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1.
Determination of the free core nutation period from tidal gravity observations of the GGP superconducting gravimeter network 总被引:1,自引:1,他引:1
This study is based on 25 long time-series of tidal gravity observations recorded with superconducting gravimeters at 20 stations
belonging to the Global Geodynamic Project (GGP). We investigate the diurnal waves around the liquid core resonance, i.e.,
K
1, ψ1 and φ1, to determine the free core nutation (FCN) period, and compare these experimental results with models of the Earth response
to the tidal forces. For this purpose, it is necessary to compute corrected amplitude factors and phase differences by subtracting
the ocean tide loading (OTL) effect. To determine this loading effect for each wave, it was thus necessary to interpolate
the contribution of the smaller oceanic constituents from the four well determined diurnal waves, i.e., Q
1, O
1, P
1, K
1. It was done for 11 different ocean tide models: SCW80, CSR3.0, CSR4.0, FES95.2, FES99, FES02, TPXO2, ORI96, AG95, NAO99
and GOT00. The numerical results show that no model is decisively better than the others and that a mean tidal loading vector
gives the most stable solution for a study of the liquid core resonance. We compared solutions based on the mean of the 11
ocean models to subsets of six models used in a previous study and five more recent ones. The calibration errors put a limit
on the accuracy of our global results at the level of ± 0.1%, although the tidal factors of O
1 and K
1 are determined with an internal precision of close to 0.05%. The results for O
1 more closely fit the DDW99 non-hydrostatic anelastic model than the elastic one. However, the observed tidal factors of K
1 and ψ1 correspond to a shift of the observed resonance with respect to this model. The MAT01 model better fits this resonance shape.
From our tidal gravity data set, we computed the FCN eigenperiod. Our best estimation is 429.7 sidereal days (SD), with a
95% confidence interval of (427.3, 432.1). 相似文献
2.
Two long time series were analysed: the C01 series of the International Earth Rotation Service and the pole series obtained
by re-analysis of the classical astronomical observations using the HIPPARCOS reference frame. The linear drift of the pole
was determined to be 3.31 ± 0.05 milliarcseconds/year towards 76.1 ± 0.80° west longitude. For the least-squares fit the a priori correlations between simultaneous pole coordinates x
p
, y
p
were taken into account, and the weighting function was calculated by estimating empirical variance components. The decadal
variations of the pole path were investigated by Fourier and wavelet analysis. Using sliding windows, the periods and amplitudes
of the Chandler wobble and annual wobble were determined. Typical periods in the variable Chandler wobble and annual wobble
parameters were obtained from wavelet analyses.
Received: 21 January 2000 / Accepted: 28 August 2000 相似文献
3.
4.
Comparison of polar motion with oceanic and atmospheric angular momentum time series for 2-day to Chandler periods 总被引:2,自引:0,他引:2
J. Kouba 《Journal of Geodesy》2005,79(1-3):33-42
During a 4-year period starting in July 1996 and using intervals ranging from 3 days to 4 years, four precise polar motion (PM) series have been compared to excitation by atmospheric angular momentum (AAM) augmented with oceanic angular momentum (OAM) data. The first three series (C03, C04 and Bulletin A) are multi-technique combinations generated by the International Earth Rotation and Reference Systems Service (IERS) and the fourth combined series (IGS00P02) is produced by the International GPS Service (IGS) using only GPS data. The IGS PM compared the best with the combined excitations of atmosphere and oceans (AAM+OAM) at all intervals, showing high overall correlation of 0.8–0.9. Even for the interval of only three days, the IGS PM gave a significant correlation of about 0.6. Moreover, during the interval of February 1999 – July 2000, which should be representative of the current precision of the IGS PM, a significant correlation (>0.4) extended to periods as short as 2.2 days and 2.5 days for the xp and yp PM components, respectively. When using the IERS Bulletin B (C04) PM and an interval of almost 6 years, starting in November 1994, the combined OAM+AAM accounted for practically all the annual, semi-annual and Chandler wobble (CW) PM signals. When only AAM was used, either the US National Centers for Environment Prediction reanalysis data, which were used throughout this study, or the Japanese Meteorological Agency data, two large and well-resolved amplitude peaks of about 0.1 mas/day, remained at the retrograde annual and CW periods. 相似文献