Continuous Measurements of the Virtual Heights of the Ionosphere

This paper is a report of continuous measurements of the virtual heights of the ionized regions of the upper atmosphere. Short pulses of radio-frequency energy are sent out by a transmitter operating on 4100 kilocycles per second. The time interval required for the pulses to go up to the ionosphere and back is recorded photographically in the same room by means of an oscillograph. The revolving mirror of the oscillograph and the chopper wheel which makes the transmitter pulses are driven on the same shaft by a synchronous motor. Records are shown which indicate the variability, especially at night. In the morning and afternoon reflections come from the F region showing virtual heights around 240 kilometers. However, during the middle of the day the reflection often splits into two components and the 240-kilometer reflection becomes weak and disappears. The remaining component often rises during the middle of the day to 300 or 320 kilometers and then drops gradually to join the 240-kilometer component which reappears before sunset. Records are given which show the rapid appearance and disappearance of reflection at night from both the E and F regions. An increase in ionization is probably responsible for the reappearance of E reflections of the type shown. However, F reflections which gradually become strong at night may possibly be explained by recombination in the lower part of the F region which exposes a more strongly ionized upper part.