Geomagnetic jerks and rapid hydromagnetic waves focusing at Earth’s core surface

Abstract

Geomagnetic jerks are abrupt changes in the second time derivative—the secular acceleration—of Earth’s magnetic field that punctuate ground observatory records. As their dynamical origin has not yet been established, they represent a major obstacle to the prediction of geomagnetic field behaviour for years to decades ahead. Recent jerks have been linked to short-lived, temporally alternating and equatorially localized pulses of secular acceleration observed in satellite data, associated with rapidly alternating flows at Earth’s core surface. Here we show that these signatures can be reproduced in numerical simulations of the geodynamo that realistically account for the interaction between slow core convection and rapid hydromagnetic waves. In these simulations, jerks are caused by the arrival of localized Alfvén wave packets radiated from sudden buoyancy releases inside the core. As they reach the core surface, the waves focus their energy towards the equatorial plane and along lines of strong magnetic flux, creating sharp interannual changes in core flow and producing geomagnetic jerks through the induced variations in magnetic field acceleration. The ability to numerically reproduce jerks offers a new way to probe the physical properties of Earth’s deep interior.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Fig. 1: Observed and simulated geomagnetic jerks at Earth’s surface.
Fig. 2: Comparison of the CHAOS-6x5 geomagnetic field model and the Midpath simulation at Earth’s core surface.
Fig. 3: Hydromagnetic waves inside the core and magnetic field structure from the Midpath model.
Fig. 4: Statistics of jerk recurrence time.

Data availability

The data that support the findings of this study are available from the corresponding author on request.

Code availability

The numerical simulation code used to generate the results of this study is available from the corresponding author on request.

References

  1. 1.

    Brown, W., Mound, J. & Livermore, P. Jerks abound: an analysis of geomagnetic observatory data from 1957 to 2008. Phys. Earth Planet. Int. 223, 62–76 (2013).

    Article  Google Scholar 

  2. 2.

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

    Google Scholar 

  3. 3.

    Malin, S. R. C., Hodder, B. M. & Barraclough, D. R. in Scientific Contributions in Commemoration of Ebro Observatory’s 75th Anniversary (ed. Cardús, J. O.) 239–256 (Observatorio Del Ebro, 1983).

  4. 4.

    Lesur, V., Wardinski, I., Hamoudi, M. & Rother, M. The second generation of the GFZ reference internal magnetic model: GRIMM-2. Earth Planets Space 62, 765–773 (2010).

    Article  Google Scholar 

  5. 5.

    Finlay, C. C., Olsen, N., Kotsiaros, S., Gillet, N. & Tøffner-Clausen, L. Recent geomagnetic secular variation from Swarm and ground observatories as estimated in the CHAOS-6 geomagnetic field model. Earth Planets Space 68, 112 (2016).

    Article  Google Scholar 

  6. 6.

    Olsen, N., Mandea, M., Sabaka, T. J. & Tøffner-Clausen, L. CHAOS-2—a geomagnetic field model derived from one decade of continuous satellite data. Geophys. J. Int. 179, 1477–1487 (2009).

    Article  Google Scholar 

  7. 7.

    Chulliat, A. & Maus, S. Geomagnetic secular acceleration, jerks, and a localized standing wave at the core surface from 2000 to 2010. J. Geophys. Res. 119, 1531–1543 (2014).

    Article  Google Scholar 

  8. 8.

    Chulliat, A., Thebault, E. & Hulot, G. Core field acceleration pulse as a common cause of the 2003 and 2007 geomagnetic jerks. Geophys. Res. Lett. 37, L07301 (2010).

    Article  Google Scholar 

  9. 9.

    Chulliat, A., Alken, P. & Maus, S. Fast equatorial waves propagating at the top of the Earth’s core. Geophys. Res. Lett. 42, 3321–3329 (2015).

    Article  Google Scholar 

  10. 10.

    Torta, J. M., Pavón-Carrasco, F. J., Marsal, S. & Finlay, C. C. Evidence for a new geomagnetic jerk in 2014. Geophys. Res. Lett. 42, 7933–7940 (2015).

    Article  Google Scholar 

  11. 11.

    Braginsky, S. I. Short-period geomagnetic secular variation. Geophys. Astrophys. Fluid Dynam. 30, 1–78 (1984).

    Article  Google Scholar 

  12. 12.

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

    Article  Google Scholar 

  13. 13.

    Gillet, N., Jault, D., Canet, E. & Fournier, A. Fast torsional waves and strong magnetic field within the Earth’s core. Nature 465, 74–77 (2010).

    Article  Google Scholar 

  14. 14.

    Wicht, J. & Christensen, U. R. Torsional oscillations in dynamo simulations. Geophys. J. Int. 181, 1367–1380 (2010).

    Google Scholar 

  15. 15.

    Teed, R. J., Jones, C. A. & Tobias, S. M. The dynamics and excitation of torsional waves in geodynamo simulations. Geophys. J. Int. 196, 724–735 (2014).

    Article  Google Scholar 

  16. 16.

