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 – 2.0×10 10 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 – 25×10 3 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 (Fe s ) layers was observed. These are the first observations of this phenomenon. The 2 largest Fe s 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 Fe s layers were as high as 31×10 3 cm −3 and the abundances were as high as 5.8×10 9 cm −2 . The observations are compared with previous measurements of mesospheric Fe and with recent observations of sporadic Na (Na s ) layers.