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Article Dans Une Revue The Astrophysical Journal Année : 2020

Fluid Theory of Coherent Magnetic Vortices in High- β Space Plasmas

Résumé

In situ observations in Earth's and Saturn's magnetosheaths and in the solar wind reveal the presence of Alfvén vortices as intermittent structures in the range of scales from fluid lengths down to a few ion lengths. The density and the magnetic field associated with them appear to be compressible for higher plasma betas. Until now, only incompressible Alfvén vortices have been known. Motivated by space plasma observations, we develop a new model of magnetic vortices in high-beta plasmas with anisotropic temperature, possessing compressible density and magnetic field, whose typical size ranges from fluid to ion scales. At magnetofluid scales, we find novel nonpropagating field-aligned cylindrical monopoles and inclined propagating dipoles. Their transverse magnetic and velocity fluctuations are aligned, but not identical, and they exhibit density and compressible magnetic field fluctuations δn and δB∥ localized inside the vortex core. In the presence of thermal anisotropy and acoustic effects, they may be correlated or anticorrelated, δn/δB∥=constant≷0; fluctuations whose velocity along the magnetic field is below the ion thermal speed are always correlated. At ion or kinetic scales (with the smallest radii ∼c/ωpi,ρLi ) and in the absence of acoustic perturbations, only dipolar Alfvén vortices survive with properties similar to those at fluid scales, except that δn/n0 reaches the level of δB∥/B0 . We also find pressure-balanced kinetic slow magnetosonic dipoles, possessing finite E∥ and purely compressional magnetic field perturbation, whose existence is facilitated by a strong ion temperature anisotropy.

Dates et versions

hal-03254782 , version 1 (09-06-2021)

Identifiants

Citer

Dušan Jovanović, Olga Alexandrova, Milan Maksimović, Milivoj Belić. Fluid Theory of Coherent Magnetic Vortices in High- β Space Plasmas. The Astrophysical Journal, 2020, 896 (1), pp.8. ⟨10.3847/1538-4357/ab8a45⟩. ⟨hal-03254782⟩
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