Some models of the geomagnetic field in western Europe from 1960 to 1980 |
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| Authors: | George Backus Sue Hough |
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| Institution: | Scripps Institution of Oceanography, University of California, San Diego, CA 92093 U.S.A. |
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| Abstract: | Achache et al.'s averages over 10 west European observatories of the annual mean magnetic components X, Y, Z are studied from 1953 to 1979. A 1970 jerk is fitted to the data by least squares, and the fit is quantitatively compared with that of a polynomial having the same number of free parameters as the jerk (a quintic). A crude correction for the 11-y sunspot cycle is also attempted. The jerk and quintic are equally good fits to X, the jerk is clearly better for Y, and the quintic is modestly better for Z. The jerk amplitudes of X and Z but not Y depend heavily on whether a sunspot correction is made, and such a correction may be required to estimate the energy of the internal part of the jerk in the manner of Malin and Hodder. The sunspot correction to Y probably cannot be brought above the noise because it is small and highly correlated with both the jerk and the quintic. The sunspot corrections to X and Z are statistically significant but depend on whether the core signal is taken as a jerk or a quintic. Courtillot and Le Mouël's physical model for the jerk predicts that the jerk amplitudes of X, Y, Z will be proportional to the longitudinal derivatives of X, Y and Z. This prediction is roughly verified for the magnitudes but not the signs; it is just possible that the signs in X and Z are not statistically significant. |
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