IMAGE-FUV multispectral observation of theta auroras.

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 N[SUB]2[/SUB]-LBH and OI-135.6 nm emission, while the SI12 spectrographic imager measures the Doppler-shifted Lyman-ë± emission which is solely due to the auroral 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.