B. Fong Chao

Atmospheric Excitation of the Earth's Annual Wobble' 1980-1988

Global meteorological analyses from the European Centre for Medium Range Weather Forecasts are employed to compute the atmospheric excitation Ψ of the polar motion for the 9-year period of 1980–1988. Both the matter component Ψ(matter) and the motion component Ψ(motion) are computed, the former with and without the oceanic inverted barometer (IB) effect. It is found that Ψ(motion) contributes significantly to the total excitation Ψ overall and nonnegligibly to the annual signal in Ψ, or the annual wobble excitation, in particular. Our results for the annual wobble excitation, in terms of the prograde component Ψ+ and the retrograde component Ψ− for January 1, are Ψ+ = (16.8 milliarc seconds (mas), −93°) and Ψ− = (15.6 mas, −98°) with IB, and Ψ+ = (17.3 mas, −101°) and Ψ− = (28.1 mas, −112°) without IB. These results are within the (rather large) range of previous estimates. The IB effect has a small impact on Ψ+, whereas its impact on Ψ− is considerable. The (better determined) prograde components Ψ+ are then compared with that observed from the Lageos satellite laser ranging data: (17.3 mas, −61°). Although the amplitudes are nearly equal, large phase discrepancies exist between the atmospheric and this observed value. The resolution of this discrepancy awaits a better knowledge of the seasonal angular momentum budget of the Earths surface fluid elements.