Why isn't the solar constant a constant?

TL;DR

This study decomposes the total solar irradiance data over several decades to identify and quantify different components, revealing the complex variability mechanisms behind the so-called Solar Constant.

Contribution

It introduces a novel analysis using empirical mode decomposition and time-frequency analysis to separate and quantify the rotation, annual, and inter-solar-cycle signals in TSI data.

Findings

Rotation signal accounts for 42.31% of TSI variation.

Inter-solar-cycle signal accounts for 42.52%, linked to magnetic network elements.

Annual variation accounts for 15.17%, its origin remains unknown.

Abstract

In order to probe the mechanism of variations of the Solar Constant on the inter-solar-cycle scale, total solar irradiance (TSI, the so-called Solar Constant) in the time interval of 7 November 1978 to 20 September 2010 is decomposed into three components through the empirical mode decomposition and time-frequency analyses. The first component is the rotation signal, counting up to 42.31% of the total variation of TSI, which is understood to be mainly caused by large magnetic structures, including sunspot groups. The second is an annual-variation signal, counting up to 15.17% of the total variation, the origin of which is not known at this point in time. Finally, the third is the inter-solar-cycle signal, counting up to 42.52%, which are inferred to be caused by the network magnetic elements in quiet regions, whose magnetic flux ranges from $(4.27-38.01)\times10^{19}$ Mx.