http://arxiv.org/abs/1504.06633

We study the effect of new emerging solar active regions on the large-scale magnetic environment of existing regions. We first present a theoretical approach to quantify the “interaction energy” between new and pre-existing regions as the difference between (i) the summed magnetic energies of their individual potential fields and (ii) the energy of their superposed potential fields. We expect that this interaction energy can, depending upon the relative arrangements of newly emerged and pre-existing magnetic flux, indicate the existence of “topological” free magnetic energy in the global coronal field that is independent of any “internal” free magnetic energy due to coronal electric currents flowing within the newly emerged and pre-existing flux systems. We then examine the interaction energy in two well-studied cases of flux emergence, but find that the predicted energetic perturbation is relatively small compared to energies released in large solar flares. Next, we present an observational study on the influence of the emergence of new active regions on flare statistics in pre-existing active regions, using NOAA’s Solar Region Summary and GOES flare databases. As part of an effort to precisely determine the emergence time of active regions in a large event sample, we find that emergence in about half of these regions exhibits a two-stage behavior, with an initial gradual phase followed by a more rapid phase. Regarding flaring, we find that newly emerging regions produce a significant increase in the occurrence rate of X- and M-class flares in pre-existing regions. Given the relative weakness of the interaction energy, this effect suggests that perturbations in the large-scale magnetic field, such as topology changes invoked the “breakout” model of coronal mass ejections, might play a significant role in the occurrence of some flares.

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Y. Fu and B. Welsch
Tue, 28 Apr 15
53/70

Comments: Submitted to Solar Physics