Intercomparison of solar total irradiance data from recent spacecraft measurements

Abstract

Solar total irradiance data obtained by the solar monitors of the Earth Radiation Budget Experiment (ERBE) on board the Earth Radiation Budget Satellite (ERBS) and on the National Oceanic and Atmospheric Administration spacecraft NOAA 9 and NOAA 10 are compared with the solar total irradiance data obtained from the Solar Maximum Mission (SMM) Active Cavity Radiometer Irradiance Monitor 1 (ACRIM 1), the sounding rockets, and the Nimbus 7 Earth radiation budget (ERB) channel 10 C. For the first 2 years of solar total irradiance measurements in space, the ERBE solar monitors on board ERBS and NOAA 9 spacecraft yielded the same mean irradiance value of 1364.9 W m−2 for the solar constant. This value is 0.2% lower than the mean value of the solar constant derived from the SMM ACRIM 1 and the sounding rockets, and it is 0.4% lower than the Nimbus 7 ERB measurements. For the first 6 months of solar irradiance, data available from the ERBE solar monitor on board NOAA 10 spacecraft yielded a mean value of 1363.2 W m−2 for the solar constant. The current solar monitoring and ERB measurement programs have yielded solar total irradiance data of high accuracy and precision. The disparity between the solar total irradiance values obtained in near‐simultaneous measurements with absolute pyrheliometers of similar design and mode of operation is an indication of the uncertainty associated with absolute pyrheliometers available at present. This disparity points out the need for intercalibration of electrically self‐calibrating pyrheliometers from spacecraft to derive an absolute pyrheliometric scale, valid for solar total irradiance measurements from space.