Measurements of electron cooling rates in the midlatitude and auroral-zone thermosphere

Two day-night pairs of thermosphere probe rockets, launched at Wallops Island, Virginia, in March 1965 and at Churchill, Manitoba, in November 1965 have provided altitude profiles of electron temperature and concentration at midday and midnight. Altitude profiles of N2 measured on the same four flights have in addition provided neutral gas temperature profiles. These data are employed to calculate electron cooling rate profiles, and these in turn are interpreted in terms of ionospheric heat sources. The daytime electron heat source for the F region, at both middle latitudes (L = 2.9) and in the auroral zone (L ≈ 8), appears consistent with solar ultraviolet heating. The nighttime F-region, however, appears to be heated by downward conduction from the protonosphere at middle latitudes and by particle heating in the auroral zone. The source of electron heating for the E region both day and night and at both locations cannot be explained by direct solar heating. This may be produced by neutral winds, electric currents, an unknown chemical reaction or, as Walker has suggested, selective heating of the electrons by excited N2 having lifetimes in the E region of the order of a day.