On the Relation between Solar Activity and Clear-Sky Terrestrial Irradiance

TL;DR

This study analyzes Mauna Loa solar irradiance data from 1958-2010 to examine the relationship between solar activity and terrestrial insolation, finding minimal variation and no significant trend with sunspot number.

Contribution

It provides a detailed correction and analysis of long-term irradiance data, demonstrating that clear-sky terrestrial irradiance varies little with solar activity and lacks evidence of unknown amplifying effects.

Findings

Clear-sky terrestrial irradiance varies by about 0.2% over the solar cycle.

No significant trend in atmospheric transmission with sunspot number.

Long-term atmospheric transmission shows effects of volcanic aerosols and other factors.

Abstract

The Mauna Loa Observatory record of direct-beam solar irradiance measurements for the years 1958-2010 is analysed to investigate the variation of clear-sky terrestrial insolation with solar activity over more than four solar cycles. The raw irradiance data exhibit a marked seasonal cycle, extended periods of lower irradiance due to emissions of volcanic aerosols, and a long-term decrease in atmospheric transmission independent of solar activity. After correcting for these effects, it is found that clear-sky terrestrial irradiance typically varies by about 0.2 +/- 0.1% over the course of the solar cycle, a change of the same order of magnitude as the variations of the total solar irradiance above the atmosphere. An investigation of changes in the clear-sky atmospheric transmission fails to find a significant trend with sunspot number. Hence there is no evidence for a yet unknown effect amplifying variations of clear-sky irradiance with solar activity.