How strong is the effect of solar activity on clear-sky insolation on the ground?
Since space-based observations of Total Solar Irradiance (TSI) are available, we know that TSI varies by about 1 W/m2 (or 0.1%) between solar maxima and minima. This is also the variation one would expect for the clear-sky solar irradiance on the ground, unless there were some unknown effects by which solar activity could affect atmospheric transmission.
To test this hypothesis, I have analysed two sets of ground-based solar irradiance measurements from the Smithsonian Astrophysical Observatory and from Mauna Loa Observatory. After careful correction for seasonal variations and the effects of atmospheric aerosols, both records show that clear-sky terrestrial insolation varies by the same order of magnitude as the TSI above the atmosphere. Thus there is no evidence for any unknown effects of solar activity on atmospheric transmission.
As an example, the following graph shows the atmospheric transmission as a function of the sunspot number indicating no significant change of atmospheric transmission with solar activity:
No change in atmospheric transmission with solar activity (Feulner 2013).
Publications related to clear-sky irradiance variations
- Feulner G., 2013: On the relation between solar activity and clear-sky terrestrial irradiance, Solar Physics, 282 (Issue 2, February 2013), 615-627. doi:10.1007/s11207-012-0129-z Preprint
- Feulner G., 2011: Comment on "Strong signature of the active Sun in 100 years of terrestrial insolation data" by W. Weber, Annalen der Physik, 523 (Issue 11, November 2011), 946-950. doi:10.1002/andp.201100179
- Feulner G., 2011: The Smithsonian solar constant data
revisited: no evidence for a strong effect of solar activity in ground-based insolation data, Atmospheric Chemistry and Physics, 11 (Number 7, April 2011), 3291-3301. doi:10.5194/acp-11-3291-2011
