Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsm52a..05l&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #SM52A-05
Physics
2704 Auroral Phenomena (2407), 2721 Field-Aligned Currents And Current Systems (2409), 2736 Magnetosphere/Ionosphere Interactions (2431), 2790 Substorms, 7845 Particle Acceleration
Scientific paper
Observations of auroral particles indicate that in many cases the auroral energy distribution is broad in energy and strongly field-aligned in pitch angle. These observations have been interpreted in terms of time dependent acceleration of electrons in fluctuating electric fields associated with kinetic Alfvén waves trapped in the ionospheric Alfvén resonator, leading them to be termed "Alfvénic aurora." Observations from FAST and IMAGE indicate that the auroral arc that brightens during substorm onset is predominantly Alfvénic, suggesting that it is a transitional phase to the quasi-static aurora. This interpretation is also supported by measurements from THEMIS, which have found cases in which the auroral arc brightens before the establishment of a quasi-static substorm current wedge. These waves may also be associated with Pi1 pulsations observed at substorm onset; however, the waves observed on the ground must have large perpendicular wavelength while the kinetic Alfvén waves that can accelerate electrons have small wavelength, indicating that a transfer of energy across scales must take place. The implication of these theoretical considerations for the physics of current generation and the timing of substorm processes will be discussed.
Lysak Robert L.
Song Yushu
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