Extraterrestrial solar irradiance variability: two and one-half years of measurements from nimbus 7

Abstract A cavity pyrheliometer aboard the Nimbus Spacecraft has been making solar irradiance measurements since 16 November 1978. The data has shown short term variability in the solar flux reaching the earth at the fractional percentage level. A long term downward trend at the 0.02 per cent per year level is also indicated. Inverse correlation between sunspot number and the measured irradiance has been found for a number of events. The data presented here is from a preliminary analysis through 13 July 1981.