Mechanisms for total and spectral solar irradiance variations

TL;DR

This paper reviews the current understanding of solar irradiance variations over different time scales, discussing observations, reconstruction methods, and the physical processes behind solar radiative output changes.

Contribution

It provides a comprehensive overview of observational data, reconstruction approaches, and the physical mechanisms driving solar irradiance changes across multiple wavelengths.

Findings

Semi-empirical models can reproduce the solar spectrum broadly.

Understanding physical processes is key to explaining irradiance variations.

Reconstruction approaches help interpret long-term solar variability.

Abstract

The total and spectral irradiance varies over short time scales, i.e. from days to months, and longer time scales from years to decades, centuries, and beyond. In this talk we review the current understanding of irradiance changes from days to decades. We present the current status of observations and discuss proposed reconstruction approaches to understand these variations. The main question that ultimately needs to be answered is what are the physical processes that could explain the enhanced heating of the photosphere, chromosphere, transition region, and corona, leading to a change in the solar radiative output at various wavelengths. As semi-empirical models allow us to reproduce the solar spectrum over a broad wavelength range, they offer a powerful tool to determine the energy necessary to heat certain layers and at the same time balance the radiative losses.