Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm11b1749m&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SM11B-1749
Physics
[2752] Magnetospheric Physics / Mhd Waves And Instabilities, [2753] Magnetospheric Physics / Numerical Modeling
Scientific paper
We consider a linearization of the multi-fluid magnetohydrodynamic equations underlying the Multi-Fluid Lyon-Fedder-Mobarry (MFLFM) global magnetosphere model. The model is based on two simplifying assumptions that are common to treatments of single-ion fluid plasmas: a Maxwellian distribution function in the frame moving with the speed of the electrical drift, ěc v{E}=ěc E × ěc B, and a macroscopic plasma velocity in the direction perpendicular to the magnetic field that coincides with the electrical drift velocity and therefore is the same for all ion species, ěc vα ,⊥=ěc v⊥=ěc v{E}. We derive a set of linearized equations describing the basic MHD modes in a two-ion species system governed by the multi-fluid MHD equations. We show that in addition to the Alfv{´ e}n, fast and slow waves found in single-species MHD plasmas, there appears an additional mode that possesses qualities of both fast and slow waves, and operates by transmitting thermal energy perturbations from one fluid to the other through interaction with the magnetic field. This wave, as well as the Alfv{´ e}n, fast and slow waves, is shown to be always stable in the situation when the two-fluids have no field-aligned streaming velocity, i.e. their field-aligned velocities are the same. We will discuss the similarities and differences in the behavior of this additional wave with the fast and slow modes in the low and high Mach-number limits. Regardless of the Mach number, the additional wave is similar to the slow mode in that it does not propagate in the direction perpendicular to the background magnetic field as opposed to the fast wave which is roughly isotropic. Our results may be important for understanding of some phenomena occurring in multi-fluid MHD plasmas governed by our initial set of equations. Some possible applications include the development of the Kelvin-Helmholtz instability at the magnetopause, and whether it should follow predictions based on the single-fluid MHD theory, and the reconnection on the magnetopause where, even single-species hydrogen plasma exhibits multi-streaming, and the streaming velocity can be as large or larger than the thermal speeds of the two populations.
Lyon John
Merkin V. G.
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