Continuing the Solar Irradiance Data Record with TSIS

The Total and Spectral Solar Irradiance Sensor (TSIS), first selected in 1998 for the National Polar-orbiting Operational Environmental Satellite System (NPOESS), re-manifested in 2010 on the NOAA-NASA Joint Polar Satellite System (JPSS), then the NOAA Polar Free Flyer, is now scheduled for deployment in 2017 on the International Space Station. The TSIS will acquire measurements of total and spectral solar irradiance (TSI and SSI, respectively). TSIS provides continuation of the Total Irradiance Monitor (TIM) and the Spectral Irradiance Monitor (SIM), currently flying on the NASA Solar Radiation and Climate Experiment (SORCE). Launched in 2003, SORCE is now more than eight years beyond its prime-mission lifetime. The launch failure of the NASA's Glory mission in 2011 coupled with diminished battery capacity on SORCE and delays in the launch of TSIS have put the continuous 38-year TSI record at risk. In 2012, a plan to maintain continuity of the TSI calibration scale between SORCE and TSIS was rapidly implemented through the USAF Space Test Program STPSat-3 that launched in late 2013. The shorter SSI record faces a likely gap between SORCE and TSIS. This paper summarizes the importance of highly accurate and stable observations of solar irradiance in understanding the present climate epoch and for predicting future climate; why continuity in the solar irradiance data record is required; improvements in the TSIS TIM and SIM, including verification of their calibration using ground-based NIST-traceable cryogenic standards; and how these improvements will impact Sun-climate studies in the near future.