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Potential vorticity in magnetohydrodynamics

Published online by Cambridge University Press:  05 September 2014

G. M. Webb*
Affiliation:
Center for Space Plasma and Aeronomic Research, The University of Alabama in Huntsville, Huntsville AL 35805, USA
R. L. Mace
Affiliation:
School of Chemistry and Physics, The University of KwaZulu-Natal, Durban Westville, Durban, Natal 4000, South Africa
*
Email address for correspondence: gmw0002@uah.edu

Abstract

A version of Noether's second theorem using Lagrange multipliers is used to investigate fluid relabelling symmetries conservation laws in magnetohydrodynamics (MHD). We obtain a new generalized potential vorticity type conservation equation for MHD which takes into account entropy gradients and the J × B force on the plasma due to the current J and magnetic induction B. This new conservation law for MHD is derived by using Noether's second theorem in conjunction with a class of fluid relabelling symmetries in which the symmetry generator for the Lagrange label transformations is non-parallel to the magnetic field induction in Lagrange label space. This is associated with an Abelian Lie pseudo algebra and a foliated phase space in Lagrange label space. It contains as a special case Ertel's theorem in ideal fluid mechanics. An independent derivation shows that the new conservation law is also valid for more general physical situations.

Type
Research Article
Copyright
Copyright © Cambridge University Press 2014 

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