Use of Orsted scaler data in evaluating the pre-Orsted main field candidate models for the IGRF 2000

For describing the main field model at the 2000.0 epoch and the secular var iation over the 2000-2005 timespan, three candidate models for the Internat ional Geomagnetic Reference Field (IGRF 2000) were proposed at the beginnin g of 1999, called in alphabetical order IPGP00 (proposed by IPGP), IZMI00 ( proposed by IZMIRAN) and USUK00 (proposed by USGS/BGS). A fourth model, IGR F95 (the updated IGRF 1995), was suggested by the Working Group chairman. T he modelling methods and the data used are presented by each team elsewhere in this special issue. This study is an attempt to test these models using the total field intensity provided by the Orsted satellite, the only data available from that satellite at the time when the two tests describing her e were done. The first rest consists of evaluating the differences between the real and the synthetic data computed from the candidate models. The sec ond test compares the capability of the candidate models to reduce the Back us effect, using a predictive dip-equator position and Orsted data. Both te sts shaw that the quality of the candidate models is far from being accepta ble, and, therefore, a new candidate model for the main field, using vector ial Orsted data, is required.