Statistical analysis and modeling of variations of the earth's magnetic field

Abstract

Power spectral analyses of the dipole moment of the earth's magnetic field inferred from ocean sediment cores and archeomagnetic data from time scales of 100 yr to 4 Myr have been carried out. The power spectrum is proportional to 1/f where f is the frequency. These analyses compliment previous work which has established a 1/f^2 spectrum for variations at time scales less than 100 yr. Power spectral analyses of inclination and declination inferred from lake sediments from time scales of 10 yr to 30 kyr have also been performed. The spectra are constant above time scales of 3 kyr, proportional to 1/f^2 from time scales of 500 yr to 3 kyr, and constant again below time scales of 500 yr. The 3 kyr time scale is associated with the decay time of the quadrupole moment. We test the hypothesis that reversals are the result of variations in dipole intensity with a 1/f spectrum which occasionally are large enough to cross the zero intensity value. Synthetic binormal time series with a 1/f power spectrum representing variations in the earth's dipole moment are constructed. Synthetic reversals from these time series exhibit statistics in good agreement with the reversal record. 1/f noise behavior is reproduced with a model of magnetic diffusion in the earth's core driven by dynamo action modeled as a random amplification or destruction of the local magnetic field.