IMAGE-FUV Multispectral Observation of Theta Auroras
B. Hubert (1), J.-C. Gerard (1), S. B. Mende (2), H. U. Frey (2), T. J. Immel (2), 
M. Meurant (1) and V. Coumans (1)

1. Laboratoire de Physique Atmospherique et Planetaire,
Universite de Liege, Belgium.
2. Space Sciences Laboratory, University of California,
Berkeley, USA.

The theta aurora is an auroral structure presenting a sun-aligned transpolar arc. 
Five different dynamic evolution of the transpolar arcs are known, some of them 
being symmetrical to each other, leaving three basically different types of 
transpolar auroral features.

The theta aurora was previously studied with in-situ particles detectors onboard 
polar orbiting satellites and by ultraviolet imagers. Previous imaging works 
focused on the electron aurora. We use the FUV imagers onboard the IMAGE 
spacecraft to study separately the proton and electron contributions to the 
transpolar arcs at the global scale. The imagers of the IMAGE-FUV experiment 
remotely sense the electron aurora with the WIC and SI13 imagers observing 
respectively the N2-LBH and OI-135.6 nm emission, while the SI12 spectrographic
imager measures the Doppler-shifted Lyman-alpha proton precipitation.

The three different types of transpolar aurora will be analyzed using the 
IMAGE-FUV imagers. In particular, the relative contribution of proton and electron 
to the excitation of the theta aurora will be presented.

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To be presented at the 2002 Spring A.G.U. Meeting, 
Washington, D.C., U.S.A., 28-31 May 2002