Rocket electron concentration measurements on winter days of normal and anomalous absorption

Lower ionosphere electron concentration profiles from rocket measurements are compared from a normal winter day, December 15, 1965, and from a winter day of anomalous absorption, January 10, 1966. Enhancements of electron concentration are found on the anomalous day relative to the normal day, from 60 to 95 km altitude, ranging up to a factor of 47 at 85 km. These enhancements in electron concentration are shown to be the direct cause of the increased absorption; although the electron collision frequency increased by a small amount, its contribution is relatively insignificant. The rocket measurements are shown to be consistent with measurements of electron concentration and absorption from sweep-frequency and fixed-frequency ionosondes.