Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

The origin of geomagnetic jerks


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 analysis7), 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 surface8). 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 grounds9, and observed in both core flow models10 and numerical dynamo models11.

This is a preview of subscription content, access via your institution

Relevant articles

Open Access articles citing this article.

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: The secular variation (first derivative) of the magnetic field observed at Niemegk observatory (left; Germany) and at Macquarie Island observatory (right; south of Australasia).
Figure 2: The time-dependent part of the flow model (after removing the time average) from 1957 to 2001.
Figure 3: The spatially averaged power of the flow model from 1957 to 2001, compared with the one-, two- and three-wave fits to the flow model.


  1. Courtillot, V., Ducruix, J. & LeMouël, J.-L. Sur une accélération récente de la variation séculaire du champ magnétique terrestre. C. R. Acad. Sci. D 287, 1095–1098 (1978)

    Google Scholar 

  2. Malin, S., Hodder, B. & Barraclough, D. 75th Anniversay Volume of Ebro Observatory (ed. Cardus, J.) 239–256 (Roquetes, Tarragona, Spain, 1983)

    Google Scholar 

  3. Gavoret, J., Gilbert, D., Menvielle, M. & LeMouël, J.-L. Long-term variations of the external and internal components of the Earth's magnetic field. J. Geophys. Res. 91, 4787–4796 (1986)

    Article  ADS  Google Scholar 

  4. Gubbins, D. & Tomlinson, L. Secular variation from monthly means from Apia and Amberley magnetic observatories. Geophys. J. R. Astron. Soc. 86, 603–616 (1986)

    Article  ADS  Google Scholar 

  5. Macmillan, S. A geomagnetic jerk for the early 1990's. Earth Planet. Sci. Lett. 137, 189–192 (1996)

    Article  ADS  Google Scholar 

  6. Mandea, M., Bellanger, E. & LeMouël, J.-L. A geomagnetic jerk for the end of the 20th century? Earth Planet. Sci. Lett. 183, 369–373 (2000)

    Article  ADS  CAS  Google Scholar 

  7. Malin, S. & Hodder, B. Was the 1970 geomagnetic jerk of internal or external origin? Nature 296, 726–728 (1982)

    Article  ADS  Google Scholar 

  8. Waddington, R., Gubbins, D. & Barber, N. Geomagnetic field analysis—V. Determing steady core-surface flows directly from geomagnetic observations. Geophys. J. Int. 122, 326–350 (1995)

    Article  ADS  Google Scholar 

  9. Taylor, J. The magnetohydrodynamics of a rotating fluid and the Earth's dynamo problem. Proc. R. Soc. Lond. A 274, 274–283 (1963)

    Article  ADS  Google Scholar 

  10. Zatman, S. & Bloxham, J. Torsional oscillations and the magnetic field within the Earth's core. Nature 388, 760–763 (1997)

    Article  ADS  Google Scholar 

  11. Kuang, W. Force balances and convective state in the Earth's core. Phys. Earth Planet. Inter. 116, 65–79 (1999)

    Article  ADS  Google Scholar 

  12. Courtillot, V. & LeMouël, J. Geomagnetic secular variation impulses. Nature 311, 709–716 (1984)

    Article  ADS  Google Scholar 

  13. Roberts, P. H. & Scott, S. On the analysis of the secular variation, 1, A hydromagnetic constraint. Theory. J. Geomagn. Geoelectr. 17, 137–151 (1965)

    Article  ADS  Google Scholar 

  14. Bloxham, J. The steady part of the secular variation of the Earth's magnetic field. J. Geophys. Res. 97, 19565–19579 (1992)

    Article  ADS  Google Scholar 

  15. Bullard, E. C. & Gellman, H. Homogeneous dynamos and terrestrial magnetism. Phil. Trans. R. Soc. Lond. A 247, 213–278 (1954)

    Article  ADS  MathSciNet  Google Scholar 

  16. Davis, R. & Whaler, K. The 1969 geomagnetic impulse and spin-up of the Earth's liquid core. Phys. Earth Planet. Inter. 103, 181–194 (1997)

    Article  ADS  Google Scholar 

  17. Jackson, A. Time-dependency of tangentially geostrophic core surface motions. Phys. Earth Planet. Inter. 103, 293–311 (1997)

    Article  ADS  Google Scholar 

  18. Le Huy, M., Mandea, M., LeMouël, J.-L. & Pais, A. Time evolution of the fluid flow at the top of the core. Geomagnetic jerks. Earth Planets Space 52, 163–173 (2000)

    Article  ADS  Google Scholar 

  19. Zatman, S. & Bloxham, J. The Core-Mantle Boundary Region (eds Gurnis, M., Wysession, M., Knittle, E. & Buffett, B.) 183–196 (AGU Monograph, American Geophysical Union, Washington DC, 1998)

    Book  Google Scholar 

Download references


This work was supported by NSF and NASA. The authors thank A. Jackson and S. Macmillan for providing observatory data.

Author information

Authors and Affiliations


Corresponding author

Correspondence to Jeremy Bloxham.

Ethics declarations

Competing interests

The authors declare that they have no competing financial interests.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Bloxham, J., Zatman, S. & Dumberry, M. The origin of geomagnetic jerks. Nature 420, 65–68 (2002).

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI:

This article is cited by


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing