A constant-α force-free-field analysis of the active region AR 4711 of February, 1986

The theory of Yang, Chang, and Harvey (1983) is used to perform this analysis of the big active region AR 4711 of February, 1986, which produced many big and strong flares with proton events, SIDs and other significant geophysical effects. The various physical quantities are calculated, yielding for ∆M a value up to 5.36 × 10³² erg, sufficient to supply the energies of the observed flare activities in this active region. Observations of the twisting of the entire quadrupolar sunspot group and the variations of the magnetic energies with dates all agree with our theoretical expectations. It is found that the maximum of the f number of flare activity occurred about one day later than the maximum of ∆M, i.e., the release of free magnetic energy to produce flare activity requires a time interval of about one day. This, together with the formula of ∆M can be useful in solar prediction work. Similar to the famous active region of August 1972 (McMath 11976), the separation of both footpoints of the new emerging magnetic flux along the neutral line of the old bipolar group led to the formation of a compact quadrupolar sunspot group, with strong twisting of penumbral filaments.