The working of the IGRF 2000 Task Force

Abstract

At its meeting in July 1999, the IAGA Working Group for Analysis of the Global and Regional Geomagnetic Field and Secular Variation (WG V-8) felt unable to decide on a main-field model to use for IGRF 2000. It therefore set up a small Task Force with the remit to produce a model by the end of the year. This paper is the Chairman's report of the working of that Task Force, outlining the various stages involved, and giving the background to the various decisions. He also makes some retrospective personal comments.

Evaluation of the candidate Main Field model for IGRF 2000 derived from preliminary Ørsted data

“…1 (and other evidence, see for example Olsen et al (2000), and Lowes (2000)) suggested that the model and/or the Ørsted data did have some puzzling features, these were all of small magnitude. As a result of the numerical comparisons of this paper, and of other considerations reported in Lowes (2000), the Task Force decided that the tested model was good enough to be accepted as IGRF 2000.…”

“…However it was hoped that the apparent problems with the vector data from the Ørsted satellite would be overcome soon, and a small Task Force was set up to produce IGRF 2000 to a deadline. As reported in Lowes (2000), the final candidate model considered by the Task Force was in fact based on Ørsted vector and scalar data. This paper reports on the numerical assessment of this final candidate model, done by comparing it with independent recent measurements.…”

International Geomagnetic Reference Field—the eighth generation

“…As none of these four main-field models was deemed sufficiently accurate for an IGRF model (Macmillan, 2000;Mandea and Langlais, 2000) and because of the successful launch and operation of the Ørsted satellite after the submission deadline, it was decided at the XXII General Assembly of the International Union of Geodesy and Geophysics held in Birmingham (UK) in July 1999 to set up a Task Force to produce and evaluate a new IGRF main-field candidate model for 2000.0 based on Ørsted data. The operation of the Task Force is summarised by Lowes (2000), details of the derivation of this model are given in Olsen and Sabaka (2000) and of its evaluation by Lowes et al (2000). For the secular-variation model for 2000.0-2005.0 the three new candidate models were each given equal weight in the final model as there was insufficient evidence to recommend one model over another.…”

Use of Ørsted scalar data in evaluating the pre-Ørsted main field candidate models for the IGRF 2000

“…The fact that the Ørsted satellite was flying at the time of this Working Group meeting, gave the geomagnetic community the hope to get a new and better model to be adopted as IGRF 2000. This hope was achieved in November 1999 (Lowes, 2000;Olsen et al, 2000).…”