Derivation of a geomagnetic model to n=63

SUMMARY A high degree model of the geomagnetic fielc is derived using an integral technique to extend coefficients beyond the limits allowable with least squares approaches. A previously derived model to n = 29 was first updated with new secular change data for the interval 1979 September-1980 June combined with the previously obtained analysis set of Magsat vector data. Residuals of a new selection of observed vector Magsat data were then analysed by solving for ionospheric-magnetospheric variations and removing their effect. The reduced B, components were then averaged over approximately 3” X 3” blocks of latitude and longitude, and coefficients derived using the Neumann method. These coefficients, when combined with those from the least squares solution, were seen to show significantly greater detail in the structure of the geomagnetic field which appeared to be realistic to n = 50.

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