Physics
Scientific paper
May 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agusmsm22a..05m&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #SM22A-05
Physics
2704 Auroral Phenomena (2407), 2748 Magnetotail Boundary Layers, 2764 Plasma Sheet, 2790 Substorms
Scientific paper
A survey of substorm observations with IMAGE FUV and FAST satellite in situ data provided many cases in which the onset events occurred in the proximity of the FAST particle and field measurements. The IMAGE FUV experiment took a 10 second duration exposure every two minutes and the substorm onset was determined with this timing accuracy. The time when FAST observed the largest electron fluxes was used to determine the observation time phase related to onset. In the FAST satellite data, Alfven wave produced aurora can be recognized by the dominance of intense fluxes of magnetic field-aligned electrons having a broad, structured energy spectrum and accompanying intense wave activity. These events can be distinguished from "inverted V" auroras produced by quasi-static field aligned electric fields from their characteristic mono- energetic spectral signature. The Alfven wave accelerated electron auroras are produced by converting high intensity wave energy (Poynting) fluxes into electron energy and therefore these auroras can be regarded as the footprints of regions where large amplitude Alfven waves are produced by magnetic reconfigurations. During the substorm expansion phase Alfven wave accelerated electrons occur at the poleward boundary of the expanding substorm surge, while equatorward of the surge there is a broader region of electron precipitation with embedded strong quasi-static "inverted V" electric fields. This is consistent with wave signatures of dipolarization and the motion of a magnetospheric boundary. Ion conics and intense ion outflow is often seen in the region of Alfvenic auroras. Nearer to the onset time, Alfvenic aurora is seen deep within the auroral oval near the point of the initial brightening. This is consistent with prior observations that the most equatorward arc breaks up first at substorm onset. In all cases the Alfven wave accelerated auroras, unlike inverted V-s, do not appear to carry strong net field aligned return currents from the ionosphere into the magnetosphere.
Carlson Carl
Frey Harald
Mende Stephen
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