Geomagnetic secular change, 1964-1970, from satelliteFand observatoryX, Y,andZ

A global model of the geomagnetic secular change consisting of 195 internal spherical harmonic coefficients (SHC) has been derived. The coefficients (to degree n = 13 and order m = 13) were assumed to be constant over the interval 1964–1970. The data for the spherical harmonic analysis consisted of values of scalar intensity secular change computed from a recent Pogo model for 648 points at altitude 800 km and values of vector secular change computed from the annual means at 136 observatories. The root means of weighted squared residuals for were, respectively, 2.1, 3.9, 3.2, and 3.2 nT/yr (1 nT = 1 nanotesla, equivalent to 1 γ). A model of 80 SHC fitted to the same data fits the values almost as well but is less satisfactory for .