Multispectral tomographic imaging of the midlatitude aurora

The CEDAR Optical Tomographic Imaging Facility (COTIF) consists of a midlat itude chain of meridional imaging spectrographs whose slit apertures subten d a common volume in the ionosphere. The facility provides a set of simulta neous multispectral brightness measurements that are used in a two-dimensio nal tomographic reconstruction (horizontal versus vertical) of auroral and airglow features in the midlatitude, subauroral ionosphere. A tomographic i nversion method is summarized which regularizes the vertical (field-aligned ) dimension using a nonlinear low-dimensional basis expansion. Three experi mental results are presented for atomic oxygen 557.7- and 630.0-nm emission s at midlatitude. Time sequences of the reconstructed emission fields illus trate the variability in O I excitation patterns in both the diffuse aurora and SAR arcs. The results are interpreted with respect to outstanding issu es associated with midlatitude aurora. Extracted vertical profiles are comp ared with published experimental and theoretical results.