Livermore, P orcid.org/0000-0001-7591-6716 (2022) A taxonomy of simulated geomagnetic jerks. Geophysical Journal International, 231 (1). pp. 650-672. ISSN 0956-540X
Abstract
Geomagnetic jerks - abrupt changes in the acceleration of Earth’s magnetic field that punctuate geomagnetic records - have been richly documented over the past decades by taking advantage of the complementary strengths of ground observatory and satellite measurements. It has recently been proposed that these events originate from the interplay and time scale separation between slow convection and rapid hydromagnetic wave propagation in Earth’s outer core, with these latter waves playing a key role in the generation of jerk signals. To assess the generality of this explanation, here we analyse a catalog of 14 events obtained during a 14000 year long temporal sequence from a numerical geodynamo simulation that is the closest to date to Earth’s core conditions regarding time scale separation. Events are classified according to their dynamical origin and the depth at which they are triggered in the outer core. The majority of jerk events are found to arise from intermittent local disruptions of the leading-order force balance between the pressure, Coriolis, buoyancy and Lorentz forces (the QG-MAC balance), that leads to an inertial compensation through the emission of rapid, non-axisymmetric, quasi-geostrophic Alfvén waves from the region where this force balance is disrupted. Jerk events of moderate strength arise from the arrival at low latitudes at the core surface of hydromagnetic wave packets emitted from convective plumes rooted at the inner core boundary. As in an earlier simulation, these account well for jerk features that have recently been documented by satellite and ground observations. The more realistic timescales in the simulation reported here allow further details to be distinguished, such as multiple temporal alternations of geomagnetic acceleration pulses at low latitudes, long-range synchronisation of pulse foci in space and rapid longitudinal drift of these foci at the core surface. The strongest events in the catalog arise from disruption of the leading-order force balance near or at the core surface, from the combined influence of the arrival of buoyancy plumes and magnetic field rearrangement. The hydromagnetic waves that are sent laterally and downwards generate signals that clearly illustrate the presence of nearly synchronous ‘V-shaped’ magnetic variation patterns over a wide portion of Earth’s surface and also at mid to high latitudes, despite the source being confined to low latitudes at the core surface. Other well-known characteristics of strong geomagnetic jerks such as surges in the intensity of the secular variation and inflexions in the length-of-day variations are also reproduced in these events. Irrespectively of the event strength, our results support the hypothesis of a single physical root cause - the emission of magneto-inertial waves following a disruption of the QG-MAC balance - for jerks observed throughout the geomagnetic record.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © The Author(s) 2022. Published by Oxford University Press on behalf of The Royal Astronomical Society. This is an author produced version of an article published in Geophysical Journal International. Uploaded in accordance with the publisher's self-archiving policy. |
Keywords: | Dynamo: theories and simulations, satellite magnetics, Rapid time variations |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds) > Inst of Geophysics and Tectonics (IGT) (Leeds) |
Funding Information: | Funder Grant number European Space Agency 4000127193/19/NL/IA |
Depositing User: | Symplectic Publications |
Date Deposited: | 17 Jun 2022 15:44 |
Last Modified: | 25 Jul 2022 15:25 |
Status: | Published |
Publisher: | Oxford University Press |
Identification Number: | 10.1093/gji/ggac212 |
Related URLs: | |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:188094 |