Iron atom densities in the polar mesosphere from lidar observations

Between March 24 and April 6, 1990, we performed lidar measurements of iron densities above Andøtya, Norway (69° N). In each of the five nights of measurements we observed a regular Fe layer which was confined to the altitude region between 80 and 100 km. Its peak Fe densities occurred at (84.5 ±1) km or approximately 6 km lower than the peak of the sodium layer as observed by us two weeks earlier. The regular Fe layer exhibited column densities of (9 ± 4) ·10 9 cm −2 and maximum number densities close to 7,000 cm −3 . In addition, sporadic Fe layers were observed frequently between 88 and 108 km, one of which reached a maximum number density of 78,000 cm −3 near 97 km altitude. Properties of the Fe layers as observed by us are compared to those observed by Granier et al. [1989] and by Bills and Gardner [1990].