Bipolar Ephemeral Active Regions, Magnetic Flux Cancellation, and Solar Magnetic Explosions

TL;DR

This study investigates the magnetic evolution of bipolar ephemeral active regions in solar coronal holes, revealing that microflares are magnetic explosions associated with flux cancellation, resembling larger solar flares and CMEs.

Contribution

It provides detailed observational evidence linking flux cancellation to microflare explosions in bipolar ephemeral active regions, highlighting their similarities to larger solar eruptions.

Findings

Microflares are magnetic explosions occurring at polarity inversion lines.

Flux cancellation is evident before and during microflares.

Blowout explosions resemble miniature CMEs, with no inside-loop eruptions during emergence.

Abstract

We examine the cradle-to-grave magnetic evolution of 10 bipolar ephemeral active regions (BEARs) in solar coronal holes, especially aspects of the magnetic evolution leading to each of 43 obvious microflare events. The data are from Solar Dynamics Observatory: 211 A coronal EUV images and line-of-sight photospheric magnetograms. We find evidence that (1) each microflare event is a magnetic explosion that results in a miniature flare arcade astride the polarity inversion line (PIL) of the explosive lobe of the BEARs anemone magnetic field; (2) relative to the BEAR's emerged flux-rope omega loop, the anemone's explosive lobe can be an inside lobe, an outside lobe, or an inside & outside lobe; (3) 5 events are confined explosions, 20 events are mostly-confined explosions, and 18 events are blowout explosions, which are miniatures of the magnetic explosions that make coronal mass ejections (CMEs); (4) contrary to the expectation of Moore et al (2010), none of the 18 blowout events explode from inside the BEARs omega loop during the omega loops emergence; (5) before and during each of the 43 microflare events there is magnetic flux cancellation at the PIL of the anemone's explosive lobe. From finding evident flux cancellation at the underlying PIL before and during all 43 microflare events - together with BEARs evidently being miniatures of all larger solar bipolar active regions - we expect that in essentially the same way, flux cancellation in sunspot active regions prepares and triggers the magnetic explosions for many major flares and CMEs.