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The geomagnetic field over the last few thousand years: Measurements, models, and mechanisms

Applicant Jackson Andrew
Number 130147
Funding scheme Project funding
Research institution Institut für Geophysik ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Geophysics
Start/End 01.06.2010 - 30.09.2012
Approved amount 350'364.00
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Keywords (7)

archeomagnetism; geomagnetic field; data assimilation; Earth's core; archaeomagnetism; geomagnetic secular variation; magnetic field

Lay Summary (English)

Lead
Lay summary
We describe research aimed at elucidating the evolution of the magnetic field over the last 8000 years, focusing on short timescales (such as the last few decades, during which there is excellent data quality), medium timescales of hundreds of years (where actual magnetic field measurements are available), and long timescales (where archaeomagnetic data can be used). Our aim is to focus for the first time on 3-dimensional models of the magnetic field in the interior of the core, and to adopt a variational data assimilation technique to optimally fit the available data whilst honouring the relevant physics. In order to find the best possible models for the archaeomagnetic evolution of the field we describe data collection activities aimed at improving the database that is used to constrain the model.A minimal-physics dynamical evolution model for the Earth's core is used in conjunction with observations to find the initial conditions that lead to an evolution of the system best in accord with the observations. In order to discover this model we adopt a variational data assimilation technique, employing an adjoint model, to optimally solve the problem. Central to our creation of a time-varying model for the last 8000 years is the collection of new archaeomagnetic data to improve the temporal constraints available in Europe. Sites in Itay, Switzerland and Bulgaria present constraints over the period range 6000BC to 1100AD, which will be used in conjunction with the existing GEOMAGIA database of archaeomagnetic measurements.In addition we propose a major study of previouslyanalysed archaeomagnetic data from the United States. These data are in the form of demagnetisation curves, but require some effort to determine archaeo declinations, inclinations and ages.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Combining an archaeomagnetic and radiocarbon study: Dating of medieval fireplaces at the Muhlegasse, Zurich
Donadini F, Motschi A, Rosch C, Hajdas I (2012), Combining an archaeomagnetic and radiocarbon study: Dating of medieval fireplaces at the Muhlegasse, Zurich, in Journal of Archaeological Science, 39(7), 2153-2166.
Reconstructing the Holocene Geomagnetic Field
Korte M, Constable C, Donadini F, Holme R (2011), Reconstructing the Holocene Geomagnetic Field, in Earth and Planetary Science Letters, 312, 497-505.
Variational data assimilation for the initial value dynamo problem
Li K (2011), Variational data assimilation for the initial value dynamo problem, in Physical Review E, 84, 056321-1-056321-16.
Archeomagnetic study of Roman lime kilns (1c. AD) and one pottery kiln (1c. BC - 1c. AD) at Krivina, Bulgaria, as a contribution to archeomagnetic dating
Donadini F, Kovacheva M, Kostadinova-Avramova M (2010), Archeomagnetic study of Roman lime kilns (1c. AD) and one pottery kiln (1c. BC - 1c. AD) at Krivina, Bulgaria, as a contribution to archeomagnetic dating, in Archaeologia Bulgarica, 14(2), 23-37.

Collaboration

Group / person Country
Types of collaboration
University of Leeds Great Britain and Northern Ireland (Europe)
- Publication

Associated projects

Number Title Start Funding scheme
112293 Development and analysis of models of magnetic field generation in the Earth's core 01.06.2007 Project funding
143596 The geomagnetic field over multiple time scales: Measurements, models, and mechanisms 01.10.2012 Project funding

Abstract

We describe research aimed at elucidating the evolution of the magnetic field over the last 8000 years, focusing on short timescales (such as the last few decades, during which there is excellent data quality), medium timescales of hundreds of years (where actual magnetic field measurements are available), and long timescales (where archaeomagneticdata can be used). Our aim is to focus for the first time on 3-dimensional models of the magnetic field in the interior of the core, and to adopt a variational data assimilation technique to optimally fit the available data whilst honouring the relevant physics. In order to find the best possible models for the archaeomagnetic evolution of the field we describe data collection activities aimed at improving the database that is used to constrain the model.A minimal-physics dynamical evolution model for the Earth’s core is used in conjunction with observations to find the initial conditions that lead to an evolution of the system best in accord with the observations. In order todiscover this model we adopt a variational data assimilation technique, employing an adjoint model, to optimally solve the problem. Central to our creation of a time-varying model for the last 8000 years is the collection of new archaeomagnetic data to improve the temporal constraints available in Europe. Sites in Itay, Switzerland and Bulgaria present constraints over the period range 6000BC to 1100AD, which will be used in conjunction with the existing GEOMAGIA database of archaeomagnetic measurements. In addition we propose a major study of previouslyanalysed archaeomagnetic data from the United States. These data are in the form of demagnetisation curves, but require some effort to determine archaeo declinations, inclinations and ages.An important part of the project are two allied PhD studentships that will develop the mathematical tools required for the project. The key results that will be of interest are an elucidation of the interior magnetic field structure in the Earth’s core, including for the first time a constraint on the toroidal component of the field, normally hidden from view. The strength of these interior fields is of interest for many reasons, not least their importance in the energy budget of the core. This has implications ultimately for the heat transferred from the core to the mantle, and the ageof the inner core, still poorly known.We also expect to determine buoyancy (i.e. temperature) in the core that contributes to the time-evolution of the convection (this forms one PhD project). On short timescales we plan to examine the applicability of a Hamiltonian formulation of the fluid dynamics in which certain physical quantities, such as energy and vorticity, are conserved.The outputs from the project will be (a) new models for magnetic field evolution over (i) 6000BC-2000AD (ii) 1590-2010 (iii) 1960-2010 that will be freely distributed to the community (b) New constraints on field evolution over Europe and America for the last few thousand years as a result of new data. (c) Probable calibration of relative palaeointensity curves being currently acquired by Prof. A. Hirt from Swiss lake cores (ETH CHIRP project) (d) An enhanced understanding of magnetic field structure within the core, along with the complementary buoyancy distribution.
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