Abstract
A detailed statistical analysis of F10.7 emission and its relation to manifestations of optical activity as evidenced by plages and sunspots has been carried out. The data were selected from days with complete radio and optical coverage during the years 1976 to 1982. Starting with individual peaks as shown by east–west scans at 10.7 cm, we find an excellent correlation (0.93) with the reported spot area for the individual active region (AR) from which the radio flux emanated. The correlation with the reported plage area is 0.84; the combination of plage and spot areas (0.96) only slightly improves the correlation with spot area alone. An equally close correlation of F10.7 exists with the 3/4 power of spot areas. These results suggest that the F10.7 emission is tightly bound to the magnetic flux of ARs. Center‐to‐limb variations indicate that the emitting region at 10.7 cm can be described as an optically thin volume with, in first order, spherical symmetry. Next, calculated on the basis of the sum of individual areas, one finds the expected total emission from the Sun for a carefully selected sample to be of comparable quality of correlation with spot and plage areas (0.88 and 0.80, respectively). Several tests were carried out to determine time variations of the reconstruction parameters, in particular, concerning a possible dependence of the optical data on the choice of observing station. We were unable to find in the data any evidence for the existence of a significant third component in the F10.7 emission, that is, a component that is not localized yet still follows roughly the solar cycle variation (network contribution). Finally, we compared for our sample days these findings with published daily indices for solar activity, that is, plage index and relative sunspot number, and conclude that the latter, with a correlation of 0.94, is overall the most trustworthy stand‐in for F10.7 data.
Published Version
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