    Schaeffer, N., Jault, D., Nataf, H.-C. & Fournier, A. Turbulent geodynamo simulations: a leap towards Earth’s core. Geophys. J. Int. 211, 1–29 (2017).

    Article  Google Scholar 

  17. 17.

    Aubert, J., Gastine, T. & Fournier, A. Spherical convective dynamos in the rapidly rotating asymptotic regime. J. Fluid. Mech. 813, 558–593 (2017).

    Article  Google Scholar 

  18. 18.

    Aubert, J. Geomagnetic acceleration and rapid hydromagnetic wave dynamics in advanced numerical simulations of the geodynamo. Geophys. J. Int. 214, 531–547 (2018).

    Article  Google Scholar 

  19. 19.

    Cox, G., Livermore, P. & Mound, J. The observational signature of modelled torsional waves and comparison to geomagnetic jerks. Phys. Earth Planet. Int. 255, 50–65 (2016).

    Article  Google Scholar 

  20. 20.

    Wardinski, I., Holme, R., Asari, S. & Mandea, M. The 2003 geomagnetic jerk and its relation to the core surface flows. Earth Planet. Sci. Lett. 267, 468–481 (2008).

    Article  Google Scholar 

  21. 21.

    Silva, L. & Hulot, G. Investigating the 2003 geomagnetic jerk by simultaneous inversion of the secular variation and acceleration for both the core flow and its acceleration. Phys. Earth Planet. Int. 198–199, 28–50 (2012).

    Article  Google Scholar 

  22. 22.

    Gillet, N., Jault, D. & Finlay, C. C. Planetary gyre, time-dependent eddies, torsional waves and equatorial jets at the Earth’s core surface. J. Geophys. Res. 120, 3991–4013 (2015).

    Article  Google Scholar 

  23. 23.

    Dormy, E. & Mandea, M. Tracking geomagnetic impulses at the core–mantle boundary. Earth Planet. Sci. Lett. 237, 300–309 (2005).

    Article  Google Scholar 

  24. 24.

    Mandea, M. et al. Geomagnetic jerks: rapid core field variations and core dynamics. Space. Sci. Rev. 155, 147–175 (2010).

    Article  Google Scholar 

  25. 25.

    Aubert, J., Finlay, C. C. & Fournier, A. Bottom-up control of geomagnetic secular variation by the Earth’s inner core. Nature 502, 219–223 (2013).

    Article  Google Scholar 

  26. 26.

    Kloss, C. & Finlay, C. C. Time-dependent low-latitude core flow and geomagnetic field acceleration pulses. Geophys. J. Int. 217, 140–168 (2019).

    Article  Google Scholar 

  27. 27.

    Bardsley, O. P. & Davidson, P. A. Inertial–Alfvén waves as columnar helices in planetary cores. J. Fluid. Mech. 805, R2 (2016).

    Article  Google Scholar 

  28. 28.

    Dean, R. G. & Dalrymple, R. A. Water Wave Mechanics for Engineers and Scientists Vol. 2 (World Scientific, 1991).

  29. 29.

    Le Huy, M., Alexandrescu, M., Hulot, G. & Le Mouël, J.-L. On the characteristics of successive geomagnetic jerks. Earth Planets Space 50, 723–732 (1998).

    Article  Google Scholar 

  30. 30.

    Sabaka, T. J., Olsen, N. & Purucker, M. Extending comprehensive models of the Earth’s magnetic field with Oersted and CHAMP data. Geophys. J. Int. 159, 521–547 (2004).

    Article  Google Scholar 

  31. 31.

    Pinheiro, K. J., Jackson, A. & Finlay, C. C. Measurements and uncertainties of the occurrence time of the 1969, 1978, 1991, and 1999 geomagnetic jerks. Geochem. Geophys. Geosyst. 12, Q10015 (2011).

    Article  Google Scholar 

  32. 32.

    Pais, M. A., Alberto, P. & Pinheiro, F. J. G. Time-correlated patterns from spherical harmonic expansions: Application to geomagnetism. J. Geophys. Res. 120, 8012–8030 (2015).

    Article  Google Scholar 

  33. 33.

    Olsen, N. & Mandea, M. Rapidly changing flows in the Earth’s core. Nat. Geosci. 1, 390–394 (2008).

    Article  Google Scholar 

  34. 34.

    Gillet, N. in Geomagnetism, Aeronomy and Space Weather: A Journey from the Earth’s Core to the Sun (eds Mandea, M. et al.) Ch. 9 (International Association of Geomagnetism and Aeronomy, 2019).

  35. 35.

    Nakagawa, T. Effect of a stably stratified layer near the outer boundary in numerical simulations of a magnetohydrodynamic dynamo in a rotating spherical shell and its implications for Earth’s core. Phys. Earth Planet. Int. 187, 342–352 (2011).

    Article  Google Scholar 

  36. 36.

    Christensen, U. R. Geodynamo models with a stable layer and heterogeneous heat flow at the top of the core. Geophys. J. Int. 215, 1338–1351 (2018).

    Article  Google Scholar 

  37. 37.

