ON ATMOSPHERIC-PRESSURE PERTURBATIONS ON PRECESSION AND NUTATIONS

The atmospheric pressure effects on the nutations are evaluated using the analytical expression of the rotational motion of the Earth in ine rtial space as a function of the external surface pressure torque. The most efficient term in perturbing the nutations is the S-1 solar baro metric tide of thermal origin; this wave induces a contribution to the prograde annual nutation but seasonal modulations of S-1 may also cau se perturbations to other nutations. Two extreme cases of oceanic resp onse to pressure fluctuations are considered (inverted barometer ocean or non-inverted barometer ocean) and various kinds of figures (ellips oid, geoid, topography) are introduced in the pressure torque computat ion. According to the forcing amplitude of the pressure field and to v arious assumptions in the torque computation, we obtain contributions to the nutation values ranging from a few tenths of a milliarcsecond u p to several milliarcseconds for the semi-annual and annual terms. Thi s shows the importance of atmospheric pressure corrections which have been ignored until now in the theoretical expressions of nutations as well as in the set of corrections applied to the observed nutations.