Applying the weighted horizontal magnetic gradient method to a simulated flaring Active Region

Here, we test the weighted horizontal magnetic gradient ($WG_M$) as a flare

precursor, introduced by Korsos et. al. (2015, ApJ, 802, L21), by applying it

to a magneto-hydrodynamic (MHD) simulation of solar-like flares Chatterjee et.

al. (2016, Physical Review Letters, 116, 10, 101101). The pre-flare evolution

of the $WG_M$ and the behavior of the distance parameter between the

area-weighted barycenters of opposite polarity sunspots at various heights is

investigated in the simulated $\delta$-type sunspot. Four flares emanated from

this sunspot. We found the optimum heights above the photosphere where the

flare precursors of the $WG_M$ method are identifiable prior to each flare.

These optimum heights agree reasonably well with the heights of the occurrence

of flares identified from the analysis of their thermal and Ohmic heating

signatures in the simulation. We also estimated the expected time of the flare

onsets from the duration of the approaching-receding motion of the barycenters

of opposite polarities before each single flare. The estimated onset time and

the actual time of occurrence of each flare are in good agreement at the

corresponding optimum heights. This numerical experiment further supports the

use of flare precursors based on the $WG_M$ method.