Changes of Magnetic Energy and Helicity in Solar Active Regions from Major Flares

We have characterized the evolution of magnetic energy and helicity associated with 23 X-class flares from 2010 to 2017. Our sample includes both confined and eruptive events, with 6 and 17 in each category, respectively. Using HMI vector magnetic field observations from several hours before to several hours after each event, we employ (a) DAVE4VM velocity estimates to determine the photospheric fluxes of energy and helicity and (b) non-linear force-free field (NLFFF) extrapolations to estimate the coronal content of energy and helicity in source-region fields.

Using Superposed Epoch analysis (SEA), we find, on average: (1) decreases in both magnetic energy and helicity, in both photospheric fluxes and coronal content, that persist for a few hours after eruptions, but no clear changes for non-eruptive events; (2) increases in photospheric twist in both eruptive and non-eruptive fields after events, though non-eruptive fields have lower twist overall; and (3) on longer time scales (event time + 20 hours), replacement of energy and helicity content to near pre-event levels for eruptive events. For eruptive events, we also investigate relationships between changes in helicity from post- versus pre-event extrapolations and the expected helicity present in erupted flux ropes derived from the observed reconnected flux in each flare.