Decadal and Subdecadal Secular Variation of Main Geomagnetic Field

Summary

We present a preliminary study of the secular variation over the period 1980 – 2000. We are motivated by the fact that this time span is bookended by high-quality satellite vector data from Magsat in 1980 and Oersted and CHAMP in 1999 – 2001. For the intervening period we consider annual means of permanent magnetic observatories, to model secular variation and the main field. We use the field model to examine the geomagnetic jerk of 1991. It is important to understand how such a discontinuous feature should be modeled in the framework of optimally smooth models. Therefore we analysed the 1970 jerk by deterministic modeling of transient behaviour of the Y component of a single observatory. The results suggest a significant contribution from external field sources to the jerk—signal. Our global model gives separation of internal and external sources, and so will allow better characterization of the origin of the jerk.