The first results of an investigation of the altitude characteristics of auroral echoes at 398 MHz are presented. The data were collected over two nights in the spring of 1973 with a phased array radar operated at Homer, Alaska. Heights of maximum backscattered power can be determined with an accuracy approaching 2 km, a temporal resolution as short as 20 s, and a horizontal spatial resolution of 40 km. The spatial distributions of the height of echoing in two premidnight periods are shown to be consistent with a model of scattering from a continuous range of heights between 97 and 117 km; within this interval, the height tends to change in such a way that the echoes come from directions nearly perpendicular to the earth's magnetic field. In a postmidnight period, the echo activity was confined to a region of considerably more restricted (5–10 km) vertical extent. In all cases, the echo region was sharply bounded from below at 96–98 km. The heights may have short-term (minutes) and small-scale (< 100 km) structure. Adjacent structures are sometimes observed to differ in height by as much as 10 km.
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