The Geomagnetic Spectrum For 1980 and Core-Crustal Separation

The spectrum of a high degree spherical harmonic model of the geomagnetic field is analysed to compute the constants for the core and crustal field contributions. Using a noise estimate of 0.091 nT2 at the mean Magsat radius of 6791 km, the power reduced to the Earth's surface is found to be 9.66 × 108 (0.286)n nT2 for the core, and 19.1 (0.996)n nT2 for the crust. These values show half the crustal power extrapolated to n = 0 compared with a previously published n = 23 model, and a white noise depth of only 14 km below the mean surface. the core spectrum power is 30 per cent less than previously estimated and becomes flat 80 km below the core-mantle boundary. the crustal power level is an eighth of that of an estimate based on one-dimensional analyses of Project MAGNET survey lines. the point where the energy density of the core and crustal components become equal at the Earth's surface is n = 14.2.