Seasonal and sunspot cycle variations ofFRegion electron temperatures and protonospheric heat fluxes

Summary. The F region electron temperatures observed at Millstone Hill have been averaged to obtain the daytime (1000–1500 EST) and nighttime (2100–0300 EST) monthly average values for a 4½-year period (January 1964 through June 1968). A clear seasonal variation is found with summer daytime temperatures at 300 and 500 km, exceeding winter temperatures by an amount that increases with increasing sunspot activity. By contrast, the nighttime temperatures are greatest in winter and exhibit no sunspot cycle variation. The average daytime heat flux from the magnetosphere has been derived from these results and exhibits a clear trend of increasing with rising sunspot number. On the average, the daytime heat fluxes are 40% larger in winter than in summer. This variation is shown to be much greater than is expected on the basis of the observed change in the temperature of the (F region) heat sink alone. It is concluded that there is an annual variation in the temperature of the magnetosphere and that possibly this is brought about by an asymmetry in the photoelectron escape from northern and southern hemispheres.