The Influence of Solar Flares on the Lower Solar Atmosphere: Evidence from the Na D Absorption Line Measured by GOLF/SOHO

TL;DR

This study provides statistical evidence that solar flares influence the Na D absorption lines, indicating dynamic plasma motions in the lower solar atmosphere during flare events, based on ten years of GOLF/SOHO data.

Contribution

It demonstrates that solar flares impact the Na D lines and reveals plasma motion directions during flares using long-term observational data.

Findings

Na D line asymmetry varies during flares

Upward plasma motion occurs at flare peaks

Downward motion follows the peak

Abstract

Solar flares presumably have an impact on the deepest layers of the solar atmosphere and yet the observational evidence for such an impact is scarce. Using ten years of measurements of the Na D$_{1}$ and Na D$_2$ Fraunhofer lines, measured by GOLF onboard SOHO, we show that this photospheric line is indeed affected by flares. The effect of individual flares is hidden by solar oscillations, but a statistical analysis based on conditional averaging reveals a clear signature. Although GOLF can only probe one single wavelength at a time, we show that both wings of the Na line can nevertheless be compared. The varying line asymmetry can be interpreted as an upward plasma motion from the lower solar atmosphere during the peak of the flare, followed by a downward motion.