Spectroscopic inversions of the Ca ii 8542 Ã line in a C-class solar flare

Abstract

We study the C8.4 class solar flare SOL2016-05-14T11:34 UT using high-resolution spectral imaging in the Ca ii 8542 à line obtained with the CRISP imaging spectropolarimeter on the Swedish 1-m Solar Telescope. Spectroscopic inversions of the Ca ii 8542 à line using the non-LTE code NICOLE are used to investigate the evolution of the temperature and velocity structure in the flare chromosphere. A comparison of the temperature stratification in flaring and non-flaring areas reveals strong footpoint heating during the flare peak in the lower atmosphere. The temperature of the flaring footpoints between continuum optical depth at 500~nm, $\log \ddot{\mathrm{I}}{„}_{500}\approx -2.5\mathrm{and}-3.5$ is $\sim 5-6.5\mathrm{kK}$, close to the flare peak, reducing gradually to $\sim 5\mathrm{kK}$. The temperature in the middle and upper chromosphere, between $\log \ddot{\mathrm{I}}{„}_{500}\approx -3.5\mathrm{and}-5.5$, is estimated to be $\sim 6.5-20\mathrm{kK}$, decreasing to pre-flare temperatures, $\sim 5-10\mathrm{kK}$, after approximately 15 minutes. However, the temperature stratification of the non-flaring areas is unchanged. The inverted velocity fields show that the flaring chromosphere is dominated by weak downflowing condensations at the Ca ii 8542 à formation height.

9 pages, 6 figures, accepted in ApJ