Compositional convection in the presence of a magnetic field. I. A single interface

I. A. Eltayeb, E. A. Hamza, J. A. Jervase, E. Krishnan, D. E. Loper

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

We investigate the stability of a vertical interface separating two semi-infinite fluids with differing composition of light material and permeated by a magnetic field. Both fluids possess finite kinematic viscosity, ν, thermal diffusivity, κ, magnetic diffusivity, η, and negligible material diffusion. The stability depends on six dimensionless parameters: the Prandtl number, σ (where σ = ν/κ), the magnetic Prandtl number, σm = ν/η, the Chandrasekhar number, Q c, the Reynolds number, Re, and the ratios, Bv, Γ of the vertical and normal components to the lateral component of field. A comprehensive study of the dependence of the stability on the parameters is made when Re is small. The presence of a horizontal magnetic field tends to reduce the growth rate of the non-magnetic modes and can also give rise to new modes of instability. The addition of a vertical component of field can completely counteract the stabilizing influence of the horizontal component. For field strengths in excess of some value dependent on σ, σm and Bv, the non-magnetic unstable mode is replaced by one of two magnetic modes, one of which is a roll aligned with the field and the other inclined to it. The helicity and α-effect of the small-scale unstable motions are also discussed.

Original languageEnglish
Pages (from-to)3505-3528
Number of pages24
JournalProceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences
Volume460
Issue number2052
DOIs
Publication statusPublished - Dec 8 2004

Fingerprint

Convection
convection
Magnetic Field
Magnetic fields
Vertical
Prandtl number
magnetic fields
Horizontal
Unstable
Thermal Diffusivity
Fluid
Fluids
Helicity
fluids
Thermal diffusivity
Inclined
thermal diffusivity
Diffusivity
Dimensionless
diffusivity

Keywords

  • α-effect
  • Compositional convection
  • Compositional plumes
  • Geodynamo
  • Helicity
  • Hydromagnetic stability

ASJC Scopus subject areas

  • General

Cite this

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abstract = "We investigate the stability of a vertical interface separating two semi-infinite fluids with differing composition of light material and permeated by a magnetic field. Both fluids possess finite kinematic viscosity, ν, thermal diffusivity, κ, magnetic diffusivity, η, and negligible material diffusion. The stability depends on six dimensionless parameters: the Prandtl number, σ (where σ = ν/κ), the magnetic Prandtl number, σm = ν/η, the Chandrasekhar number, Q c, the Reynolds number, Re, and the ratios, Bv, Γ of the vertical and normal components to the lateral component of field. A comprehensive study of the dependence of the stability on the parameters is made when Re is small. The presence of a horizontal magnetic field tends to reduce the growth rate of the non-magnetic modes and can also give rise to new modes of instability. The addition of a vertical component of field can completely counteract the stabilizing influence of the horizontal component. For field strengths in excess of some value dependent on σ, σm and Bv, the non-magnetic unstable mode is replaced by one of two magnetic modes, one of which is a roll aligned with the field and the other inclined to it. The helicity and α-effect of the small-scale unstable motions are also discussed.",
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T1 - Compositional convection in the presence of a magnetic field. I. A single interface

AU - Eltayeb, I. A.

AU - Hamza, E. A.

AU - Jervase, J. A.

AU - Krishnan, E.

AU - Loper, D. E.

PY - 2004/12/8

Y1 - 2004/12/8

N2 - We investigate the stability of a vertical interface separating two semi-infinite fluids with differing composition of light material and permeated by a magnetic field. Both fluids possess finite kinematic viscosity, ν, thermal diffusivity, κ, magnetic diffusivity, η, and negligible material diffusion. The stability depends on six dimensionless parameters: the Prandtl number, σ (where σ = ν/κ), the magnetic Prandtl number, σm = ν/η, the Chandrasekhar number, Q c, the Reynolds number, Re, and the ratios, Bv, Γ of the vertical and normal components to the lateral component of field. A comprehensive study of the dependence of the stability on the parameters is made when Re is small. The presence of a horizontal magnetic field tends to reduce the growth rate of the non-magnetic modes and can also give rise to new modes of instability. The addition of a vertical component of field can completely counteract the stabilizing influence of the horizontal component. For field strengths in excess of some value dependent on σ, σm and Bv, the non-magnetic unstable mode is replaced by one of two magnetic modes, one of which is a roll aligned with the field and the other inclined to it. The helicity and α-effect of the small-scale unstable motions are also discussed.

AB - We investigate the stability of a vertical interface separating two semi-infinite fluids with differing composition of light material and permeated by a magnetic field. Both fluids possess finite kinematic viscosity, ν, thermal diffusivity, κ, magnetic diffusivity, η, and negligible material diffusion. The stability depends on six dimensionless parameters: the Prandtl number, σ (where σ = ν/κ), the magnetic Prandtl number, σm = ν/η, the Chandrasekhar number, Q c, the Reynolds number, Re, and the ratios, Bv, Γ of the vertical and normal components to the lateral component of field. A comprehensive study of the dependence of the stability on the parameters is made when Re is small. The presence of a horizontal magnetic field tends to reduce the growth rate of the non-magnetic modes and can also give rise to new modes of instability. The addition of a vertical component of field can completely counteract the stabilizing influence of the horizontal component. For field strengths in excess of some value dependent on σ, σm and Bv, the non-magnetic unstable mode is replaced by one of two magnetic modes, one of which is a roll aligned with the field and the other inclined to it. The helicity and α-effect of the small-scale unstable motions are also discussed.

KW - α-effect

KW - Compositional convection

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KW - Geodynamo

KW - Helicity

KW - Hydromagnetic stability

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