The development of lower-atmosphere turbulence early in a solar flare

TL;DR

This study observes the early development of turbulence in the lower solar atmosphere during a flare, revealing turbulence precedes flare onset and influences energy transport, challenging existing models.

Contribution

First observational evidence of turbulence onset in the lower solar atmosphere during a flare at high temporal resolution.

Findings

Nonthermal spectral line broadening precedes flare onset.

Turbulence oscillates with a ~10 s period during the flare.

Turbulence contributes to heating the lower atmosphere.

Abstract

We present the first observational study of the onset and evolution of solar flare turbulence in the lower solar atmosphere on an unprecedented time scale of 1.7 s using the Interface Region Imaging Spectrograph observing plasma at a temperature of 80,000 K. At this time resolution, nonthermal spectral line broadening, indicating turbulent velocity fluctuations, precedes the flare onset at this temperature and is coincident with net blue-shifts. The broadening decreases as the flare brightens and then oscillates with a period of ~10 s. These observations are consistent with turbulence in the lower solar atmosphere at the flare onset, heating that region as it dissipates. This challenges the current view of energy release and transport in the standard solar flare model, suggesting that turbulence partly heats the lower atmosphere.