    Holme, R. & de Viron, O. Geomagnetic jerks and a high-resolution length-of-day profile for core studies. Geophys. J. Int. 160, 435–439 (2005).

    Article  Google Scholar 

  38. 38.

    Lesur, V., Whaler, K. & Wardinski, I. Are geomagnetic data consistent with stably stratified flow at the core–mantle boundary? Geophys. J. Int. 201, 929–946 (2015).

    Article  Google Scholar 

  39. 39.

    Schaeffer, N. & Jault, D. Electrical conductivity of the lowermost mantle explains absorption of core torsional waves at the equator. Geophys. Res. Lett. 43, 4922–4928 (2016).

    Article  Google Scholar 

  40. 40.

    Holme, R. & de Viron, O. Characterization and implications of intradecadal variations in length of day. Nature 499, 202–204 (2013).

    Article  Google Scholar 

  41. 41.

    Fournier, A. et al. An Introduction to data assimilation and predictability in geomagnetism. Space Sci. Rev. 155, 247–291 (2010).

    Article  Google Scholar 

  42. 42.

    Aubert, J. Geomagnetic forecasts driven by thermal wind dynamics in the Earth’s core. Geophys. J. Int. 203, 1738–1751 (2015).

    Article  Google Scholar 

  43. 43.

    Fournier, A., Aubert, J. & Thébault, E. A candidate secular variation model for IGRF-12 based on Swarm data and inverse geodynamo modelling. Earth Planets Space 67, 81 (2015).

    Article  Google Scholar 

  44. 44.

    Thébault, E. et al. International geomagnetic reference field: the twelfth generation. Earth Planets Space 67, 79 (2015).

    Article  Google Scholar 

  45. 45.

    Pichon, G., Aubert, J. & Fournier, A. Coupled dynamics of Earth’s geomagnetic westward drift and inner core super-rotation. Earth Planet. Sci. Lett. 437, 114–126 (2016).

    Article  Google Scholar 

  46. 46.

    Buffett, B. A. Geomagnetic fluctuations reveal stable stratification at the top of the Earth’s core. Nature 507, 484–487 (2014).

    Article  Google Scholar 

  47. 47.

    Christensen, U. R., Wardinski, I. & Lesur, V. Timescales of geomagnetic secular acceleration in satellite field models and geodynamo models. Geophys. J. Int. 190, 243–254 (2012).

    Article  Google Scholar 

  48. 48.

    Schaeffer, N. Efficient spherical harmonic transforms aimed at pseudospectral numerical simulations. Geophys. Geochem. Geosyst. 14, 751–758 (2013).

    Article  Google Scholar 

Download references

Acknowledgements

J.A. acknowledges support from the French Programme National de Planétologie of CNRS/INSU, and from the Fondation Simone et Cino Del Duca of Institut de France (2017 research grant). This work was granted access to the HPC resources of S-CAPAD, IPGP, France, and to the HPC resources of IDRIS, CINES and TGCC under allocations A0020402122 and A0040402122 from GENCI. The results presented in this work rely on data collected at magnetic observatories. The authors thank the national institutes that support them and INTERMAGNET for promoting high standards of magnetic observatory practice (www.intermagnet.org). This is IPGP contribution 4011.

Author information

Affiliations

Authors

Contributions

J.A. designed the project, designed and carried out the numerical experiments and wrote the manuscript. C.C.F. processed the geomagnetic data, constructed the CHAOS-6x5 geomagnetic field model and led its comparison with the simulation results. J.A. and C.C.F. processed the results and discussed the manuscript.

Corresponding author

Correspondence to Julien Aubert.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Supplementary Figs, Tables and references

Supplementary Video 1

Hammer projection of the core surface radial secular geomagnetic acceleration the CHAOS-6x5 geomagnetic field model filtered at spherical harmonic degree 9 from 1999 to 2018.

Supplementary Video 2

Hammer projection of the core surface radial secular geomagnetic acceleration from the Midpath model, filtered at spherical harmonic degree 9, in the vicinity of the jerk event occurring at 0 yr.

Supplementary Video 3

Hammer projection of the core surface azimuthal flow acceleration (blue is westwards) from the Midpath model, in the vicinity of the jerk event occurring at time 0 yr.

Supplementary Video 4

Partial equatorial cut and meridional cut outside the tangent cylinder of the convective density anomaly (orange denotes lighter fluid) from the Midpath model in the vicinity of the jerk event occurring at time 0 yr.

Supplementary Video 5

Partial equatorial cut and meridional cut outside the tangent cylinder of azimuthal flow acceleration (blue is westwards) from the Midpath model in the vicinity of the jerk event occurring at time 0 yr.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Aubert, J., Finlay, C.C. Geomagnetic jerks and rapid hydromagnetic waves focusing at Earth’s core surface. Nat. Geosci. 12, 393–398 (2019). https://doi.org/10.1038/s41561-019-0355-1

Download citation

Further reading

Search

Sign up for the Nature Briefing newsletter for a daily update on COVID-19 science.
Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing