Skip to main content Accessibility help
×
Hostname: page-component-78c5997874-8bhkd Total loading time: 0 Render date: 2024-11-06T02:26:59.524Z Has data issue: false hasContentIssue false

Testing for Dynamo Action

Published online by Cambridge University Press:  11 May 2010

D.W. Hughes
Affiliation:
Department of Applied Mathematical Studies, The University, Leeds, LS2 9JT UK
M. R. E. Proctor
Affiliation:
University of Cambridge
P. C. Matthews
Affiliation:
University of Cambridge
A. M. Rucklidge
Affiliation:
University of Cambridge
Get access

Summary

It is important to determine whether a cosmical magnetic field is a consequence of dynamo action or, alternatively, is a slowly decaying fossil field. Similarly, in numerical simulations of magnetohydrodynamic turbulence we should like to distinguish between a dynamo-generated magnetic field and one that is simply decaying, albeit slowly. Here certain criteria are presented that must be satisfied before any positive claims can be made for dynamo action.

INTRODUCTION

Given the existence of a naturally occurring magnetic field, be it astrophysical or geophysical, it is natural to ask whether the field is generated by dynamo action or if instead it is a fossil field, trapped in the body since its formation. In certain contexts it is possible to give a definitive answer. For example, the Ohmic diffusion time of the Earth's core is of the order of 10 years whereas paleomagnetic records show that the magnetic field of the Earth has existed for 109 years. Consequently, since the field has been maintained for so many Ohmic decay times it must be generated by some sort of dynamo process. For astrophysical bodies on the other hand, for which typically the Ohmic time is comparable to the lifetime of the body itself, it is not so straightforward to assert that a field is dynamo-generated. Of course, there may be other factors suggesting the origin of the field, but simply on the basis of the Ohmic decay time the issue often cannot be decided. What we would like therefore is a test to distinguish between these two possibilities.

Type
Chapter
Information
Publisher: Cambridge University Press
Print publication year: 1994

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

Save book to Kindle

To save this book to your Kindle, first ensure [email protected] is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.

Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.

Find out more about the Kindle Personal Document Service.

Available formats
×

Save book to Dropbox

To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Dropbox.

Available formats
×

Save book to Google Drive

To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.

Available formats
×