Simultaneous observations of sporadic E, Na, Fe, and Ca⁺ layers at Urbana, Illinois: three case studies

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 Fe²⁺ and Na⁺ in the associated sporadic E layers. -from Authors