Auroral tomography analysis of a folded arc observed at the ALIS-Japan multi-station campaign on March 26, 1995

Auroral tomography is a state-of-the-art method to retrieve three dimensional (3D) structure of luminous aurora from images taken simultaneously at multiple observation points. Imaging is basically monochromatic and altitude structures as well as horizontal vortex structures at particular wavelength are reconstructed. These are crucial for quantitative understanding of auroral formation and dynamical processes. In March 1995,the first multi-point international campaign between Sweden and Japan was carried out using three unmanned Swedish ALIS stations (Kiruna, Merasjarvi, Tjautjas) and two Japanese sites (Abisko, Nikkaluokta), separated by about 50km in Kiruna region. ALIS stands for the Auroral Large Imaging System which aims at capturing large-scale composite auroral images as well as optical tomographic imaging by a computer-controlled networking. In this paper, a description is given on the analysis of auroral tomography on the reconstruction of folded auroral arc observed at 2340 : 30 UT on March 26,1995. The images are taken for 1-5s integration at a green line of 557.7nm. Cameras were pointed to one of the preset common field of view, viz., a core region which is just overhead of Kiruna. Optical tomography relying on inversion analysis by the algebraic reconstruction technique has been carried out. The result indicates a fold structure of auroral arc with inferred altitude profile of photo-emission peaking at around 120km.