A high resolution spectral analysis of daily relative sunspot number and 10.7 cm. Solar flux

Abstract

Auto and cross-spectra of relative sunspot number and slowly varying component of solar radiation at 10.7 cm. have been computed for a 52-month period beginning September 1, 1958. Significant features of the spectra are relatively high variance at periods corresponding to one, three and four solar rotations. Statistically significant spectral peaks have been observed at three other frequencies and are ascribed to amplitude modulation of the 27-day component. The cross-spectral analysis indicates that during the period under investigation the solar 10.7 cm. flux leads the sunspot number for periods in excess of about 27.7 days; for shorter periods the flux lags behind the sunspot number. The coherence between the two time series, after an initial decrease from unity at zero frequency, assumes a maximum value of 0.985 at 27.7 days. The phase and coherence indicate that long-lived radio emission regions and spots appeared to co-rotate during 1958-62 with a period of 27.7 days.