Open AccessNon‐longitudinal drifts of the Earth's magnetic field
Author(s) -
Ostrowski Juliusz A.
Publication year - 1988
Publication title -
geophysical journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0952-4592
DOI - 10.1111/j.1365-246x.1988.tb01129.x
Subject(s) - equator , rotation (mathematics) , harmonics , amplitude , geodesy , earth's rotation , harmonic , magnetic dip , physics , secular variation , spherical harmonics , field (mathematics) , geology , geophysics , mathematics , latitude , geometry , optics , quantum mechanics , voltage , pure mathematics
SUMMARY Secular variation (SV) of the Earth's magnetic field has been represented by the non‐longitudinal drift (rotation about an arbitrarily oriented axis) and the amplitude change of the individual n th‐degree harmonics. The best‐fitting parameters have been obtained numerically for the separate harmonics of three field models at epoch 1968.0, and of one model at 1980.0. Formal error analysis showed that the effects of most of the rotations exceeded uncertainty levels due to the errors in the field model coefficients. Most of the well‐determined rotations were non‐longitudinal drifts with a predominant westward component. At 1968.0, rotation of about −0.23° yr −1 about an axis inclined at less than 25° to the equator accounted for about 80 per cent of the SV of the second harmonic. For the fourth harmonic, about 60 per cent of its SV was due to the rotation of −0.12° yr −1 about an axis inclined at about 44° to the equator. The results for 1980.0 were different: the rotation became most important for the fourth harmonic, accounting for 65 per cent of its SV, with the axis practically unchanged, but the rate doubled to −0.25° yr −1 . The axis for the second harmonic changed its inclination to 66°, drift rate rose to −0.27° yr −1 and the contribution of rotation decreased to about 55 per cent. Rotation of −0.14° yr −1 about an aids inclined 43° to the equator became significant for the third harmonic, contributing to over 60 per cent of its SV. The results for the 11th and 12th harmonics were distinctive. For POGO (02/72) model at 1968.0, they rotated with high velocities of 1.43° and 2.04° yr −1 about axes inclined at 38° and 58° to the equator; the rotation had a predominant eastward component. For GSFC (9/80) model, the 11th harmonic rotated almost westwardly with the rate increasing from −0.19° yr −1 at 1968.0 to −0.34° yr −1 at 1980.0; the results for the 12th harmonic were below the error level. The substantial changes in the secular variation of the lower harmonics and the distinctive behaviour of the highest harmonics of the POGO model are interpreted as an effect of the late‐1960s’ geomagnetic jerk—rapid change of the secular acceleration of the field. Present results, as well as geometry of the jerk, suggest that it can be roughly visualized as an anticlockwise rotational impulse in the field about a pole lying south of western Europe.