Report from the IUGG Assembly: IAGA session on mathematical and physical aspects of modeling the geomagnetic field and its secular variation

Abstract

The session covered three broad topics: (a) techniques and practical modeling of the present geomagnetic field and its recent secular change; (b) spectral analysis of several geomagnetic time series; and (c) studies relating to the earth's deep conductivity and motions at the core boundary.Yukatake showed that higher‐frequency components remain after removal of trend and the solar cycle effect, and hence secular acceleration should be taken into account. In developing his simple method for evaluating models from scalar intensity data, James showed that, for an infinite series, two models may be derived, having an arbitrary potential difference. Barker demonstrated that the uniform spatial coverage expected of Magsat data will permit the compilation of models to a very high order and degree, computational problems being eased by appropriate partitioning, which includes a large measure of orthogonalization. He further reported on the joint U.S.A./U.K., 1 2th‐order main field model for 1980, derived from angular data only. The corresponding secular change model, using observatory repeat station service survey and satellite data, was reported by Malin, who also described the global morphology of the 1979 jerk.