Simultaneous observations of sporadic <i>E</i>, Na, Fe, and Ca⁺ layers at Urbana, Illinois: Three case studies

Abstract

We describe three sporadic layering events observed in the mesospheric metal layers above Urbana, Illinois, using resonance fluorescence lidars and an MF radar. On June 6–7, 1991, a sporadic Na layer and a prominent temperature inversion layer were observed near 90 km. The formation of this low‐altitude event appears to involve the release of Na from a chemical reservoir or from the surfaces of dust and smoke particles, perhaps facilitated by the high temperatures in the inversion layer. On December 10, 1991, sporadic Fe and Ca + layers formed near 94 and 95 km, respectively, and on December 17–18, 1991, sporadic E , Fe, Na, and Ca + layers formed simultaneously near 100 km. The characteristics of these December events suggest that sporadic Fe and high‐altitude sporadic Na layers are formed by the neutralization of Fe + and Na + in the associated sporadic E layers.