On the role of strain rate and vorticity in plasmas

Polygiannakis, JM; Moussas, X

dc.contributor.author	Polygiannakis, JM	en
dc.contributor.author	Moussas, X	en
dc.date.accessioned	2014-03-01T01:48:59Z
dc.date.available	2014-03-01T01:48:59Z
dc.date.issued	1999	en
dc.identifier.issn	0741-3335	en
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/25641
dc.subject.classification	Physics, Fluids & Plasmas	en
dc.subject.classification	Physics, Nuclear	en
dc.subject.other	SOLAR-WIND FLUCTUATIONS	en
dc.subject.other	MHD VORTEX STREET	en
dc.subject.other	MAGNETIC-FIELD	en
dc.subject.other	INTERSTELLAR TURBULENCE	en
dc.subject.other	ALFVENIC FLUCTUATIONS	en
dc.subject.other	OUTER HELIOSPHERE	en
dc.subject.other	MINIMUM-VARIANCE	en
dc.subject.other	VISCOSITY	en
dc.subject.other	MODEL	en
dc.subject.other	ANISOTROPY	en
dc.title	On the role of strain rate and vorticity in plasmas	en
heal.type	journalArticle	en
heal.language	English	en
heal.publicationDate	1999	en
heal.abstract	It is shown that the magnetic field's local evolution in plasmas is directly affected by an interplay between the deformation (strain rate) and the self-rotation (vorticity) of the elementary plasma fluid volumes. At regions of strong strain rate, the fast local convergence or divergence of the flow causes exponential increase or decrease of the field's components, respectively. At regions of strong vorticity, faster directional than magnitude variations of the field occur, explaining the field alignment of the field minimum-variance direction and the random wandering of the field's tip on a sphere, both observed in the solar wind plasma, even in the absence of Alfven waves. We further investigate the coupling between the maximum strain-rate direction and the local magnetic field, that was previously deduced from magnetic field measurements in the outer heliosphere. Cases of long-lasting, non-Parkerian, radial heliospheric magnetic field are also shown to be periods of field-aligned strain rate. A statistical proof for this alignment is given, assuming that the small-scale field fluctuations are weakly stationary and time reversible. We further propose a generalization of the Stokesian fluid stress-strain relation to the case of one-fluid collisionless MHD plasmas, including the effects of turbulent viscosity acid magnetically induced shearing motion. For a negligible or isotropic or 'field-aligned' thermal pressure tensor, the proposed 'Stokesian plasma' relation implies the field alignment of the solar wind plasma strain-rate direction and leads to anisotropic stress-strain balance equations, related to those of 'firehose' plasma instability. The field alignment of a principal strain-rate direction leads to simplifications in the magnetic-induction equation, especially in the case of force-free fields. For the simplified case of homogeneous isotropic and incompressible plasma turbulence, the proposed stress-strain-rate relation implies that the velocity and magnetic field inertial range spectra should be identical, further reducing to the Kolmogorov-like k(-5/3) law for scale-invariant eddy cascade at constant energy-dissipation rate.	en
heal.publisher	IOP PUBLISHING LTD	en
heal.journalName	PLASMA PHYSICS AND CONTROLLED FUSION	en
dc.identifier.isi	ISI:000082486100004	en
dc.identifier.volume	41	en
dc.identifier.issue	8	en
dc.identifier.spage	967	en
dc.identifier.epage	983	en