HR: 11:20h
AN: G21E-04    [PDF]
TI: Temporal Evolution of Atmospheric and Oceanic Excitation of Earth Orientation Variations During the Past 50 Years
AU: * Gross, R S
EM: Richard.Gross@jpl.nasa.gov
AF: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 United States
AU: Fukumori, I
EM: fukumori@jpl.nasa.gov
AF: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 United States
AU: Menemenlis, D
EM: Dimitris.Menemenlis@jpl.nasa.gov
AF: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 United States
AB: The Earth rotates about its axis once a day, but does not do so uniformly. Instead, the rate of rotation fluctuates by up to a millisecond per day, and the Earth wobbles as it rotates. The principle of conservation of angular momentum requires that changes in the rotation vector of the solid Earth must be manifestations of (a) torques acting on the solid Earth or (b) changes in the mass distribution within the solid Earth, which alter its inertia tensor. Angular momentum is exchanged between the solid Earth and the fluid regions (the underlying liquid metallic core and the overlying hydrosphere and atmosphere) with which it is in contact; concomitant torques are due to hydrodynamic or magnetohydrodynamic stresses acting at the fluid / solid Earth interfaces. Here, the principle of conservation of angular momentum is used to study the effect on the Earth's orientation of changes in the mass distribution and motion of the atmosphere and oceans that have occurred during the past 50 years. The winds and surface pressure fields of the NCEP/NCAR reanalysis project are used to model the time varying angular momentum of the atmosphere since 1949. The NCEP/NCAR reanalysis surface fluxes are also used to force a model of the global oceans. The time varying angular momentum of the oceans since 1949 is computed from the resulting oceanic currents and bottom pressure fields. The modeled atmospheric and oceanic angular momentum series are then compared to observed changes in the Earth's orientation. The agreement between the observed and modeled Earth orientation variations is shown to improve as the accuracy of the Earth rotation observations and atmospheric and oceanic models has improved during the past 50 years.
DE: 1223 Ocean/Earth/atmosphere interactions (3339)
DE: 1239 Rotational variations
SC: Geodesy [G]
MN: 2003 Fall Meeting