The Solar Torque — A Leak for the Angular Momentum of the Earth-Moon System
The tides in the terrestrial oceans raised by the Moon lead to a transfer of angular momentum from the rotation of the Earth into the orbit of the Moon. Likewise, the tides raised by the Sun transport angular momentum from the rotation of the Earth into the “orbit of the Sun”which is the orbit of the Earth around the Sun. Due to the smaller tidal constant [mass/(distance)3] of the Sun, the solar effect is smaller than the lunar one. More important is the difference in the measurable manifestations. Today our best values stem from observations of the lunar orbit (lunar laser ranging and stellar occultations by the Moon); therefore they purely represent the lunar part of the tidal interchange. In contrast, the deceleration of the Earth being caused by both effects, does contain the solar signal as well. Unfortunately, the Earth underlies many other influences and hence the terrestrial value is not as accurate as the lunar one. Consequently, the standard procedure consists in a theoretical estimate of the ratio к = lunar/solar torque. This is applied to the observed lunar torque in order to obtain the total torque acting on the Earth (except for non-tidal torques; see Volland, this Vol.). Finally, this “hybrid” torque is compared with the observed tidal or secular change in the Earth’s rotation — as accurately as it can be isolated from the manifold of changes.
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- Lambeck K (1980) The Earth’s variable rotation. Univ Press, Cambridge, Chap 10, Table 10.3 Mignard F (1982) Long time integration of the Moon’s orbit. In: Brosche P, Sündermann J (eds) Tidal friction and the Earth’s rotation II. Springer, Berlin Heidelberg New York, p 67Google Scholar
- Munk WH, MacDonald GJF (1960) The rotation of the Earth. Univ Press, Cambridge, p 200ff Sündermann J (1982) The resonance behaviour of the world ocean. In: Brosche P, Sündermann J (eds) Tidal friction and the Earth’s rotation II. Springer, Berlin Heidelberg New York Tokyo, p 165Google Scholar