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We follow two small, magnetically isolated CME-producing solar active regions(ARs) from the time of their emergence until several days later, when theircore regions erupt to produce the CMEs. In both cases, magnetograms show: (a)following an initial period where the poles of the emerging regions separatefrom each other, the poles then reverse direction and start to retract inward;(b) during the retraction period, flux cancelation occurs along the mainneutral line of the regions; (c) this cancelation builds the sheared corefield/flux rope that eventually erupts to make the CME. In the two cases,respectively 30% and 50% of the maximum flux of the region cancels prior to theeruption. Recent studies indicate that solar coronal jets frequently resultfrom small-scale filaments eruptions, with those "minifilament" eruptions alsobeing built up and triggered by cancelation of magnetic flux. Together, thesmall-AR eruptions here and the coronal jet results suggest that isolatedbipolar regions tend to erupt when some threshold fraction, perhaps in therange of 50%, of the region's maximum flux has canceled. Our observed eruptingfilaments/flux ropes form at sites of flux cancelation, in agreement withprevious observations. Thus, the recent finding that minifilaments that eruptto form jets also form via flux cancelation is further evidence thatminifilaments are small-scale versions of the long-studied full-sizedfilaments.

Magnetic Flux Cancelation as the Buildup and Trigger Mechanism for CME-Producing Eruptions in two Small Active Regions