Properties of localized, high latitude, dayside aurora

H. U. Frey, (1), T. J. Immel (1), G. Lu (2), J. Bonnell (1), S. A. Fuselier (3), 
S. B. Mende (1), B. Hubert (4), N. Ostgaard (1), and G. Le (5)

(1) Space Sciences Laboratory, University of California, Berkeley, USA.
(2) High Altitude Observatory, National Center for Atmospheric Research, 
    Boulder, USA.
(3) Lockheed Martin ATC, Palo Alto, USA.
(4) LPAP, Universite de Liege, Liege, Belgium.
(5) Laboratory for Extraterrestrial Physics, NASA Goddard Space Flight
    Center, Greenbelt, USA.


The FUV instrument on the IMAGE spacecraft frequently observes intense ultraviolet
(UV) emission from a localized dayside region poleward of the general auroral oval
location. One type of these emissions has been described as the signature of 
direct proton precipitation into the cusp after lobe reconnection during northward 
interplanetary magnetic field (IMF) and high solar wind dynamic pressure periods 
[Frey et al., 2002]. Here we describe a completely different type of high latitude 
aurora, which does not show any signature of precipitating protons. It also occurs 
during northward IMF conditions however, only during periods of very low solar 
wind dynamic pressure. It occurs at a much higher geomagnetic latitude than the 
normal cusp location and only during periods of positive IMF By . The intensity of 
the UV emission is somewhat anti-correlated with the solar wind dynamic pressure, 
much in contrast to the cusp emission. The brightness of the localized emission 
changes rapidly on time scales between 30 and 70 minutes without corresponding 
changes in solar wind properties. Coincident measurements by the FAST spacecraft 
verify that this is not the cusp, that ion precipitation is absent in these 
regions, and that strong precipitation of field-aligned accelerated electrons 
causes the aurora. We interpret this aurora as the optical signature of electron 
precipitation in the upward leg of a current system which closes the downward leg 
of the current system into the cusp in the ionosphere. 

_______________
J. Geophys. Res., 108(A4), 8008, doi:10.1029/2002JA009332, 2003.