Earth Planets Space, Vol. 59 (No. 7), pp. 675-684, 2007
Aude Chambodut1,2, Céline Eymin3, and Mioara Mandea2
1Department of Applied and Industrial Mathematics, University of Potsdam, Postfach 60 15 53, D-14415 Potsdam, Germany
2GeoForschungsZentrum Potsdam, Telegrafenberg, D-14473 Potsdam, Germany
3Laboratoire de Géophysique Interne et Tectonophysique, Université Joseph Fourier, BP53, 38041 Grenoble Cedex 9, France
(Received October 6, 2006; Revised June 1, 2007; Accepted June 6, 2007; Online published July 20, 2007)
Rapid changes in the magnetic field characterised by an abrupt change in the secular variation have been named "secular variation impulses" or "geomagnetic jerks". Three of these events, around 1968, 1978 and 1990, occurred during the time-span covered by the comprehensive model CM4 (Sabaka et al., 2002, 2004). This model, providing the best temporal resolution between 1960 and 2002 as well as a fine separation of the different magnetic sources, can be used to study rapid phenomena of internal origin. In order to analyse these events all over the globe, synthetic time series were obtained from the CM4 model between 1960-2002. Geomagnetic jerks are detected here as a rapid movement of the zero isoline of the second field derivative. Analysis of the area swept out by this isoline as a function of time allows us to map the spatial extent of jerks though time, and to identify an event around 1985 that is localized in the Pacific area. At the core surface, we compute the fluid flows under the frozen-flux and tangentially geostrophic assumptions. The flows do not exhibit any special pattern at jerk times, but instead show a smooth temporal evolution over the whole time period. However, the mean amplitude of the dynamical pressure associated with these flows present maxima at each jerk occurrence and helps to confirm the identification of a jerk in 1985.
Key words: Geomagnetic jerks, magnetic models, core surface flows, core dynamics.