M 2 ocean tide parameters and the deceleration of the Moon's mean longitude from satellite orbit data

An estimation has been made of the principal long‐period spherical harmonic parameters in the representation for the M 2 ocean tide from the orbital histories of three satellites: 1967–92A (Transit), Starlette, and Geos 3. The data used were primarily the evolution of the orbital inclinations of the satellites, with the addition of the longitude of the ascending node from Geos 3. The results are as follows: C 22 + = 3.42 ± 0.24 cm, ε 22 + = 325.5° ± 3.9°, C 42 + = 0.97 ± 0.12 cm, and ε 42 + = 124.0° ± 6.9°. These values agree quite well with recent numerical models and another recent determination from satellite data. Dissipational tidal friction in the oceans is known to provide the largest contribution to , the observed deceleration in the lunar mean longitude. Further, only the second‐degree components of the ocean tide contribute significantly to this secular decay (Lambeck, 1975). The M 2 parameters obtained here infer an of −25±3 arc sec/century 2 , in good agreement with other investigators. The range of current determinations of is from −24.6 to −27.2 arc sec/century 2 . Considerably different techniques have been used to derive the estimates: the study of ancient eclipses, transits of Mercury, lunar laser ranging, and another satellite solution.