RATES OF CHANGE OF THE EARTHS MAGNETIC-FIELD MEASURED BY RECENT ANALYSES

The availability of accurate representations of the Earth's magnetic field for the past 25 years allows us to study the typical rates of change of the field as a function of the degree of the spherical harmonic. It is shown that there is a general increase in the relative rate of change as the degree of harmonic is increased. The analysis was only carried out to degree eight harmonics, because knowledge of the rate of change of the higher degrees is poor. With knowledge only of degrees eight or less, little is found about longitudinal motions. Evidence for secular acceleration was found. Not surprisingly, the average rate of secular acceleration increased with the degree of harmonic, rising from 0.001°/yr2 for the dipole term to an average of 0.05°/yr2 for the degree eight harmonics. -from Authors