Long-term Variation of the Corona in Quiet Regions

TL;DR

This study analyzes the long-term evolution of the quiet Sun's corona using Hinode EIS spectra, revealing that high-temperature emissions vary with the solar cycle despite stable electron densities.

Contribution

It provides new insights into how heat input to the quiet corona varies with the solar activity cycle, based on long-term spectral observations.

Findings

High-temperature emission lines vary with the solar cycle.

Cooler lines show reduced modulation over time.

Coronal electron density remains nearly constant.

Abstract

Using Hinode EUV Imaging Spectrometer (EIS) spectra recorded daily at Sun center from the end of 2006 to early 2011, we studied the long-term evolution of the quiet corona. The light curves of the higher temperature emission lines exhibit larger variations in sync with the solar activity cycle while the cooler lines show reduced modulation. Our study shows that the high temperature component of the corona changes in quiet regions, even though the coronal electron density remains almost constant there. The results suggest that heat input to the quiet corona varies with the solar activity cycle.