Paper#: 97
Poster #: 25
Session Name: Poster Session 1
Room: East Ballroom
Day: Tuesday
Time: 10:10 a.m.-Noon
Abstract Title: Growth-Phase Auroral Arcs
PresentSurname: Lessard, M.
All Authors: M. Lessard, W. Lotko, W. Peria, C.W. Carlson, F. Creutzberg
Abstract : During a substorm growth phase, auroral arcs observed on the ground are known to migrate equatorward. This motion is thought to be associated with a stretching of the nightside magnetotail as a result of an enhanced transfer of solar wind energy to the magnetosphere. Following slow growth, substorm onset is then observed as a brightening of this arc. The importance of this pre-existing arc is difficult to exaggerate, since its presence is evidence for a region with enhanced coupling between the magnetosphere and ionosphere that exists before onset. Recent analysis of data from FAST and CANOPUS has shown that these arcs can persist as stationary arcs or, at times, can exhibit ULF fluctuations. These data suggest that 5577 emissions observed during a growth phase are initially due to non-accelerated plasma sheet particles but that an inverted-V develops gradually before substorm onset, forming a persistent, stationary arc. As this inverted-V precipitation slowly intensifies before onset (either in terms of particle energy or particle number flux or both), a measurable increase in ionospheric conductivity can be seen (by various instruments), presumably due to the inverted-V particle precipitation. Implications for substorm onset are discussed.