On the MHD boundary of Kelvin-Helmholtz stability diagram at large wavelengths

Mostrar todas las versiones(3)

Working within the domain of inviscid incompressible MHD theory, we found that a tangential discontinuity (TD) separating two uniform regions of different density, velocity and magnetic field may be Kelvin-Helmholtz (KH) stable and yet a study of a transition between the same constant regions given...

Descripción completa

Guardado en:
Detalles Bibliográficos
Autores principales: Gratton, F.T., Gnavi, G., Farrugia, C.J., Bender, L.
Formato: Artículo publishedVersion
Publicado: 2004
Acceso en línea:http://hdl.handle.net/20.500.12110/paper_01039733_v34_n4B_p1804_Gratton
https://repositoriouba.sisbi.uba.ar/gsdl/cgi-bin/library.cgi?a=d&c=artiaex&d=paper_01039733_v34_n4B_p1804_Gratton_oai
Aporte de:
Repositorio Digital de la Universidad de Buenos Aires (UBA) de Universidad de Buenos Aires
id I28-R145-paper_01039733_v34_n4B_p1804_Gratton_oai
record_format dspace
spelling I28-R145-paper_01039733_v34_n4B_p1804_Gratton_oai2024-08-16 Gratton, F.T. Gnavi, G. Farrugia, C.J. Bender, L. 2004 Working within the domain of inviscid incompressible MHD theory, we found that a tangential discontinuity (TD) separating two uniform regions of different density, velocity and magnetic field may be Kelvin-Helmholtz (KH) stable and yet a study of a transition between the same constant regions given by a continuous velocity profile shows the presence of the instability with significant growth rates. Since the cause of the instability stems from the velocity gradient, and since a TD may be considered as the ultimate limit of such gradient, the statement comes as a surprise. In fact, a long wavelength (λ) boundary for the KH instability does not exist in ordinary liquids being instead a consequence of the presence of magnetic shear, a possibility that has passed unnoticed in the literature. It is shown that KH modes of a magnetic field configuration with constant direction do not have the long A boundary. A theoretical explanation of this feature and examples of the violation of the TD stability condition are given using a model that can be solved in closed form. Stability diagrams in the (kd, MA) plane are given (where kd = 2πd/λ, 2d is the velocity gradient length scale, and MA is the Alfvénic Mach number) that show both the well-known limit at small λs and the boundary for large but finite As noted here. Consequences of this issue are relevant for stability studies of the dayside magnetopause as the stability condition for a TD should be used with care in data analysis work. Fil:Gratton, F.T. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Fil:Gnavi, G. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Fil:Bender, L. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. application/pdf http://hdl.handle.net/20.500.12110/paper_01039733_v34_n4B_p1804_Gratton info:eu-repo/semantics/openAccess http://creativecommons.org/licenses/by/2.5/ar Braz. J. Phys. 2004;34(4 B):1804-1813 On the MHD boundary of Kelvin-Helmholtz stability diagram at large wavelengths info:eu-repo/semantics/article info:ar-repo/semantics/artículo info:eu-repo/semantics/publishedVersion https://repositoriouba.sisbi.uba.ar/gsdl/cgi-bin/library.cgi?a=d&c=artiaex&d=paper_01039733_v34_n4B_p1804_Gratton_oai
institution Universidad de Buenos Aires
institution_str I-28
repository_str R-145
collection Repositorio Digital de la Universidad de Buenos Aires (UBA)
description Working within the domain of inviscid incompressible MHD theory, we found that a tangential discontinuity (TD) separating two uniform regions of different density, velocity and magnetic field may be Kelvin-Helmholtz (KH) stable and yet a study of a transition between the same constant regions given by a continuous velocity profile shows the presence of the instability with significant growth rates. Since the cause of the instability stems from the velocity gradient, and since a TD may be considered as the ultimate limit of such gradient, the statement comes as a surprise. In fact, a long wavelength (λ) boundary for the KH instability does not exist in ordinary liquids being instead a consequence of the presence of magnetic shear, a possibility that has passed unnoticed in the literature. It is shown that KH modes of a magnetic field configuration with constant direction do not have the long A boundary. A theoretical explanation of this feature and examples of the violation of the TD stability condition are given using a model that can be solved in closed form. Stability diagrams in the (kd, MA) plane are given (where kd = 2πd/λ, 2d is the velocity gradient length scale, and MA is the Alfvénic Mach number) that show both the well-known limit at small λs and the boundary for large but finite As noted here. Consequences of this issue are relevant for stability studies of the dayside magnetopause as the stability condition for a TD should be used with care in data analysis work.
format Artículo
Artículo
publishedVersion
author Gratton, F.T.
Gnavi, G.
Farrugia, C.J.
Bender, L.
spellingShingle Gratton, F.T.
Gnavi, G.
Farrugia, C.J.
Bender, L.
On the MHD boundary of Kelvin-Helmholtz stability diagram at large wavelengths
author_facet Gratton, F.T.
Gnavi, G.
Farrugia, C.J.
Bender, L.
author_sort Gratton, F.T.
title On the MHD boundary of Kelvin-Helmholtz stability diagram at large wavelengths
title_short On the MHD boundary of Kelvin-Helmholtz stability diagram at large wavelengths
title_full On the MHD boundary of Kelvin-Helmholtz stability diagram at large wavelengths
title_fullStr On the MHD boundary of Kelvin-Helmholtz stability diagram at large wavelengths
title_full_unstemmed On the MHD boundary of Kelvin-Helmholtz stability diagram at large wavelengths
title_sort on the mhd boundary of kelvin-helmholtz stability diagram at large wavelengths
publishDate 2004
url http://hdl.handle.net/20.500.12110/paper_01039733_v34_n4B_p1804_Gratton
https://repositoriouba.sisbi.uba.ar/gsdl/cgi-bin/library.cgi?a=d&c=artiaex&d=paper_01039733_v34_n4B_p1804_Gratton_oai
work_keys_str_mv AT grattonft onthemhdboundaryofkelvinhelmholtzstabilitydiagramatlargewavelengths
AT gnavig onthemhdboundaryofkelvinhelmholtzstabilitydiagramatlargewavelengths
AT farrugiacj onthemhdboundaryofkelvinhelmholtzstabilitydiagramatlargewavelengths
AT benderl onthemhdboundaryofkelvinhelmholtzstabilitydiagramatlargewavelengths
_version_ 1809357088329039872

Ejemplares similares