We present case studies of the mesospheric alkali and non-alkali metals, Na and Fe, along with electron concentrations [Ne] obtained from measurements made at Arecibo on nights of 17-18 and 18-19 March 2004. The background mesospheric conditions as recorded by an airglow all-sky imager displayed ripple- and band-type structures on these nights. Both of the metals display detailed structures within their neutral sporadic layer but are more pronounced in Na than for Fe. A sporadic-E (Es) with electron concentrations [Ne] exceeding 3000 electrons cm-3 is accompanied by a strong Na enhancement and a weak sporadic Fe (Fes) layer around 95-km altitude. The concentration of Fe+ and Na+ is estimated to be close to 600 and 30 ions.cm-3, respectively, within the sporadic-E layer. In order to investigate ion-neutral coupling, a correlative analysis was performed in two altitude regions. Similar features are seen between neutrals and electrons in the 96-100-km altitude range, while within the altitude range of 80-90 km, an opposite behavior is seen. A comparative study between neutral layers below 90 km often referred to as the main or permanent layer and sporadic activity above 90 km reveals different characteristics for alkali and non-alkali metal. Fe concentrations in the main layer are higher than in Fes resulting in a density ratio of less than 1 determined from two layers of 3 km thickness centered at 97 and 87 km. For the case of Na, the ratio exceeds 1 during Es activity on both the nights. The case studies discussed in this work facilitate our understanding of different factors that can influence the sporadic activity in alkali and non-alkali. In a region dominated by ion-molecule chemistry, temperature fluctuations that can be induced by wave activity will have more impact on Na than for Fe within their layers depending on altitude.
All Science Journal Classification (ASJC) codes
- Space and Planetary Science