Variations in the solar ultraviolet flux from July 13 to August 9, 1968

Abstract

Three simple photodiodes on the Spades satellite (1968-059A) have measured the near-earth solar flux in three broad wavelength intervals: 300–1150 A, 1150–1600 A, and 1600–2100 A. During the first 27 days of the satellite's lifetime, the signals in the two longer wavelength intervals showed nonrandom variations of more than 50% from the mean, and the short wavelength flux varied by 40%. Except for the 1150–1600 A channel, the variation did not correlate well with F10.7; all three channels showed a much stronger correlation with the area times intensity of calcium plage regions. The data are consistent with a model in which the effective plage temperature is about 1250°K higher than the background sun at all wavelengths in the 300–2100 A interval.