MHD Sources, 1600-2005 Evolution and 1900-2005 Probabilistic Time Analysis for Logarithmic Time-Derivatives of Geomagnetic Spherical Harmonics

Abstract

MHD sources of geomagnetic spherical harmonics are estimated via logarithmic time derivatives (or exponential rates) of Gauss components basing on IGRF and gufm1 models. 1600–2005 rates’ evolutions show long flat ‘quiet’ and short pick-shaped ‘disturbed’ fields. Our probabilistic time analysis identifies the probabilities to grow/decay, expected values for grow/decay and median rates together with periodicity/aperiodicity estimates. Total grow/decay variations are ~20 years and median variations are ~100 years with variation as an inverse rate. Since 1900, the quiet field has grow/decay variations ~30 years while disturbed fields’ grow/decay variations ~10 years. The median variations are ~60 years for disturbed field and ~200 years for quiet one.