Project

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Understanding planetary magnetic fields from theoretical, numerical and analogue models

Applicant Jackson Andrew
Number 165641
Funding scheme Project funding
Research institution Institut für Geophysik ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Geophysics
Start/End 01.10.2017 - 31.03.2021
Approved amount 600'000.00
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Keywords (2)

geomagnetic field; dynamo theory

Lay Summary (French)

Lead
Earth's magnetic field has been in existence for more than 3.5 billion years, almost all of Earth history, and yet we have only a rudimentary understanding of how it operates. This grant will look into more detail at the process, using physical laboratory experiments,
Lay summary
Cette subvention appuiera un vaste programme d'investigations sur le mécanisme par lequel la Terre génère son champ magnétique par le mouvement du fluide dans son noyau de métal liquide.

Nous effectuerons des expériences dans un récipient sphérique à rotation rapide dans lequel le sodium liquide est agité par des courants électriques. Nous allons mesurer les mouvements de fluide résultant et les potentiels électriques, et surtout, les champs magnétiques résultants.

L'objectif général est de découvrir comment se déroule la compétition entre la rotation rapide et les champs magnétiques forts.
Direct link to Lay Summary Last update: 25.03.2017

Responsible applicant and co-applicants

Employees

Publications

Publication
The Surface Expression of Deep Columnar Flows
Holdenried‐Chernoff D., Maffei S., Jackson A. (2020), The Surface Expression of Deep Columnar Flows, in Geochemistry, Geophysics, Geosystems, 21(6), e2020GC009-e2020GC009.
A trio of simple optimized axisymmetric kinematic dynamos in a sphere
Holdenried-Chernoff D., Chen L., Jackson A. (2019), A trio of simple optimized axisymmetric kinematic dynamos in a sphere, in Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 475(2229), 20190308-20190308.

Associated projects

Number Title Start Funding scheme
199996 Statistical Properties of the Outer Core's Flow from Stochastic Geodynamo Models 01.09.2021 Early Postdoc.Mobility
163163 Low viscosity and no viscosity fluid dynamics in Earth's core 01.10.2015 Project funding

Abstract

The emphasis of the Earth and Planetary Magnetism group led by PI is to understand the generation and evolution of Earth's magnetic field. We carry out a broad suite of investigations ranging from data analysis from satellites and observatories to numerical simulations of the underlying physical equations and finally to laboratory experiments. Each facet plays a role in understanding the field of the Earth; the latter aspects are applicable to planets in general,and they are based on understanding the fundamental physics of rapidly rotating fluids in the presence of magnetic fields.In our quest to understand the generation of planetary magnetism through motional induction in electrically conducting fluids, a number of laboratories around the world have built spherical liquid sodium experiments that capture the main dynamics of planetary cores, namely rapid rotation and strong magnetic fields. These experiments are capable of working in regimes that are not accessible through numerical simulation. Our group has developed a unique rapidly rotating liquid metal experiment, SpiNaCH, capable of reproducing the planetary like conditions of dominant rotation and magnetic forces, the so-called magnetostrophic balance. Under these conditions the main goal is to understand how an internal magnetic field is generated from interior fluid flows and how the kinetic and magnetic energy finally dissipate in the system. Here we describe an approach to understanding planetary magnetism that focuses on the experimental approach.Our unified approach is based on the development and operation of the SpiNaCH experiment, while liaising withour other numerical approaches. Our numerical approaches have recently expanded to allow us to perform data assimilation, a technique whereby data can be assimilated into a numerical model of the underlying dynamicsof the system. Such approaches allow one, in general, to learn about features of the model, often termed ``state variables'', that are otherwise hidden from view.This proposal seeks to support one postdoctoral fellow and two PhD students who will focus their activities on the SpiNaCH platform. In addition, a critical element of the proposal is the partial support of a mechatronic engineer who is responsible for the systems of safety, control and data acquisition for the system. The science activities are focused on understanding the rapidly-rotating regime of fluid mechanics in the presence of sizable magnetic fields, wherebyCoriolis forces and Lorentz forces play a zeroth-order role; this regime is often termed ``magnetostrophic''.We wish to understand the behaviour in a real liquid metal, akin to that in a planetary core, that has a massive difference in viscous and magnetic diffusivities; this regime is extremely difficult to approach numerically because of the difference in the time scales and length scales involved. We wish to understand how mean flows are generated inthe experiment's interior, and discover how these flows compare to numerical predictions. The role of small scalefluid motion may appear naturally in the experiment, but there are also reasons to believe that small scales are suppressed by the action of the Coriolis and Lorentz forces; we wish to understand this. Small scales may give rise to so-called ``mean-field'' inductive effects, whereby electromotive forces are generated that are not described by the large-scale flows; again we wish to understand this behaviour. Some mean field effects give rise to an enhanced diffusivity of the fluid, and this has been measured occasionally in experiments around the world; we again seek tomeasure this phenomenon and understand it.In such a complex experiment, much of our activities are technical challenges and developments in methods of diagnosis; this is in addition to the huge engineering challenges that have largely been overcome but some of which still lie ahead.Novel approaches based on acoustic tomography using ultrasonic Doppler velocimetry and analysis of surface Hall probe and electrical potential data are key to our exploitation of the experiment. The deliverables from the two closely associated projects will be used to glean interior properties and dynamical regimes. Detailed comparisons will be made with numerical simulations that will be made in the regime that is as close as possible to the experimental regime.
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