RUI: A Proposal for the Collection ad Analysis of Photometric Data Giving Solar Irradiance Fluctuations

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In the late 1970's and early 1980's two satellite experiments were launched to measure the solar irradiance, sometimes called the "solar constant". These two satellite experiments have shown quite clearly that the solar irradiance varies on time scales from minutes to years. The largest amplitude variations occur on time scales of 5 to 7 days and are clearly associated with the passage of large sunspot groups across the face of the sun. Ironically, the highest values of solar irradiance are during the peak of the solar cycle when the average area of sun spots is much larger than at other times. The enhanced irradiance near solar maximum may be due to the presence of large areas of faculae, magnetic field regions seen in white light near the limb as bright patches were thought to be too faint and too scarce to cause a significant change in solar irradiance compared to sunspots. The work at the SFO over the last six years has shown that faculae are indeed important sources of emission. In particular, it was shown for a group of large sunspots in 1982 that the emission from faculae approximately balanced the blocking of sunspots. The fragments of magnetic fields scattered across the sun, part of what is called the photospheric network, may be responsible for the surplus of emission that is seen at the time of the solar maximum. By obtaining accurate photometric images of the sun at various wavelengths, it is intended to determine the effects of sunspots, faculae and the network in the measurements of satellite irradiance monitors and permit the search for even more subtle solar effects. The results of this work may help to better predict the effects of the solar magnetic cycle on the earth's climate.