Earth rotation and global change

Abstract

Variations in the rotation of the Earth include changes in the rate of rotation (altering the Length of the Day, LOD), in orientation of the rotation axis relative to a terrestrial frame (Polar Motion, PM) and in orientation relative to a celestial frame due to external torques (Nutation and Precession). Variations occur over a wide range of time scales, from hours to the age of the Earth. Scientific interest in and understanding of Earth rotation variations have proceeded rapidly over the last several decades due, in large part, to enormous improvements in observations by space geodetic means, including satellite laser ranging (SLR), very long baseline interferometry (VLBI), lunar laser ranging (LLR), and satellite positioning methods, especially the global positioning system (GPS). The study of the Earth's rotation is a mature interdisciplinary field, and extensive reviews of many aspects of the field are contained in the AGU monographs ‘Contributions of Space Geodesy to Geodynamics’ (Smith and Turcotte, 1993). Articles by Eubanks (1993), Dickey (1993), Hide and Dickey (1991), and monographs by Lambeck (1988,1980) and Munk and Mac Donald (1960) provide excellent background material on these problems, as well. The reader may also wish to review other IUGG Report articles in this series on related subjects, specifically those on the global gravity field, VLBI technology, satellite orbit dynamics, and GPS.