STACKING GRAVITY TIDE MEASUREMENTS AND NUTATION OBSERVATIONS IN ORDERTO DETERMINE THE COMPLEX EIGENFREQUENCY OF THE NEARLY DIURNAL FREE WOBBLE

The resonance due to the nearly diurnal free wobble, observed in the d iurnal tesseral tides and in the associated nutations, is used to dete rmine the frequency and the damping of this wobble. The data are stack ed to provide a least squares estimation of the resonance parameters: frequency, quality factor, and complex strengths. Some previous papers presented the same kind of analysis using either tidal or nutation da ta sets; in both cases, the frequency was about -(1+1/435) cycle/sider eal day, but the quality factor was larger for nutation data than for tidal data. In this paper we analyze simultaneously both sets of data, and we focus our attention on the determination of the free core nuta tion period and quality factor. We have analyzed a series of tidal dat a sets provided by the International Center for Earth Tides (ICET), an d nutation data sets gathered from published matter. Our final result is obtained from a global stacking using four independent nutation dat a sets and three superconducting gravimeter data sets together. The va lues of the fitted parameters are found to be lambda(FCN) = -(1 + 1/(4 34.1 +/- 0.9)) cycle/sidereal day and Q congruent-to 54,000 (36,000; 1 09,000).