Abstract
Abstract Following the call for candidates for the 10th generation IGRF, we produced and submitted three main field and three secular variation candidate models. The candidates are derived from parent models which use a standard quadratic parameterisation in time of the internal Gauss coefficients. External magnetospheric fields are represented by combined parameterisations in Solar Magnetic (SM) and in Geocentric Solar Magnetospheric (GSM) coordinates. Apart from the daily and annual variations caused by these external fields, the model also accounts for induction by Earth rotation in a non-axial external field. The uncertainties of our candidates are estimated by comparing independent models from CHAMP and Èrsted data. The root mean square errors of our main field candidates, for the internal field to spherical harmonic degree 13, are estimated to be less than 8 nT at the Earth’s surface. Our secular variation candidates are estimated to have root mean square uncertainties of 12 nT per year. A hind-cast analysis of the geomagnetic field for earlier epochs shows that our secular acceleration estimates from post-2000 satellite data are inconsistent with pre-2000 acceleration in the field. This could confirm earlier reports of a jerk around 2000.0, with a genuine change in the secular acceleration.
Highlights
The geomagnetic field at the Earth’s surface is strongly dominated by the long wavelength main field from the Earth’s core
The forecast of the secular variation is fraught with much larger uncertainties, estimated at 12 nT per year in 2007.5
This is partly caused by the chaotic behaviour of the field but may be due to a lack in our understanding of the true field dynamics
Summary
The geomagnetic field at the Earth’s surface is strongly dominated by the long wavelength main field from the Earth’s core. With the availability of more than five years of magnetic measurements from dedicated satellites (Ørsted, launched 1999 and CHAMP, launched 2000), combined with the long series of observatory measurements, the geomagnetic community currently has an excellent basis for deriving highly accurate main field models. Since it is not possible to estimate a sunsynchronous degree-2 external field from night side data alone, the external field was estimated from a combined CHAMP/Ørsted data set of the same period with full local time coverage. This magnetospheric field model was subtracted from the night side data before estimating the internal field.
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