Physics – Plasma Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsm13a1647w&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #SM13A-1647
Physics
Plasma Physics
2704 Auroral Phenomena (2407), 2716 Energetic Particles: Precipitating, 2753 Numerical Modeling, 7829 Kinetic Waves And Instabilities, 7867 Wave/Particle Interactions (2483, 6984)
Scientific paper
Observational evidence is accumulating which demonstrates the importance of shear Alfvén waves (SAW) for auroral electron acceleration, especially in active regions of the magnetosphere, such as near the cusp and at auroral latitudes in the midnight sector. It has been shown - through theory, numerical experiment and laboratory experiment - that SAW with short perpendicular scale lengths carry parallel electric fields which may explain the resulting auroral electron acceleration in the Earth's magnetosphere. However, many details regarding the interaction of SAW with electrons are still not well understood, despite decades of research. The location of electron acceleration due to SAW in the magnetosphere is unclear, and we have yet to fully reconcile the range of electron energies possible through this acceleration process with the energy ranges required to deliver the observed auroral displays. As shear Alfvén waves travel from the magnetosphere towards the ionosphere, they leave regions of sparse, hot plasma and travel towards the ionosphere, where the plasma becomes denser and colder. The waves also experience an increase in magnetic field strength as they approach the ionosphere. These gradients in the plasma environment result in changes in the characteristics of the SAW, especially in the sign and strength of the accompanying parallel electric field. We present results from a self-consistent kinetic simulation code (DK1D: Watt and Rankin, Plasma Physics and Controlled Fusion, 50, 074008, [2008]) to demonstrate how the characteristics of the wave, and the resulting wave-particle interactions, change as SAW propagate through an inhomogeneous plasma. We compare the results with those predicted from local two-fluid theory, and show which locations along an auroral field line may be most conducive to auroral electron acceleration by SAW.
Rankin Robert
Watt C. E.
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