Open AccessThe nearly diurnal free wobble resonance in gravity measured at Cantley, Quebec
Author(s) -
Merriam J. B.
Publication year - 1994
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1111/j.1365-246x.1994.tb00129.x
Subject(s) - gravimeter , geodesy , geology , polar motion , speed wobble , range (aeronautics) , physics , atmospheric pressure , seismology , meteorology , geophysics , classical mechanics , materials science , composite material , casing , earth's rotation
SUMMARY Three years of data from the superconducting gravimeter at Cantley, Quebec, are inverted for the parameters of the Nearly Diurnal Free Wobble (NDFW). The parameters which characterize the phenomenon in gravity are found to be: period T = 430 days (427–434), real part of oscillator strength B r =−6.31 × 10 −4 (−6.40 × 10 −4 to −6.26 × 10 −4 ), imaginary part of oscillator strength B i = 3 × 10 −6 (−2 × 10 −5 to 2 × 10 −5 ), and Q = 7000 (5500–10 000). Ocean tide loading is estimated here from the gravity data, rather than from ocean tide models, because the latter are shown to be inadequate for this problem. The range of acceptable ocean tide load models used here is such that the uncertainty in the ocean load correction implies systematic errors in the NDFW parameters that are no larger than formal errors. It is shown that the catalogue used to determine the tidal admittances can seriously influence the NDFW parameters inverted from them, and in particular, the diversity of Q 's found in previous studies may be due in part to the use of an older catalogue. It is shown that atmospheric pressure has significant power at precisely the frequencies important to the measurement of the NDFW parameters, and that a careful correction for atmospheric pressure is required. The free motion itself is not detected, and it is unlikely that it will be seen in gravity measurements in the near future.