Response of solar irradiance to sunspot area variations

TL;DR

This study investigates whether long-term solar irradiance variability can be modeled using short-term proxies like sunspot area, finding that long-term changes cannot be reliably reconstructed from short-term responses due to nonlinearity and additional factors.

Contribution

The paper refines an empirical linear model of solar irradiance response to sunspot area by removing rotational effects and incorporating long-term variation terms, revealing limitations in proxy-based reconstructions.

Findings

Long-term variability cannot be reconstructed from short-term responses.

Solar response exhibits nonlinearity not correctable by simple rescaling.

Refined model improves understanding of solar irradiance dynamics.

Abstract

One of the important open questions in solar irradiance studies is whether long-term variability (i.e. on timescales of years and beyond) can be reconstructed by means of models that describe short-term variability (i.e. days) using solar proxies as inputs. Preminger and Walton (2005, GRL, 32, 14109) showed that the relationship between spectral solar irradiance and proxies of magnetic-flux emergence, such as the daily sunspot area, can be described in the framework of linear system theory by means of the impulse response. We significantly refine that empirical model by removing spurious solar-rotational effects and by including an additional term that captures long-term variations. Our results show that long-term variability cannot be reconstructed from the short-term response of the spectral irradiance, which cautions the extension of solar proxy models to these timescales. In addition, we find that the solar response is nonlinear in such a way that cannot be corrected simply by applying a rescaling to sunspot area.