Helioseismology: Observations and Space Missions

TL;DR

Helioseismology has significantly advanced our understanding of the solar interior through sensitive measurements and continuous observations enabled by ground networks and space missions, revealing insights into solar structure and magnetic activity.

Contribution

This paper provides a comprehensive overview of helioseismology techniques, instrumental developments, and key findings from long-term high-duty cycle observations.

Findings

Improved understanding of solar interior structure.

Detection of small surface fluctuations below 1 m/s.

Insights into solar magnetic activity over decades.

Abstract

The great success of Helioseismology resides in the remarkable progress achieved in the understanding of the structure and dynamics of the solar interior. This success mainly relies on the ability to conceive, implement, and operate specific instrumentation with enough sensitivity to detect and measure small fluctuations (in velocity and/or intensity) on the solar surface that are well below one meter per second or a few parts per million. Furthermore the limitation of the ground observations imposing the day-night cycle (thus a periodic discontinuity in the observations) was overcome with the deployment of ground-based networks --properly placed at different longitudes all over the Earth-- allowing longer and continuous observations of the Sun and consequently increasing their duty cycles. In this chapter, we start by a short historical overview of helioseismology. Then we describe the different techniques used to do helioseismic analyses along with a description of the main instrumental concepts. We in particular focus on the instruments that have been operating long enough to study the solar magnetic activity. Finally, we give a highlight of the main results obtained with such high-duty cycle observations (>80%) lasting over the last few decades.