Changes in ionization and radio reception during the sunspot period 1944-1947.

Abstract

If 12-month running means of critical frequencies are taken to eliminate seasonal effects, a close correspondence exists between critical frequencies for both the E- and F-layers and sunspots. Since the ultra-violet light of the Sun is assumed to be the major ionizing agent, this increase in ionization with sunspots during the night hours presents some interesting cosmic problems as to the cause and the maintenance of ionization on the unilluminated half of the Earth. Standardized measurements of field intensities of the Bureau of Standards standard-frequency signal, WWV, have been recorded at the Cosmic Terrestrial Research Laboratory at Needham during recent years for the 5-, 10-, and 15-Mc frequencies. Curves of night fields of WWV-5-Mc show that during the rise of sunspots from 1945 to 1947 the average values recorded between 22h and 02h rose from 300 microvolts to 900 microvolts when the Zurich sunspot-nurnber of 105 was reached; thereafter, field intensities decreased in value as sunspot-numbers continued to rise to a maximum of 150, a value reached last year. The decline in field strength with very high sunspot-numbers is attributed to attenuation introduced by increase ionization of the lower layers. Day fields, representing averages of observations between 10h and 14h showed a steady decline with increasing sunspots, a fact which is again explained on the basis of increasing absorption in the lower layers. The changes in the daytime field were from 225 microvolts when the sunspot-number was 20 to about 15 microvolts when sunspot-numbers were 150. For the 10-Mc reception day fields rose from a value slightly in excess of 90 microvolts, when the sunspot-number was 80, to values of 260 microvolts or more, when sunspot-numbers registered from 140 to 150. Night fields on the 10-Mc frequency, based on observations between 22h and 02h, rose from 10 microvolts, with sunspot-number of 80, to values in excess of 30. microvolts, with sunspot-numbers between 140 and 150. Observations on the broadcast band of Station WBBM, Chicago, 780 kc, received at Needham, a distance of 851 miles, show a general decline in field intensities from values in excess of 270 microvolts to values of but 45 microvolts as sunspot-numbers increased from 20 to a maximum value of 150.