LIDAR OBSERVATIONS OF MESOSPHERIC FE AND SPORADIC FE LAYERS AT URBANA, ILLINOIS

Lidar measurements of mesospheric Fe were conducted at Urbana, IL (40°N, 88°W) during 4 nights in late October 1989. The average Fe abundances, layer centroid heights and rms widths varied between 1.0 – 2.0×1010 cm−2, 89.0 – 90.5 km and 3.2 – 4.1 km, respectively. The peak densities of the layer near 90 km varied between 15 – 25×103 cm−3. Considerable gravity wave and tidal activity was observed in the Fe profiles. On 3 nights the formation and dissipation of 3 large sporadic Fe (Fes) layers was observed. These are the first observations of this phenomenon. The 2 largest Fes layers formed at 102.4 km and 91.4 km over a period of about 20 min and their widths were approximately 2.3 km FWHM. The peak densities of the Fes layers were as high as 31×103 cm−3 and the abundances were as high as 5.8×109 cm−2. The observations are compared with previous measurements of mesospheric Fe and with recent observations of sporadic Na (Nas) layers. © 1990 by the Chinese Geophysical Society