag by which the earth's body tide follows the tidal potential is estimated for the principal lunar semidurnal tide M₂. The estimate results from combining recent tidal solutions from satellite tracking data and from Topex/Poseidon satellite altimeter data. Each data type is sensitive to the body-tide lag: gravitationally for the tracking data, geometrically for the altimetry. Allowance is made for the lunar atmospheric tide. For the tidal potential Love number k₂, we obtain a lag epsilon of 0.20° ± 0.05°, implying an effective body-tide Q of 280 and body-tide energy dissipation of 110 ± 25 gigawatts.

Key words: tides - earth tides - ocean tides - Love number - Q

By themselves neither satellite tracking data nor satellite altimeter data can distinguish an earth-tide lag from an ocean-tide lag. In combination, however, they may do so if each is sufficiently precise. For M₂ we find the lag in the earth's body tide to be 0.204° ± 0.047°. This represents so far the most direct and most precise determination of the effect of the earth's anelastic dispersion at half-daily periods. It stems from marked advances in both tracking and altimeter estimates. No comparably useful information about the lag in the load tide could be obtained.

Eventually one expects satellite geodetic constraints on anelasticity at a number of tidal periods. This has been accomplished for the 18.6 year tide, under the reasonable assumption that the ocean tide is in equilibrium with the generating potential and has no out-of-phase component (Eanes, 1995). Other long-period tides await improvements in the ocean models, especially in the data-sparse polar oceans where the P₂₀ function attains its maximum (e.g. Desai and Wahr, 1999). To some extent, the far Southern Ocean is also a limiting factor for diurnal tides - they all display an intense Antarctic Kelvin wave that noticeably contributes to P₂₁; the lunar tide O₁ appears to hold the most promise for the immediate future.

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Contact Richard Ray (rray@geodesy2.gsfc.nasa.gov) for further information or for a preprint of this paper.

Other links.
• Return to Richard Ray's web page.
• Global Geophysical Fluids Center, Special Bureau for Tides.