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The recent satellite magnetic missions, combined with high quality ground observatory measurements, have provided excellent data for main field modelling. Four different groups submitted seven main-field and eight secular-variation candidate models for IGRF-10. These candidate models were evaluated using several different strategies. Comparing models with independent data was found to be difficult. Valuable information was gained by mapping model differences, computing root mean square differences between all pairs of models and between models and the common mean, and by studying power spectra and azimuthal distributions of coefficient power. The resulting adopted IGRF main-field model for 2005.0, an average of three selected candidate models, is estimated to have a formal root mean square error over the Earth's surface of only 5 nT, though it is likely that the actual error is somewhat larger than this. Due to the inherent uncertainty in secular variation forecasts, the corresponding error of the adopted secular-variation model for 2005.0-2010.0, an average of four selected candidate models, is estimated at 20 nT/a.

The coefficients for the new 9th Generation International Geomagnetic Reference Field (IGRF) were finalized at the XXIII General Assembly of the International Union of Geophysics and Geodesy (IUGG), held in Sapporo, Japan, in July 2003. The IGRF is widely used as a mathematical representation for the Earth's magnetic field in studies of the Earth's deep interior, crust, and ionosphere and magnetosphere. It is the product of a collaborative effort between magnetic field modelers and the institutes involved in collecting and disseminating magnetic field data from observatories and surveys around the world and from satellites.

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On this occasion the selection of the IGRF for 2000 was left to a small Task Force. Before it was accepted by the Task Force as IGRF 2000, the final candidate model (a truncated version of Ørsted(10c/99)) was compared with a comprehensive set of independent surface and satellite data. The method, data selection, and results of this comparison are described.

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Based on the geomagnetic data from repeat stations and observatories, the spherical cap harmonic model of the geomagnetic field over East Asia was derived. The pole of the spherical cap is at 45°N and 105°E and the half-angle of the spherical cap is 45°. The maximum index of the spherical cap harmonic analysis is 12, giving the minimum wavelength of 1635 km. The root mean square deviation values of the spherical cap harmonic model are 122.8 (north component), 103.4 (east component) and 128.0 nT (vertical component). The geomagnetic charts of East Asia were drawn at epoch 1980.0 from the spherical cap harmonic model. Furthermore, the deviation of the spherical cap harmonic model from DGRF 1980 was calculated, and the corresponding contour charts were drawn. IntroductionThe variations of the geomagnetic field over East Asia in time and in space are controlled by the magnetic anomaly of East Asia. In the past, the Chinese researchers studied the magnetic field on the south half part of East Asia only based on the Chinese geomagnetic survey while the Russian one did the north half part only based on the geomagnetic survey of former Soviet Union and Mongolia. Today the researchers of the two countries may jointly analyse the geomagnetic field over East Asia based on geomagnetic survey of China, former Soviet Union and Mongolia and the research was supported by Institute of Geophysics, Chinese Academy of Sciences and IZMIRAN, Russian Academy of Sciences. A model of the geomagnetic field over East Asia was derived by applying spherical cap harmonic analysis and the corresponding magnetic charts have been drawn. Moreover, the difference of the model from DGRF 1980 was calculated and the corresponding contour charts have been drawn. DataThe three-component observations at epoch 1980.0 from the magnetic repeat stations and the observatories of East Asia, including 98 magnetic repeat stations of China, 100 magnetic repeat stations of former Soviet Union and Mongolia and 39 observatories of the whole area of East Asia, were used. In order to model the geomagnetic field over East Asia, we rejected data, according to the criteria AX = IXobs -XDGRF I > 500 nT the data with the deviation greater than 500 nT from DGRF 1980(Langel, 1991 were removed. In our spherical cap harmonic analyses the geomagnetic data from 220 observation points were used. The distribution of the geomagnetic repeat stations and observatories is shown in Fig. 1. It is a important research to use the geomagnetic data from China, former Soviet Union and Mongolia simultaneously to derive the model of the geomagnetic field over East Asia. It makes us understand the distribution of the geomagnetic field over these areas, in some detail. Spherical Cap Harmonic AnalysisThe geomagnetic components were expressed directly in terms of spherical cap coordinates (Haines, 1985): is the maximum of the index; gk'n and he are the model coefficients. The pole of the spherical cap is located at 45°N and 105°E; the half-angle of the spherical cap is 45°. The 220 observation p...

A new generation of the IZMST series (STM-space-time models based on data from observatories, POGS and Ørsted) was developed as a model of the main geomagnetic field from 1980.0 up to 2000.0. A set of the natural orthogonal components (NOCs) was used as the basic time functions. The NOCs were derived from data series from 23 observatories widely distributed on the globe. These series were extrapolated by hand from epochs 1997.