| I investigate recent claims for a strong variation of clear-sky terrestrial solar irradiance with
solar activity (on the level of O(1%) over the 11-year cycle) derived from ground-based
observations of the Sun. As it turns out, these erroneous results arise because important
effects like the dimming by volcanic aerosols and long-term changes in atmospheric
transmission independent of solar activity have to be corrected for. After taking
these into account, clear-sky terrestrial solar irradiance can be shown to vary by
O(0.1%) as expected from satellite-based measurements of the changes in Total
Solar Irradiance over the solar cycle. On the one hand this example illustrates the
usefulness of ground-based monitoring of solar irradiance data, but on the other
hand it highlights the difficulties which can hamper an unbiased analysis of such
datasets.
References
Feulner, G., 2011: The Smithsonian solar constant data revisited: no evidence for a strong
effect of solar activity in ground-based insolation data, Atmos. Chem. Phys., 11,
3291–3301, doi:10.5194/acp-11-3291-2011
Feulner, G., 2013: On the relation between solar activity and clear-sky terrestrial
irradiance, Solar Phys., 282, 615–627, doi:10.1007/s11207-012-0129-z |