A large part of the Earth's magnetic field is generated by fluid motion in the molten outer core. Its temporal change, called secular variation, is characterized by occasional rapid changes known as geomagnetic jerks, sudden change in the second time derivative of the magnetic field. For a while, detailed studies of these phenomena suffered from the sparse distribution of geomagnetic observatories over many parts of the Earth. Recent studies on magnetic data provided by magnetic satellites, with a good global coverage, suggest that more rapid and smaller scale features than previously thought occur in the field change. Indeed, using nine years of magnetic field data obtained from CHAMP, Ørsted and SAC-C satellites as well as Earth-based observatories, the temporal changes in the core magnetic field and flow at the top of the core have been determined. Another approach has taken advantage of the high density of geomagnetic observatories in Europe to derive a regional model for detailed study of secular variation and acceleration over the past four decades. All known geomagnetic jerks are detected by this model; however, the time instant of a given jerk does not occur simultaneously in all magnetic field components. Both the regional and the global models indicate that secular variation and acceleration are very dynamic patterns suggesting short-term fluctuations and complex causal processes in the Earth's fluid core.
(2008): Rapid changes in the geomagnetic field: from global to regional scales
. AGU 2008 Fall Meeting. (San Francisco, USA 2008)