The electron heating rate and ion chemistry in the thermosphere above Wallops Island during the solar eclipse of 7 March 1970

Abstract

An identical pair of thermosphere probes measured the N 2 concentration and temperature, the ion composition and concentrations and the electron temperature up to 290 km about 30 min and 5 min before totality during the 7 March 1970 eclipse at Wallops Island. The rockets travelled similar trajectories thus permitting the purely temporal changes between nights to be resolved. The neutral temperature and N 2 concentration changed little but the electron temperature decreased by as much as 20 per cent in the lower F-region. The ion concentration decreased by about 30 per cent in the F-region and about 50 per cent in the E-region, with little change in relative ion composition. The electron cooling rates decreased by a factor of 6 in the lower F-region, approximately in proportion to the change in visible solar disc. A smaller than expected decrease in the cooling rate below 150 km between the two flights indicates a hardening of the solar spectrum and suggests a significant heat contribution from the solar corona near totality. The ion composition measurements were consistent with solutions of the ion continuity equations. A proper fit required a factor of three enhancement of the flux below 200 Å, an amount also consistent with the electron heat balance analysis. Reactions involving the minor ions N + and N 2 + were found to be important for the ion chemistry of the major ions O 2 + and NO +, especially at the time of eclipse. The negligible response of the neutral atmosphere to the eclipse is reasonable considering the long time constants for the conductive and convective transport processes and the local nature of the disturbance.