Alfvén Wave Generation and Dissipation Leading to High-Latitude Aurora

Physics

Scientific paper

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2427 Ionosphere/Atmosphere Interactions (0335), 2704 Auroral Phenomena (2407), 2736 Magnetosphere/Ionosphere Interactions, 2752 Mhd Waves And Instabilities, 2764 Plasma Sheet

Scientific paper

An overview is given of theory and models that describe the generation of magnetically guided Alfvén waves in the magnetotail, their propagation in the boundary plasma sheet, fate in the low-altitude magnetosphere and ionosphere, and effectiveness in powering high-latitude aurora. Possible sources of Alfvénic fluctuations observed in the boundary plasma sheet region include i) time-variable reconnection and ii) mode conversion of compressional and surface waves in the plasma sheet boundary layer. The Alfvén waves are only weakly attenuated at high altitude as they travel earthward unless they are generated with ion gyroscale structure. The Alfvén wave field-aligned current and electric field intensify at low-altitude due to flux tube convergence, introducing nonlinear effects. Possible outcomes include: (1) Small-scale inertial Alfvén waves capable of accelerating electrons along the ambient field are manufactured by large-transverse-scale Alfvén waves interacting with an active ionosphere; (2) Parallel electric fields and field-aligned electron beams form near 1 RE where large electron parallel velocities are needed to sustain the wave field-aligned current; and (3) Some fraction of the Alfvén wave power is reflected by the ionosphere and collisionless dissipation layers in (2). The Alfvén wave absorption and effectiveness in producing aurora depend on both the transverse wavenumber spectrum and wave amplitude at low altitude.

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