The origin of geomagnetic jerks

Abstract

Geomagnetic jerks, which in the second half of the twentieth century occurred in 1969 (refs 1, 2), 1978 (refs 3, 4), 1991 (ref. 5) and 1999 (ref. 6), are abrupt changes in the second time-derivative (secular acceleration) of the Earth's magnetic field. Jerks separate periods of almost steady secular acceleration, so that the first time-derivative (secular variation) appears as a series of straight-line segments separated by geomagnetic jerks. The fact that they represent a reorganization of the secular variation implies that they are of internal origin (as has been established through spherical harmonic analysis), and their short timescale implies that they are due to a change in the fluid flow at the surface of the Earth's core (as has also been established through mapping the time-varying flow at the core surface). However, little is understood of their physical origin. Here we show that geomagnetic jerks can be explained by the combination of a steady flow and a simple time-varying, axisymmetric, equatorially symmetric, toroidal zonal flow. Such a flow is consistent with torsional oscillations in the Earth's core, which are simple oscillatory flows in the core that are expected on theoretical grounds, and observed in both core flow models and numerical dynamo models.

Geomagnetic secular variation violating the frozen-flux condition at the core surface

“…4). This is more or less consistent with the arguments of steady diffusion (Voorhies, 1993;Love, 1999) as well as with the arguments for the primary contribution of the advection to the geomagnetic jerks (Bloxham et al, 2002;Olsen and Mandea, 2008;Wardinski et al, 2008).…”

Decadal variability in core surface flows deduced from geomagnetic observatory monthly means

“…Whaler 1986). Bloxham et al (2002) found that a constant flow with TO superimposed provided a good fit to observatory SV; such a model requires just a few parameters. However, this conclusion was not based on an inversion of the observatory data themselves.…”

Geomagnetic intensity variations for the past 8 kyr: New archaeointensity results from Eastern China

“…Therefore, the behavior of geomagnetic field has significant potential to yield insight into Earth's geodynamics, such as the influence of core-mantle interactions Bloxham, 2000), changes in outer-core flow and geomagnetic jerks (Bloxham et al, 2002;Dumberry and Finlay, 2007;Mandea et al, 2010;Olsen and Mandea, 2008). Besides the geodynamic significance, connections between the geomagnetic field and global climate have been suggested (Courtillot et al, 2007;Gallet et al, 2005;Kent, 1982), but these claims remain controversial (Bard and Delaygue, 2008).…”