Chromospheric Velocities of a C-class Flare

TL;DR

This study utilizes high-resolution solar observations to measure chromospheric velocities during a C-class flare, revealing velocities up to 64 km/s and identifying periodic flare bursts, providing insights into flare dynamics and chromospheric evaporation.

Contribution

It presents the first high-resolution measurements of chromospheric velocities during a C-class flare, highlighting velocities higher than previous studies and detecting periodic flare bursts.

Findings

Velocities up to 64 km/s along flare ribbons

Detection of ~60 s periodic flare bursts

Observation of velocity direction changes at flare kernels

Abstract

We use high spatial and temporal resolution observations from the Swedish Solar Telescope to study the chromospheric velocities of a C-class flare originating from active region NOAA 10969. A time-distance analysis is employed to estimate directional velocity components in H-alpha and Ca II K image sequences. Also, imaging spectroscopy has allowed us to determine flare-induced line-of-sight velocities. A wavelet analysis is used to analyse the periodic nature of associated flare bursts. Time-distance analysis reveals velocities as high as 64 km/s along the flare ribbon and 15 km/s perpendicular to it. The velocities are very similar in both the H-alpha and Ca II K time series. Line-of-sight H-alpha velocities are red-shifted with values up to 17 km/s. The high spatial and temporal resolution of the observations have allowed us to detect velocities significantly higher than those found in earlier studies. Flare bursts with a periodicity of approximately 60 s are also detected. These bursts are similar to the quasi-periodic oscillations observed at hard X-ray and radio wavelength data. Some of the highest velocities detected in the solar atmosphere are presented. Line-of-sight velocity maps show considerable mixing of both the magnitude and direction of velocities along the flare path. A change in direction of the velocities at the flare kernel has also been detected which may be a signature of chromospheric evaporation.