Ionospheric scale height from the refraction of satellite signals.

Accurate observations of the elevation angle of arrival of 20 MHz signals from the polar orbiting satellite Beacon-B for a 20 month period have provided transmission ionograms which may be reduced to give Hp the scale height at the peak of the ionosphere. Noon seasonal averages of Hp are 1.35 (in winter) to 1.55 (in summer) times greater than the scale height obtained from bottom-side ionograms. A comparison of scale height at the peak with routine measurements of total content and peak electron density indicates that the O+/H+ transition level is above 1000 km during the day but comes down to about 630 km on winter nights. A predawn peak in the overall scale height is caused by a lowering of the layer to a region of increased recombination and is magnified in winter by low O+/H+ transition levels.