This data set consists of a set of subroutines designed to calculate the magnetic field of the Earth from -40 Earth radii to +10 Earth radii. The coefficients are calculated assuming the axis of the Earth's dipole is perpendicular to the Earth-Sun line. The magnetic potential was obtained by integrating over a model magnetotail current system and fitting the surface field to a set of Bessel functions.
D. B. Beard, The Magnetotail Magnetic Field, J. Geophys. Res. 84, 2118, 1979.