Very high altitude aurora observations with the Solar Mass Ejection Imager

[1] The Solar Mass Ejection Imager (SMEI) is a sensitive scanning instrument mounted on the Coriolis satellite that assembles an approximately all-sky image of the heliosphere in red-biased visible light once per orbit. Its lines of sight pass obliquely through the topside ionosphere and magnetosphere. We present serendipitous observations of a visual phenomenon detected at high altitudes ( >= 840 km) over the auroral zones and polar caps. The phenomenon is observed in two basic forms. The first, and more common, are periods of brief ( 1 - 3 min), nearly uniform illumination of the imager's field of view, which we interpret as transits of the satellite through a luminous medium. The second appear as localized filamentary structures, which we interpret as columns of luminous material, viewed from a distance, possibly extending to visible altitudes of 2000 km or higher. More than 1000 occurrences of these phenomena were recorded during the first full year of operations. These observations are well correlated in brightness and frequency with periods of enhanced geomagnetic activity.