Interchange Instability in a Plasma Connected to a Conducting Ionosphere

Details Interchange Instability in a Plasma Connected to a Conducting Ionosphere Interchange Instability in a Plasma Connected to a Conducting Ionosphere

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsm33b0367x&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #SM33B-0367

Other

2721 Field-Aligned Currents And Current Systems (2409), 2730 Magnetosphere: Inner, 2736 Magnetosphere/Ionosphere Interactions (2431), 2752 Mhd Waves And Instabilities (2149, 6050, 7836), 2764 Plasma Sheet

Scientific paper

We have combined the Tsyganenko and Stern [1996] magnetic field model and the Tsyganenko and Mukai [2003] plasma sheet statistical model to estimate the entropy parameter PV^{γ}, where P is the plasma sheet pressure and V=\int ds/B is the flux tube volume containing one unit of magnetic flux. The contour plots for PV^{γ} and V in the equatorial plane suggest that, although both PV^{γ} and V generally increase tailward, their gradients are generally not parallel or antiparallel to each other, whereas most theoretical discussions of interchange instability assume that these two vectors are lined up. We present some first analytical calculations to investigate the criterion for interchange instability in a quasi-static, low β plasma that is connected to a conducting ionosphere and has ∇ PV^{γ} and ∇ V at an arbitrary angle α. A boundary layer is assumed to separate two regions with different but uniform PV^{γ}. The main conclusion is that the system is interchange unstable if α>π/2. The growth rate is approximately proportional to -cos(α) if the ripple wavelength is long compare to the boundary layer thickness. The results suggest that the usual plasma sheet configuration is interchange stable, since the statistical plasma sheet models indicate that α<π/2. Our conclusion differs from an earlier analysis of a similar problem by Volkov and Mal'tsev [1986], who ignored the effects of shear-velocity terms, which must be present in situations where ∇ PV^{γ} and ∇ Vare neither parallel nor anti-parallel.

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