Total Solar and Spectral Irradiance Variations from Near-UV to Infrared

Abstract

AbstractTotal solar and UV irradiances have been measured from various space platforms for more than two decades. These measurements established conclusively that solar irradiance changes on a wide range of time scales: from minutes to the 11 years solar cycle. The first results on the spectral distribution of total irradiance variations have been provided by the SunPhotometers on the SOHO/VIRGO experiment at 402, 500, and 862 nm, showing that spectral irradiance at these particular wavelengths changes in a fashion similar to total irradiance with amplitudes being higher at the shorter wavelengths.Although considerable information exist on irradiance variations, their physical origin is not yet fully understood. Current empirical models assume that most of the irradiance variations can be explained by the effect of surface magnetic activity features, and it is assumed that there is a linear relation between solar indices and irradiance changes. In contrast, current results show that both UV and total irradiances were higher at the maximum of solar cycle 23 than magnetic indices, such as the sunspot number and the full disk magnetic field strength. In addition, there is a growing evidence that global effects, like temperature changes, may also contribute to irradiance variations. In this paper we give an overview of the current results on total and spectral irradiance variations, their relation to magnetic activity using measurements from the National Solar Observatory an Kitt Peak and SOHO-MDI. Climate implications of irradiance variations are also discussed.KeywordsSolar CycleSolar IrradianceTotal Solar IrradianceSpectral IrradianceSingular Spectrum AnalysisThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.