Comparing the jerk with other global models of the geomagnetic field from 1960 to 1978

Abstract

About 3300 satellite values of geomagnetic intensity and about 7000 observatory values of annual mean magnetic vector components from 1960 to 1978 were fitted by three global models of the geomagnetic field B Each model includes a spatially constant external field whose time dependence is a constant plus another constant times the Dst index, and each model accepts a time‐independent station correction at each observatory. The time dependence of the internal Gauss coefficients is either cubic, quintic, or biquadratic (two independent quadratics, one before and one after January 1, 1970); and g01 also has an induced term proportional to the Dst index. The rms residual of the data fit is the same for the cubic and biquadratic models and insignificantly smaller for the quintic model. The quintic and biquadratic models have 1164 adjustable parameters, and the cubic has 1038. At a high level of significance the parameters of the best fitting biquadratic rule out a physical model for the magnetic impulse of 1969 in which the level surfaces of electrical conductivity in the lower mantle are approximately spherical, and also the radial magnetic field at the core‐mantle boundary goes from one quadratic time dependence to another in a year or less.