Modelling solar irradiance variability on time scales from minutes to months

TL;DR

This paper models solar irradiance variability from minutes to months by combining convective and magnetic components, revealing how different scales are influenced by solar surface phenomena and offering insights into stellar granulation properties.

Contribution

It introduces a comprehensive model that separates granulation and magnetic effects to explain solar irradiance variability across multiple time scales.

Findings

Good match between model and solar data except at 10-30 hour periods

Magnetic activity influences variability on daily or longer scales

High-cadence data can reveal stellar granulation properties

Abstract

We analyze and model total solar irradiance variability on time scales from minutes to months, excluding variations due to p-mode oscillations, using a combination of convective and magnetic components. These include granulation, the magnetic network, faculae and sunspots. Analysis of VIRGO data shows that on periods of a day or longer solar variability depends on magnetic activity, but is nearly independent at shorter periods. We assume that only granulation affects the solar irradiance variability on time scales from minutes to hours. Granulation is described as a large sample of bright cells and dark lanes that evolve according to rules deduced from observations and radiation hydrodynamic simulations. Comparison of this model combined with a high time resolution magnetic-field based irradiance reconstruction, with solar data reveals a good correspondence except at periods of 10 to 30 hours. This suggests that the model is missing some power at these periods, which may be due to the absence of supergranulation or insufficient sensitivity of MDI magnetograms used for the reconstruction of the magnetic field-based irradiance reconstructions. Our model also shows that even for spatially unresolved data (such as those available for stars) the Fourier or wavelet transform of time series sampled at high cadence may allow properties of stellar granulation, in particular granule lifetimes to be determined.