Earth rotation/polar motion excitations from atmospheric models

Author: David Salstein
December 1, 2004
Journal Article
Artificial Satellites

Salstein, D.A., 2004: Earth rotation/polar motion excitation from atmospheric models. Artificial Satellites, 35-46.

We review both the characteristics of the angular momentum signals that excite Earth rotation variations as calculated from global analyses of the atmosphere, as well as the ability of the current generation of global atmospheric models to simulate such signals. We are interested in results for the planetary axial component, whose fluctuations are related to length of day, and the two equatorial components, related to polar motion. Model results are compared with the analyses of the atmosphere that are produced by weather forecast centers, both contemporaneously and retrospectively, which are also known as operational analyses and reanalyses, repectively. Results from simulations by a group of atmospheric general circulation models forced by time-variable sea surface temperatures over a one- to two-decade period enable us to assess the current state-of-the-art in simulating atmospheric excitations of Earth rotation. These models have become increasingly skillful in this regard on both seasonal and interannual timescales, with much of the latter related to the dominant El Niño-Southern Oscillation atmosphere-ocean signal. Recently, some atmospheric general circulation models have also been run to simulate much of the last century. Several realizations of such a model for a period covering the 20th century, for example, have been used to estimate excitations of the Earth rotation on a number of time scales. Information from all these simulations of the past is useful in the design of atmosphere, or atmosphere-ocean coupled, models that can serve as tools to forecast the future, including those with scenarios of projected increases in greenhouse gases; such models could produce changes in Earth rotation or polar motion parameters.