Fredagskollokvium: What is the value of the Total Solar Irradiance?

Bo Andersen, solar physicist and member of the Framsenter in Tromsø.

portrettbildet av Bo Andersen

Bo Andersen, Dr.Scient in solar physics from ITA, steering board leader of Framsenter in Tromsø.

Foto: Norsk Romsenter

The understanding of the value and the variation of the TSI is threefold important: to understand the energy generation and internal energy transport of the Sun, to use the TSI in comparing the Sun to other stars, to understand the impact on the Earths climate.

TSI requires an absolute measurement, we want the value in W/m2 at mean Sun-Earth distance. The accuracy requirement is such that only space measurements can achieve it. There are several technological issues that make the design of the instruments difficult in order to know both the sensitivity and stability of each instrument. Clear differences in sensitivity and stability have been observed at an unacceptable level to be able to study variations over several solar cycles.

Instruments providing data from different times must be stitched together. Here there are controversies that have impact on what influence the solar cycle variation of TSI may have on the Earths climate. Many different groups have attempted to model the interdependence of TSI and other solar phenomena during the solar cycle.

In this talk, I will among other issues concerning TSI measurements, present my own results studying only the effects around the solar activity minima. The reason for this is that the connection between TSI and other solar phenomena may be different at high compared to low solar activity.

graph showing the total solar irradiance during years of time.
These are most of the raw data sets, how do we disentangle these seemingly contradictory data to find the absolute value of the TSI over time? Credits: G. Kopp 2019.

Bo Andersen

  • Bo Andersen has a Cand.real and Dr.Scient in solar physics from ITA with data from the Oslo Solar Observatory. He has worked in ESA ESTEC where he co-designed the VIRGO experiment on SOHO.
  • From 1988 to 2020 he worked at the Norwegian Space Agency, twelve of these years as Director General. Currently he does consultant work and is the steering board leader of the Framsenter in Tromsø.
  • He has close to a hundred publications, mostly in helioseismology

Please join via Zoom at

Meeting ID: 652 4639 3883
Passcode: 784319

Attendees will be muted during the colloquium, but will have the opportunity to ask questions at the end by clicking on the "raise hand” button (or send a request to me via chat).


Institutt for teoretisk astrofysikk
Emneord: helioseismology, solar physics, Friday colloquium, fredagskollokvium, Solfysikk
Publisert 4. des. 2020 13:51 - Sist endret 15. jan. 2021 10:08