Deducing the reliability of relative helicities from nonlinear force-free coronal models

Julia K. Thalmann, X. Sun, K. Moraitis +1

We study the relative helicity of active region (AR) NOAA~12673 during a ten-hour time interval centered around a preceding X2.2 flare (SOL2017-09-06T08:57) and also including an e…