EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Changing of the Guard for the Total Solar Irradiance Record

Greg Kopp, David Harber, Karl Heuerman, and Brandon Stone
Greg Kopp et al.
  • University of Colorado / LASP, United States of America (

The uninterrupted, 41-year-long, spaceborne total solar irradiance (TSI) record has recently undergone several changes in the instruments contributing to these measurements of the net incoming radiant energy providing nearly all the power driving the Earth’s climate system. Two long-term instruments, NASA’s SORCE/TIM and TCTE/TIM, have recently been powered off. This ends the 17-year record from the SORCE/TIM, which established the currently-accepted TSI value of 1361 W m‑2 after its launch in 2003. ESA’s SoHO/VIRGO continues to acquire measurements that extend its 24-year record, but data availability has been on hold as a new processing methodology is implemented. NASA’s recently-launched TSIS‑1/TIM is presently continuing the measurements of these stalwart legacy instruments. This new TSI instrument is demonstrating higher on-orbit accuracy than any prior such instrument has achieved, with daily measurement updates that are available to the community for climate- and solar-research purposes. I will discuss the many recent changes to the spaceborne TSI measurement record, the current measurement-accuracy improvements and stabilities achieved and their implications for Earth energy-balance studies, and the future plans to maintain measurement continuity.

How to cite: Kopp, G., Harber, D., Heuerman, K., and Stone, B.: Changing of the Guard for the Total Solar Irradiance Record, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11489,, 2020

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Presentation version 2 – uploaded on 06 May 2020
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  • CC1: Comment on EGU2020-11489, Miklos Zagoni, 06 May 2020

    Dear Greg, Thank you and congratulations for your excellent work.
    Which value would you recommend to use as the "true" or reference TSI at 1 AU:
    the SORCE (1360.68 W/m2) or the TSIS-1 (1361.14 W/m2) ?
    Thank you, Miklos.

    • AC1: Reply to CC1, Greg Kopp, 06 May 2020

      Hi Miklos, 

      The two instruments are within uncertainties of each other, and the difference is also small compared to the solar-cycle variations, so it doesn't matter a lot; but TSIS has the lower uncertainty, so weight its value more than SORCE's.

      Thanks, and I'm glad you're enjoying (and using) the data! Greg

  • CC2: Comment on EGU2020-11489, Benoit TOURNADRE, 06 May 2020

    Dear Greg,

    What would you recommend for spectral solar irradiance time series, for remote-sensing of multidecadal solar irradiance at the Earth's surface  ? Is NRLSSI2 a good candidate? Thanks,


    • AC2: Reply to CC2, Greg Kopp, 06 May 2020

      Hi Benoit,

      While they are both TOA, NRLSSI2 and SATIRE each give good SSI time series. They're both observation based, but, being models, extend beyond single instrument lifetimes and can be extended back in time for over 400 years. NRLSSI is more tied to actual observations; SATIRE more to physical modeling of the Sun.

      Best! Greg

  • CC3: Comment on EGU2020-11489, Miklos Zagoni, 06 May 2020

    Re "Maybe I should have used your LWCRE units!": 
    Dear Greg, from the four equations, two are for clear-sky, two for all-sky, and LWCRE connects them. That's why it works as the unit. Each global mean flux value is an integer on the intercepting cross-section disk: 15 reflected, 36 absorbed from TSI = 51 units in the all-sky, 8 reflected, 43 absorbed, 40 emitted, imbalance = 3 in the clear-sky); and the accuracy of LWCRE = 1 unit to your TSI is amazing: the best CERES mean LWCRE is 26.73 Wm-2, while with TSI = 51 units = 1361 Wm-2 we have LWCRE = 26.69 Wm-2. A difference of 0.04 Wm-2 ? Incredible precisity in climate science. ---- Thanks for your interest! Miklos.

Presentation version 1 – uploaded on 05 May 2020 , no comments