Ronald H. Estes R.A. Langel L.A. Muth E.R. Benton 1982 <p>A two day selection of MAGSAT data is fit by spherical harmonic series truncated at increasing levels N_F in the range 2&lt;N_F&lt;14 to determine the extent to which the geomagnetic Gauss coefficients depend upon truncation level of the fit. The dependence is found to be concentrated in the range n&lt;N_F≲n+4 decreasing rapidly in magnitude to a few nanotesla as n increases to about 6.</p><p>Several geomagnetic properties are then examined by evaluating them at various truncation levels N with N_F fixed and N&lt;N_F. The spectrum of magnetic energy (outside the core and outside the earth) as determined by the N_F=23 MAGSAT model MGST 1/81 is evaluated. It suggests that the crustal anomaly contribution to magnetic energy outside the core will not exceed 0.1%, when the expansion is truncated at N=8. The positions of certain contours of the geomagnetic elements on the core-mantle boundary and their intersections needed for magnetic determination of the core motions, are examined and found to be relatively stable when N changes from 7 to 8, but to exhibit greater sensitivity for both larger and smaller values of N.</p><p>This article contains supplementary material.</p> application/pdf 10.1029/GL009i004p00254 en American Geophysical Union Sensitivity of selected geomagnetic properties to truncation level of spherical harmonic expansions article