The Main Sequence of Explosive Emerging Solar Active Regions

Astronomy and Astrophysics – Astronomy

Scientific paper

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Scientific paper

We study the dependence of production of major CME/flare eruptions on the source active region's (AR's) location in (flux content, free energy) phase space. For this, an AR's flux content and a proxy of its free magnetic energy content can be adequately measured from 96-minute cadence SOHO/MDI magnetograms when the AR is within 30 degrees of disk center (Falconer et al 2008, ApJ, 688, 143). The AR's evolution in this phase space can thereby be tracked as it crosses the central disk. By our definition, an AR is (1) mature if its flux is growing by less than 50%/day when it rotates onto the 30-degree-radius central disk, or (2) emerging if its flux is growing faster than 50%/day when it enters the central disk or if it is born within the central disk. In an initial study of 46 ARs, 42 were mature and 4 were emerging. From 1800 MDI magnetograms of the 42 mature ARs, we found that (1) mature ARs have a sharp upper bound on the free energy they can attain that increases with increasing flux content, and (2) for mature ARs, nearly all CMEs and X-class flares are produced by ARs that are near the free-energy limit line. These ARs constitute the main sequence of explosive mature ARs (Falconer et al 2009, ApJ, 700, L166). Two of the four emerging ARs attained free energy well beyond the limit for mature ARs of the same flux content, questioning whether emerging ARs have a free-energy limit and explosive main sequence like those for mature ARs. Here, we show from a much larger sample of ARs ( 1000), of which about 1/3 are emerging, that emerging ARs do have a free-energy limit and a explosive main sequence, each offset to higher free energy relative to its mature-AR counterpart.

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