Sporadic Na (Na,) layer events were frequently identified during 160 h of lidar observations at Arecibo in January, March and April 1989. Most were accompanied by sporadic E (E.) layers. The most spectacular Nas Es, event occurred on the night of 30-31 March when both the Na and electron abundances between 90 and 100 km increased by approximately 700% during a period of 2.25 h starting at 2100 LST. The maximum Na density was almost 42,000 cm3. The vertical and temporal structure of the Na and electron densities were remarkably similar during the event. The ratio of the average Na enhancement to the electron density varied from a maximum of 3.5 Na atoms/electron at 98 km to about 0.5 Na atoms/ electron below 94 km. Between 93 and 97 km the electron enhancement preceded the Na enhancement by 15-30 min. Above 97 km and below 93 km the Na and electron density variations were in phase. The data suggest that the Es, layer triggered the release of Na from a reservoir, but the Es layer was not the source of the major Nas layer. Two minor Nas layers were observed between 101 and 107 km after midnight LST which were also accompanied by intense s layers and enhancements of the O(1S) emission intensities. The abundances of these high altitude Nas layers were less than 1% of the electron abundances. These Na, layers appear to be caused by the conversion of Na in the Es layer to Na through a set of clustering reactions involving N2 CO2 and H2O.
ASJC Scopus subject areas
- Environmental Science(all)
- Atmospheric Science
- Earth and Planetary Sciences(all)