The CEDAR Optical Tomographic Imaging Facility (COTIF) consists of a midlatitude chain of meridional imaging spectrographs whose slit apertures subtend a common volume in the ionosphere. The facility provides a set of simultaneous multispectral brightness measurements that are used in a two-dimensional tomographic reconstruction (horizontal versus vertical) of auroral and airglow features in the midlatitude, subauroral ionosphere. A tomographic inversion method is summarized which regularizes the vertical (field-aligned) dimension using a nonlinear low-dimensional basis expansion. Three experimental results are presented for atomic oxygen 557.7- and 630.0-nm emissions at midlatitude. Time sequences of the reconstructed emission fields illustrate the variability in O I excitation patterns in both the diffuse aurora and SAR arcs. The results are interpreted with respect to outstanding issues associated with midlatitude aurora. Extracted vertical profiles are compared with published experimental and theoretical results. ¿ 1999 American Geophysical Union