Observing long-term FCR variation using Esashi extensometers

Details Observing long-term FCR variation using Esashi extensometers Observing long-term FCR variation using Esashi extensometers

Jan 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006jgeo...41..155p&link_type=abstract

Journal of Geodynamics, Volume 41, Issue 1-3, p. 155-163.

Astronomy and Astrophysics

Astronomy

Scientific paper

Long duration precise and stable tidal observations are recorded to detect the temporal variation of free core nutation (also called the fluid core resonance, FCR) parameters, so as to reveal geophysical and dynamical processes at the core mantle boundary (CMB) of the Earth. At Esashi Earth Tides Station of National Astronomical Observatory of Japan, the tidal admittance and the non-tidal signal are estimated from 17 years of records with three extensometer data. From the estimated admittances of diurnal tidal constituents, the FCR parameters are fitted. The obtained time series of FCR eigenperiod and quality factor show 10 11 years scale temporal variation. The range of the eigenperiod variation is several dozens sidereal days (s.d.). This phenomenon is validated and confirmed by the gravitational tidal observation of a co-located super-conducting gravimeter (SG) with the observation from 1992 to 2002. Overestimated atmospheric response, extra loading effects from the temporal variations of local rock properties and of ocean tidal constituents, as well as the flattening variation of the topography at CMB are suggested to be the possible mechanisms to cause the periodical variation of FCR parameters.

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