Spectroscopic Inversions of the Ca ii 8542 Å Line in a C-class Solar Flare

We study the C8.4-class solar flare SOL2016-05-14T11:34 UT using high-resolution spectral imaging in the Ca ii 8542 Å line obtained with the CRISP imaging spectropolarimeter on the Swedish 1 m Solar Telescope. Spectroscopic inversions of the Ca ii 8542 Å line using the non-LTE code NICOLE are used to investigate the evolution of the temperature and velocity structure in the flaring 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 $\mathrm{log}\,{\tau }_{500}\,\approx -2.5\,\mathrm{and}\,-3.5$, where τ 500 is the continuum optical depth at 500 nm, is $\sim 5\mbox{--}6.5\,\mathrm{kK}$ close to the flare peak, reducing gradually to $\sim 5\,\mathrm{kK}$. The temperature in the middle and upper chromosphere, between $\mathrm{log}\,{\tau }_{500}\approx -3.5$ and −5.5, is estimated to be ~6.5–20 kK, decreasing to preflare temperatures, ~5–10 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 formation height of Ca ii 8542 Å.