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A coupled low order dynamo/turbulent shell model for geomagnetic field variations and reversals

Lookup NU author(s): David Ryan, Dr Graeme Sarson

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Abstract

We couple a low order alpha omega dynamo model to a shell model of turbulence, with the dynamo a-effect being identified with the helicity of the shell model. Fluctuations ('noise') in this term lead to lognormal-like statistics in the magnetic field, as was noted for inter-reversal duration by Ryan and Sarson (2007). Here we extend the analysis to shorter time-scale field variations (viz. Virtual Axial Dipole Moments, VADMs), and find that a lognormal distribution is also a significant fit for this quantity, both for the output from our model and for the observed paleomagnetic data. This shared lognormality - which Ryan and Sarson (2007) argued arose from a common source in terms of 'multiplicative noise' in the underlying dynamo mechanism - makes the synthetic and observed data comparable; we also note some similarities in the patterns of VADM fluctuations (including asymmetric decay and recovery, epitomised in an extreme form by the controversial 'saw-tooth' pattern) and in reversal inter-event times (chrons) of widely varying duration. We describe the dynamics behind our coupled model, and discuss the effect of certain model parameters on the synthetic chron durations, including the occurrence of superchrons. Implications for the observed geomagnetic field behaviour are discussed. (C) 2011 Elsevier B.V. All rights reserved.


Publication metadata

Author(s): Ryan DA, Sarson GR

Publication type: Article

Publication status: Published

Journal: Physics of the Earth and Planetary Interiors

Year: 2011

Volume: 188

Issue: 3-4

Pages: 214-234

Print publication date: 21/09/2011

ISSN (print): 0031-9201

ISSN (electronic): 1872-7395

Publisher: Elsevier BV

URL: http://dx.doi.org/10.1016/j.pepi.2011.09.003

DOI: 10.1016/j.pepi.2011.09.003

Notes: Proceedings of the 12th Symposium of Study of the Earth's Deep Interior (SEDI)


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