Absorption of cosmic radio noise at 22.2 Mc/sec following solar flare of February 23, 1956

Reports of widespread ionospheric disturbances on the dark hemisphere of the earth, accompanying the great solar flare of February 23, 1956, have been noted by a number of groups. A. Shapley has reported an increase in ionospheric absorption at vertical sounding stations in high latitudes,1 commencing a few minutes after the flare and lasting many hours, while Ellison and Reid,2 and Gold and Palmer,3 have reported a sudden decrease in 27-kc/sec atmospherics at the time of the flare, coming too early and much too suddenly to be due to sunrise effect. In the auroral zone, effects were noted by the Geophysical Institute at College, Alaska,4 whose records of galactic radio noise at 30 Me/sec showed an increase in absorption shortly after the flare, increasing gradually to a maximum of 1.8 db over the period 04h 20m to 09h 00m UT. Absorption effects of a different nature have been found on radio-source records taken at the Seneca Radio Observatory of the Carnegie Institution, near Washington, D.C. The equipment consisted of a phase-switching interferometer5 tuned to 22.2 Me/sec, utilizing a pair of small antennas which were normally used for observations of the planet Jupiter, but which observe a number of other radio sources as well. Comparison of the record obtained near the time of the flare with a record taken the previous night showed a noticeable difference for a short period when Virgo A (IAU 12NlA) was being observed. The apparent intensity of the source on February 23 compared to the intensity of the previous night is shown in Figure 1. The horizontal lines give the relative intensity, averaged over the period indicated by the length of the line. Since the observation was made with a phase-switching interferometer which gives zero output when the source is near quadrature in the interference pattern, the averages were taken over the peaks, when the source is near a maximum or minimum in the interference pattern.