Variations in total solar and spectral irradiance as measured by the VIRGO experiment on SOHO

Abstract

The Variability IRradiance Gravity Oscillation (VIRGO) experiment on SOHO has been observing total solar and spectral irradiances at 402 nm (blue channel), 500 nm (green channel), and 862 nm (red channel) since January 1996. The VIRGO observations have shown that solar active regions influence both total and spectral irradiances in a similar fashion, although the amplitude of the variations seems to be the largest for the near-UV and visible wavelengths. Comparison of the VIRGO total solar irradiance and the UARS/SUSIM Mg II h & k core-to-wing ratio shows that total irradiance started to rise in prior to UV irradiance, as represented by the Mg core-to-wing ratio. In this paper we review the most recent results on the VIRGO irradiance variations related to solar activity. We dedicate this paper to the memory of Dr. Guenther Brueckner, the late Principal Investigator of the UARS/SUSIM experiment, who will always remain in the heart and memory of the authors of this paper.