  We study the effect of newly emerged solar active regions (ARs) on the
large-scale magnetic environment of pre-existing ARs (PEARs). We first present
a theoretical approach to quantify the "interaction energy" between new ARs and
PEARs 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 PEAR 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 PEAR 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 ARs on flare statistics in
PEARs, using NOAA's Solar Region Summary and GOES flare databases. As part of
an effort to precisely determine the emergence time of ARs 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 the emergence of new ARs is associated
with a significant increase in the occurrence rate of X- and M-class flares in
PEARs. This effect tends to be more significant when PEARs and new emerging ARs
are closer. Given the relative weakness of the interaction energy, this effect
suggests that perturbations in the large-scale magnetic field, such as topology
changes invoked in the "breakout" model of coronal mass ejections, might play a
significant role in the occurrence of some flares.

Solar and Stellar Astrophysics