IMAGE and FAST observations of substorm recovery phase aurora

Stephen B. Mende, Harald U. Frey, Charles W. Carlson, J. McFadden, 
Jean-Claude Gerard, Benoit Hubert, Stephen A. Fuselier, G.R. Gladstone 
and James L. Burch


Images from the IMAGE Wide-band Imaging Camera (WIC) and Spectrographic Imager
(SI) channel SI12, were compared to in situ data taken by FAST. The IMAGE data
segment began during the expansive phase of a substorm and a double oval
configuration evolved, consisting of a set of discrete poleward auroral forms
and a separate more diffuse oval. The FAST data showed that a narrow (~1.5
degree latitude) region of downward currents separated the two ovals. The SI-12
optical observations showed a single oval of precipitating protons located on
the equatorward side within the diffuse aurora. In agreement with IMAGE, the
highest intensity proton flux measured by FAST was concentrated on the
equatorward region although low flux protons were present throughout the entire
double oval. In the lower latitude diffuse oval occasional structured auroras
were embedded. These structured auroras were mostly created by inverted V type
electrons but there were narrow regions in which intense beams of accelerated
electrons were seen whose energy/pitch angle distribution and accompanying
electric field data were consistent with Alfven wave acceleration. The poleward
oval consisted of an intense inverted V precipitation event poleward of which a
weak region of Alfven wave accelerated electrons was located. From the images it
appears that the Alfven wave accelerated electron event in the diffuse auroral
regions and the poleward features were part of short lived or rapidly moving
auroral forms. 

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Geophysical Research Letters, 29, 10.1029/2001GL013027, 2002