Published online by Cambridge University Press: 13 May 2016
The long-term changes of the VIRGO radiometers have been re-analyzed in detail in order to resolve the puzzle of the early increase of the total solar irradiance (TSI) as observed by VIRGO. The exposure dependent changes can be described by a model which is based on a combination of an early increase of the sensitivity and a degradation with time which is modulated by the dose of solar UV radiation each detector receives. After correcting for the exposure-dependent behaviour both operational radiometers show an increase of their sensitivity which depends only on the time they are switched-on. After removing this increase the VIRGO TSI remains more or less constant during the minimum period of solar activity and reaches the solar maximum at levels comparable to the ones of former maxima.