Further Evidence for Magnetic Flux Cancelation as the Build-up and Trigger Mechanism for Eruptions in Isolated Solar Active Regions

We examine the magnetic evolution of three eruption-producing solar active regions (ARs), one each from 2013, 2014, and 2017, using data from SDO HMI and AIA. Each of the ARs is relatively small, so that we can follow its entire development during a single disk passage, from birth by emergence through the time of the respective eruptions; the first-, second-, and third-born respectively lived 3, 6.5, and 3 days before eruption. Each AR was relatively isolated, with minimal interaction with surrounding ARs, allowing us to study each AR as an approximately isolated system. CMEs resulted from eruptions in the first two ARs, while the third AR's eruption was smaller and appeared confined. In each AR, the eruption was seated on an interval of the AR's magnetic polarity inversion line (neutral line) where opposite-polarity flux was merging together and undergoing apparent cancelation. Our results, together with an earlier pilot study of two ARs by Sterling et al. (2018), and along with recent studies of solar coronal jets, support the view that the magnetic field that explodes to produce solar eruptions of size scales ranging from jets to CMEs are usually built and triggered by flux cancelation along a sharp neutral line.