Atmospheric and oceanic excitation of decadal‐scale Earth orientation variations

Abstract

The contribution of atmospheric wind and surface pressure and oceanic current and bottom pressure variations during 1949–2002 to exciting changes in the Earth's orientation on decadal timescales is investigated using an atmospheric angular momentum series computed from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis project and an oceanic angular momentum series computed from a near‐global ocean model that was forced by surface fluxes from the NCEP/NCAR reanalysis project. Not surprisingly, since decadal‐scale variations in the length of day are caused mainly by interactions between the mantle and core, the effect of the atmosphere and oceans is found to be only about 14% of that observed. More surprisingly, it is found that the effect of atmospheric and oceanic processes on decadal‐scale changes in polar motion is also only about 20% (x component) and 38% (y component) of that observed. Therefore redistribution of mass within the atmosphere and oceans does not appear to be the main cause of the Markowitz wobble. It is also found that on timescales between 10 days and 4 years the atmospheric and oceanic angular momentum series used here have very little skill in explaining Earth orientation variations before the mid to late 1970s. This is attributed to errors in both the Earth orientation observations prior to 1976 when measurements from the accurate space‐geodetic techniques became available and to errors in the modeled atmospheric fields prior to 1979 when the satellite era of global weather observing systems began.

The Global General Circulation of the Ocean Estimated by the ECCO-Consortium

“…Estimates of oceanic mass and velocity fields produced by ECCO have been used to interpret geodetic measurements of Earth's orientation in space and its variable gravity field, and to highlight the major role of ocean angular momentum variability in explaining observed polar motion (e.g., Gross et al, 2005;Ponte et al, 2001Ponte et al, , 2007a. Comparisons with the geodetic data provide entirely independent tests of the ECCO results.…”

Status and Prospects for Combined GPS LOD and VLBI UT1 Measurements

“…Daily averaged values are formed around the middle epochs 00:00 and 12:00 to match the respective geodetic LOD series epochs. OAM values come from the ECCO_kf049f_6hr model (Gross et al, 2005), also with four values daily; the same noon and midnight averaging has been applied. The LODS and (AAM + OAM) time series were compared over the period 21 August 2000 to 31 March 2006.…”

Earth’s Rotation: A Challenging Problem in Mathematics and Physics

“…It includes noticeable changes of amplitudes and phases of its main components (the Chandler wobble with an amplitude usually ranging from 100 to 200 las and the annual term with an amplitude nearby 100 las) as well as a long-term drift (BARKIN 2000a, b;SCHUH et al 2001). A thorough review can be found in, e.g., GROSS (2007). Whilst nutations arise from a mainly astronomical forcing, the free wobbles of the pole are excited mainly by geophysical processes, and are difficult to predict (CHAO and GROSS 1987;DICKEY et al 2002, GROSS et al 2005.…”

“…A thorough review can be found in, e.g., GROSS (2007). Whilst nutations arise from a mainly astronomical forcing, the free wobbles of the pole are excited mainly by geophysical processes, and are difficult to predict (CHAO and GROSS 1987;DICKEY et al 2002, GROSS et al 2005. For that reason, the solution for the forced PM is not derived analytically along with the nutations, but is computed from different equations using empirical time series providing the relevant excitation functions (GROSS 1992;BRZEZIŃ SKI 1992).…”