Interpretation of solar irradiance variations using ground-based observations
The contribution of solar magnetic features to the variation of the solar irradiance is investigated using ground-based observations. The disk integrated irradiance signal due to magnetic features is divided into two parts: the brightness excess, P, is interpreted as the facular contribution to the irradiance and the brightness deficit, N, as the sunspot contribution. The monochromatic data is least squares fitted to the active cavity radiometer irradiance monitor (ACRIM) data to transform our data to a bolometric quantity. The resulting fit shows that the facular irradiance contribution is nearly constant during 1980 while the sunspot contribution accounts for nearly all of the irradiance variations seen by the ACRIM experiment. The double-peaked facular contribution predicted by the Oster, Schatten, and Sofia (1982) photometric model is not seen in the data. If we average the data over one year, the presence of magnetic activity does not alter the irradiance from the zero activity level. This suggests that there is not an 11 year cycle in the solar irradiance; an upper limit to the amplitude of a possible 11 year cycle is set at 0.12%. Since the equatorward directed flux is nearly constant at all times, the presence of magnetic activity, due to the foreshortening of sunspots and the limb brightening of faculae, would increase the poleward directed flux, and thus, the solar luminosity.
- Research Organization:
- Mount Wilson and Las Campanas Observatories of the Carnegie Institution of Washington
- OSTI ID:
- 5668447
- Journal Information:
- Astrophys. J.; (United States), Vol. 267:2
- Country of Publication:
- United States
- Language:
- English
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