Physics
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011spd....42.2305m&link_type=abstract
American Astronomical Society, SPD meeting #42, #23.05; Bulletin of the American Astronomical Society, Vol. 43, 2011
Physics
Scientific paper
From measurement of magnetic flux and a proxy of free magnetic energy from 1800 SOHO/MDI line-of-sight magnetograms of 44 sunspot active regions, Falconer et al (2009, ApJ, 700, L169) showed (1) there is an upper limit to the free magnetic energy an active region can hold, (2) this limit increases with active-region magnetic size (flux content), (3) most major CME/flare eruptions are produce by active regions that are near their free-energy limit, (4) in (flux content, free-energy proxy) phase space, the source active regions for major CME/flare eruptions are concentrated along a main sequence, a path that runs close below the free-energy limit line, and (5) the free-energy limit and the main sequence probably result from the steep increase in CME/flare productivity as an active region approaches its free-energy limit, depleting the active region's free energy as fast as it is built up. Here we present (1) a new direct proxy of an active region's free magnetic energy, and (2) a corresponding proxy of the ratio of free energy to potential-field energy in the more-nonpotential parts of the active region. Each is measured from a vector magnetogram of the active region. From these two magnetic-energy proxies measured from Marshall Space Flight Center vector magnetograms of 42 of the active regions of Falconer et al (2009), we (1) affirm that the free-energy proxy measured in Falconer et al (2009) is indeed a proxy of an active region's free magnetic energy, (2) further support the above reason for the main sequence of explosive active regions, and (3) conclude that magnetic fields in active regions become ready to explode and produce CME/flare eruptions when their free energy becomes comparable to the potiential-field energy.
This work was supported by funding from 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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