Geomagnetism

Magnetic Field Model MF4xx:

MF4x is a lithospheric field model from CHAMP satellite data, estimated by a new algorithm from the same cleaned data set which was used for MF4. By using linear combinations of spherical harmonics (SH), we defined localized functions which are band-limited to a given maximum degree. Using these localized basis functions, a model's SH resolution can be varied over the globe. MF4x resolves features to SH degree 90 at low latitudes, but only to SH degree 60 in the Polar regions. This is illustrated in the comparison with MF4 in Figure 1. The new model can be downward continued from satellite altitude to the Earth's surface without generating spurious high-latitude anomalies.

Figure 1: The central column shows the vertical magnetic field component of the new model MF4x at the Earth's equatorial radius for a low latitude and the North and South Polar regions. For comparison, the left column shows MF4 in full resolution and the right column shows MF4 limited to SH degree 60. As designed, the new model has the full resolution of MF4 at low latitudes and is band-limited to SH degree 60 in the Polar regions.

Available MF4x Downloads
	Type	Format	Mbyte	Ref.Radius	Contents
	SH coefficients	ASCII Table	0.2		MF4x Model spherical harmonic coefficients (Schmid semi-normalized, as usual)
	Graphic	EPS	15	6379.2 km	Comparison of MF4/MF4x for equatorial and polar regions.
	Data grid	ASCII Listing	20	6379.2 km	Grid of Bz at the equatorial Earth radius (r=6379.2)
	Article	PDF	0.5		Manuscript submitted to GRL describing the model

2006-May-01, Vincent Lesur and Stefan Maus.