Open AccessRotation of the geomagnetic field about an optimum pole
Author(s) -
Bülent Tank S.
Publication year - 2000
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 - 10.1046/j.1365-246x.2000.00037.x
Subject(s) - earth's magnetic field , geodesy , rotation (mathematics) , secular variation , dipole , epoch (astronomy) , north pole , field (mathematics) , stochastic drift , geology , spherical harmonics , earth's rotation , physics , geophysics , geometry , magnetic field , mathematics , astrophysics , geography , statistics , quantum mechanics , pure mathematics , stars , physical geography
Since 1693, when Halley proposed that secular change was the result of the westward drift of the main field, his simple model has undergone many refinements. These include different drift rates for dipole and non‐dipole parts; separation into drifting and standing parts; latitudinal dependence of drift rate; northward drift of the dipole; and non‐longitudinal rotations of the individual harmonics of the geomagnetic field. Here we re‐examine the model of Malin and Saunders, in which the main field is rotated about an optimum pole which does not necessarily coincide with the geographical pole. The optimum pole and rotation angle are those that bring the main field for epoch T 1 closest to that for T 2 , as indicated by the coefficients of correlation between the spherical harmonic coefficients for the two epochs, after rotation. Malin and Saunders examined the pole positions and rates of rotation using data from 1910 to 1965, and noticed a number of trends. We show that these trends are confirmed by recent IGRF models, spanning the interval 1900–2000 and to degree and order 10. We also show that the effect of the level of truncation is small.