Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm52a..03w&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SM52A-03
Physics
[2752] Magnetospheric Physics / Mhd Waves And Instabilities, [2764] Magnetospheric Physics / Plasma Sheet, [2790] Magnetospheric Physics / Substorms
Scientific paper
We consider ideal-MHD oscillations in a hot plasma on closed field lines that thread through finite-conductance boundaries. An equilibrium in such a system is stable against interchange instability if the gradient of the entropy parameter PV5/3 is everywhere parallel to the gradient of log(V) minus b/2 times the gradient of log(P), where P is pressure, V is the volume of a flux tube with one unit of magnetic flux, and b is the flux tube average of plasma beta. If a stable system at rest is disturbed slightly, it will either decay back to its stable configuration or execute a decaying oscillation, which we call an "interchange oscillation". We consider the special case where the initial disturbance takes the form of a bubble, specifically the reduction of PV5/3 on a thin filament. Results are presented for cases that resemble the plasma sheet with field lines connecting to the conducting ionosphere. The simulations indicate that a filament that is confined to the low-beta region near the Earth exhibits simple damping, while a filament that extends well out into the plasma sheet executes a damped oscillation. The period of the oscillation depends on the gradient of PV5/3 and is usually longer than the period of a slow mode wave traveling along the filament. We suggest that the Pi2 oscillations that accompany substorm expansions and bursty bulk flows are interchange oscillations.
Chen Chian-Chou
Toffoletto Frank
Wolf Richard A.
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