VLF phase shifts associated with the disturbance of February 23, 1956

During the magneto-ionic disturbance following a solar flare at about 03h 34m U.T. on February 23, 1956, the phase of a signal received at Cambridge, Massachusetts, at 16 kc/s from a transmitter, at Rugby, England, was advanced by about 44 microseconds or 250°. The peak Doppler effect on the received frequency occurred at 03h 47m, and corresponded approximately to a falling of the effective height of reflection at 1 km/min, assuming that the phase change was produced solely by a change in height. The record of this phenomenon is contrasted with those made during daytime sudden ionospheric disturbances. It is shown that in the latter case an increase in signal amplitude is observed at 60 kc/s but not at 16 kc/s, and that there must be changes in the phase shift at reflection from the ionosphere, as well as changes in the height of reflection. Some comparisons are given between the time of occurrence of this phenomenon and the times of various other effects of this disturbance that have already been reported.