Measurements of the total electron content and the equivalent slab thickness of the midlatitude ionosphere

The total electron content NT and the equivalent slab thickness T of the midlatitude ionosphere are determined from differential Doppler measurements on the radio transmissions from the Transit 4A satellite and the ionosonde data near Washington, D.C., and Ottawa. The trends of diurnal, seasonal, and sunspot cycle variations of NT and T at midday are describer!. It is found that in 1962 both NT and T were considerably decreased in magnitude as compared to the corresponding values near the peak of the sunspot cycle. The inferred mean electronion temperature is found to be generally in excess of the neutral gas temperature. The ratio Te/ Tg in the daytime is estimated to be 1.8 in summer and about 1.1 to 1.2 in winter, which may reflect corresponding changes in the ratio Q/N!, where Q is the heat input to the electrons and Ne is the electron density. The relationship between T and Kp appears to be rather ambiguous in contrast with the positive correlation between the neutral gas temperature and Kp.