HR: 0800h
AN: SM51A-0279    [Abstracts]
TI: Nightside NEIAL Observations and their Relation to Boundary Auroral Features
AU: * Michell, R
EM: robert.g.michell@dartmouth.edu
AF: Dartmouth College, 6127 Wilder Laboratory, Hanover, NH 03755, United States
AU: Heinselman, C
EM: craig.heinselman@sri.com
AF: SRI International, 333 Ravenswood Avenue, Menlo Park, CA 94025, United States
AU: Nielsen, H
EM: hnielsen@gi.alaska.edu
AF: Geophysical Institute, University of Alaska Fairbanks, 903 Koyukuk Drive, Fairbanks, AK 99775, United States
AU: Lynch, K
EM: lynch@birkeland.dartmouth.edu
AF: Dartmouth College, 6127 Wilder Laboratory, Hanover, NH 03755, United States
AB: We present data from ground camera and radar observations of the aurora conducted from Poker Flat, Alaska during the winters of 2006 and 2007. The Radar observations were conducted using the Poker Flat Advanced Modular Incoherent Scatter Radar (AMISR). Dark auroral signatures in the camera data are found to occur with naturally enhanced ion acoustic lines (NEIALs) in the radar data. Observations of NEIALs are presented from two separate nights, displaying different auroral context. On 08 February 2007, one short-lived NEIAL event was observed with AMISR using high time-resolution (19 ms). These raw data reveal that the large returns associated with the NEIALs come from the dark region immediately adjacent to an active dynamic auroral arc. It was also found that propagation in altitude of the NEIALs occurs at or near the Alfven velocity. Furthermore, it was found that the enhanced up- and down-shifted shoulders of the NEIALs most often occurred independently of one another on a 19 ms timescale. On 31 March 2006, a moderately intense auroral arc, (10 kR at 557.7 nm), was located in the local magnetic zenith. During this event the radar observed 7 distinct periods of NEIAL activity. These times correspond to (a) when the polar cap boundary of the auroral arcs passed through the magnetic zenith and (b) when small-scale filamentary dark structure was present in the magnetic zenith. These observations are consistent with NEIALs occurring within the same auroral morphology which is known to contain broad-band extremely low frequency (BBELF) wave activity. These observations support the hypothesis that NEIALs and BBELF are differently observed aspects of the same auroral phenomenon. A relation between NEIALs and the in situ signature of BBELF wave activity, provides a link between the in situ measurements and the ground-based observations.
DE: 2407 Auroral ionosphere (2704)
DE: 2437 Ionospheric dynamics
DE: 2439 Ionospheric irregularities
DE: 2471 Plasma waves and instabilities (2772)
DE: 2704 Auroral phenomena (2407)
SC: SPA-Magnetospheric Physics [SM]
MN: 2007 Fall Meeting