Ionic composition and temperature over Arecibo 2

Abstract

Results on the composition and temperature of the charged particles in the topside ionosphere over Arecibo, as obtained from the analysis of incoherent backscatter spectra gathered at the Arecibo Ionospheric Observatory during the period December 1965 through October 1967, are presented. Enhanced solar activity resulted in increased concentration of the heavier oxygen ions and thereby higher altitude for the O+ → He+ and H+ transition level. The oxygen ions were important over a larger altitude range in summer than in winter. On winter nights the oxygen ion concentration began to rise even before local sunrise and continued to build up to early afternoon hours. In summer, however, the O+ concentration levels off within about two to three hours of sunrise. A marked altitude gradient in temperature existed during winter nights when some thermal nonequilibrium also was noticeable. In contrast, the entire ionosphere was practically isothermal during summer nights.