Why Is the Great Solar Active Region 12192 Flare-Rich But CME-Poor?

TL;DR

Despite producing numerous flares, active region 12192 remained CME-poor due to its weaker non-potential magnetic fields and stronger overlying fields, indicating that magnetic configuration limits eruptiveness.

Contribution

This study reveals that magnetic field conditions, particularly the ratio of non-potentiality to overlying field, explain why some active regions produce flares without CMEs, challenging previous assumptions.

Findings

AR 12192 had weaker non-potentiality than CME-productive regions.

Large magnetic free energy did not lead to CMEs in AR 12192.

Confined flares leave weaker photospheric and coronal imprints.

Abstract

Solar active region (AR) 12192 of October 2014 hosts the largest sunspot group in 24 years. It is the most prolific flaring site of Cycle 24, but surprisingly produced no coronal mass ejection (CME) from the core region during its disk passage. Here, we study the magnetic conditions that prevented eruption and the consequences that ensued. We find AR 12192 to be "big but mild"; its core region exhibits weaker non-potentiality, stronger overlying field, and smaller flare-related field changes compared to two other major flare-CME-productive ARs (11429 and 11158). These differences are present in the intensive-type indices (e.g., means) but generally not the extensive ones (e.g., totals). AR 12192's large amount of magnetic free energy does not translate into CME productivity. The unexpected behavior suggests that AR eruptiveness is limited by some relative measure of magnetic non-potentiality over the restriction of background field, and that confined flares may leave weaker photospheric and coronal imprints compared to their eruptive counterparts.