Evidence of Horizontal Motion in Region F2 Ionization

Abstract

DURING the winter periods of 1942 and 1943, a series of relative field-strength measurements were made at the Radio Research Station, Slough, on signals from the German short-wave sender Zeesen situated 990 km. east of Slough1. Subject to the assumption that local time variations corresponded with longitude variations in the ionosphere, it was observed that the time of the initial appearance of the oblique ray signal at sunrise agreed closely with the value to be expected from calculations based on normal incidence ionospheric observations at Slough2. These sharp sunrise variations in the ionosphere occurred at Slough some thirty minutes later than at the mid-point of the oblique trajectory; this corresponds closely to the local time difference between Slough and this mid-point. It was noted, however, that in addition to these regular sunrise ionospheric changes of large magnitude, there were small irregularities in the F2 layer occurring near the mid-point of the oblique trajectory, which were repeated overhead at Slough some 60–75 minutes later.