Dušan Jovanović
Fluid Theory of Coherent Magnetic structures in Space PlasmasAbstract
In situ observations in Earth’s and Saturn’s magnetosheaths and in the
solar wind reveal the Alfvén vortices as intermittent structures whose
scales range from fluid lengths down to a few ion lengths. We develop a
new model of magnetic vortices in high-beta plasmas, possessing
compressible density and magnetic field, whose typical size goes from
fluid to ion scales. At magnetofluid scales, we find 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 localized inside the vortex core. At ion or kinetic scales
(with the smallest radii and in the absence of acoustic perturbations,
only dipolar Alfvén vortices survive with properties similar to those at
fluid scales, except that $\frac{\delta n}{n_0}$ reaches the level of $\frac{dB}{B_0}$.We also find
pressure-balanced kinetic slow magnetosonic dipoles, possessing finite
parallel electric field and purely compressional magnetic field
perturbation, whose existence is facilitated by a strong ion temperature
anisotropy.
|