Empirical Modeling of Radiative versus Magnetic Flux for the Sun-as-a-Star

TL;DR

This study develops empirical models linking solar radiative flux to magnetic flux, revealing mostly linear relationships in chromospheric and coronal emissions, and demonstrates high predictive accuracy for spectral-irradiance variations.

Contribution

It introduces empirical models that relate radiative and magnetic flux, accounting for temporal components and variability, enhancing understanding of solar and stellar activity.

Findings

Models predict 85-90% of flux variability

Relationships are linear for chromospheric and coronal radiation

Temporal components explain part of flux variance

Abstract

We study the relationship between full-disk solar radiative flux at different wavelengths and average solar photospheric magnetic-flux density, using daily measurements from the Kitt Peak magnetograph and other instruments extending over one or more solar cycles. We use two different statistical methods to determine the underlying nature of these flux-flux relationships. First, we use statistical correlation and regression analysis and show that the relationships are not monotonic for total solar irradiance and for continuum radiation from the photosphere, but are approximately linear for chromospheric and coronal radiation. Second, we use signal theory to examine the flux-flux relationships for a temporal component. We find that a well-defined temporal component exists and accounts for some of the variance in the data. This temporal component arises because active regions with high magnetic field strength evolve, breaking up into small-scale magnetic elements with low field strength, and radiative and magnetic fluxes are sensitive to different active-region components. We generate empirical models that relate radiative flux to magnetic flux, allowing us to predict spectral-irradiance variations from observations of disk-averaged magnetic-flux density. In most cases, the model reconstructions can account for 85-90% of the variability of the radiative flux from the chromosphere and corona. Our results are important for understanding the relationship between magnetic and radiative measures of solar and stellar variability.