Physics
Scientific paper
Oct 1987
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987pepi...48..221w&link_type=abstract
Physics of the Earth and Planetary Interiors, Volume 48, Issue 3-4, p. 221-240.
Physics
11
Scientific paper
Geomagnetic records from some observatories give a strong indication that there was an extremely rapid, possibly impulsive, change in geomagnetic secular acceleration around 1969, and perhaps at other earlier epochs, which originated in the Earth's core. Controversy exists as to whether the change is indeed impulsive. A new application of a method of data analysis, which has been used extensively on palaeomagnetic demagnetisation data, is proposed to try to determine whether the impulsive model is viable, without a priori fixing the date of the `jerk'. The method is demonstrated on some of the biennial mean data of Malin and Hodder, although only ordered, rather than equally spaced, data are required. Statistical, and to some extent systematic, errors are taken into account. Some observatories satisfy the `jerk' hypothesis, i.e. the secular variation can be modelled as two straight lines intersecting at 1969. Others have one straight line segment either before or after the `jerk', but the sequence is more complex than just two straight lines. Secular variation at yet other observatories shows no linear structure at all. Evidence is found for a later emergence of the `jerk' at Australian observatories (which would be expected on Backus' theory). `Jerks' can be detected in any component of the field, regardless of which components have actually been measured; in fact, the method determines in which direction the `jerk' occurs, thereby offering the opportunity to improve the contour maps of the `jerk' made by Le Mouël et al.
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