Abstract
Geomagnetic secular variation, the generally slow, continuous change in the core magnetic field, is characterized by occasional rapid variations known as geomagnetic jerks. Recent studies on magnetic data obtained by satellites with a good global coverage suggest that more rapid and smaller scale features than previously thought occur in the field change. We have taken advantage of the comparatively high density of geomagnetic observatories in Europe and have derived a regional model for the detailed study of secular variation and acceleration over the past four decades from 1960 to 2001 by means of improved and regularized spherical cap harmonic analysis. We show the improvements to our regional model over a global model. All the known jerks are seen in our model, but further times with rapid changes in secular variation exist. Moreover, times of zero acceleration in general do not occur simultaneously in all magnetic field components, although this nearly is the case in 1969.6 and 1982.2. Secular variation and acceleration show very dynamic patterns indicating rapid and complex causal processes in the Earth’s fluid core.
Highlights
The geomagnetic field observed at the Earth’s surface contains components internal and external in origin
We show that rapid changes in the Secular variation (SV) and SA over Europe are well described by this new regional model
We have modeled the geomagnetic field changes over Europe for the past four decades by applying a regularized spherical cap harmonic analysis (SCHA) approach to the SV data series from 43 geomagnetic observatories
Summary
Higher spatial resolution can be obtained by local models when the magnetic field is described only over a given region of the Earth’s surface for which high density data exist Such regional models of the core field and its SV are commonly derived using Spherical Cap Harmonic Analysis, SCHA, (Haines, 1985) and improvements thereof. We have used the regularization proposed by Korte and Holme (2003) together with an improved (Verbanac, 2007) SCH regional modeling approach to investigate in detail the SV over Europe, the region covered most densely by geomagnetic observatories, for four decades (1961-2002) where several jerks had been identified in the east component time series (Alexandrescu et al, 1995; Macmillan, 1996; Mandea et al, 2000). We show that rapid changes in the SV and SA over Europe are well described by this new regional model
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