Decadal and subdecadal secular variation of the main geomagnetic field

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We propose to examine the detailed secular variation over the period 1980-2000. This will be achieved by simultaneous modelling of the main field and secular variation using all available data. The time interval is "bookended" by high-quality satellite vector data, from Magsat in 1980, and Orsted/CHAMP in 1999-2000. All available data will be examined for the intervening period, especially secular variation recorded at permanent magnetic observatories and by repeat surveys. Particular attention will be paid to a re-examination of POGS data, with an attempt to extract some vector information from this data. The models derived will be used in various scientific studies including 1) consideration of "geomagnetic jerks", 2) modelling of core-surface flow, and 3) examination of possible time dependence of the lithospheric field. They will also be appropriate for considering the influence of external magnetic fields. The study will be used as a springboard towards submitting candidate models for IGRF 2005, and DGRF 1995 and 2000.