Physics
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009spd....40.1905m&link_type=abstract
American Astronomical Society, SPD meeting #40, #19.05; Bulletin of the American Astronomical Society, Vol. 41, p.847
Physics
Scientific paper
Two whole-active-region magnetic quantities that can be measured from a line-of-sight magnetogram are LWLSG, a gauge of the total free energy in an active region's magnetic field, and LΦ, a measure of the active region's total magnetic flux. From these two quantities measured from 1865 SOHO/MDI magnetograms that tracked 44 sunspot active regions across the 0.5 RSun central disk, together with each active region's observed production of CMEs, X flares, and M flares, Falconer et al (2009, ApJ, submitted) found that (1) active regions have a maximum attainable free magnetic energy that increases with the magnetic size LΦ of the active region, (2) in (Log LWLSG, Log LΦ) space, CME/flare-productive active regions are concentrated in a straight-line main sequence along which the free magnetic energy is near its upper limit, and (3) X and M flares are restricted to large active regions. Here, from (a) these results, (b) the observation that even the greatest X flares produce at most only subtle changes in active-region magnetograms, and (c) measurements from MSFC vector magnetograms and from MDI line-of-sight magnetograms showing that practically all sunspot active regions have nearly the same area-averaged magnetic field strength: áBñ ≡ ΦA ≈ 300 G, where Φ is the active region's total photospheric flux of field stronger than 100 G and A is the area of that flux, we infer that (1) the maximum allowed ratio of an active region's free magnetic energy to its potential-field energy is 1, and (2) any one CME/flare eruption releases no more than a small fraction (< 10%) of the active region's free magnetic energy.
This work was funded by NASA's Heliophysics Division, NSF's Division of Atmospheric Sciences, and AFOSR's MURI Program.
Falconer David Allen
Moore Ronald L.
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