Filament Activation in Response to Magnetic Flux Emergence and Cancellation in Filament Channels

TL;DR

This study compares two filament activation events caused by magnetic flux emergence, revealing that flux cancellation near filament barbs is a key trigger for filament eruptions, while large flux emergence alone may not destabilize filaments.

Contribution

It provides the first detailed observational comparison showing how flux emergence location influences filament stability and eruption, emphasizing the role of flux cancellation near barbs.

Findings

Flux emergence near barbs leads to filament eruption via flux cancellation.

Emergence of an entire active region does not necessarily destabilize a filament.

Flux cancellation near filament barbs is a critical factor for eruption.

Abstract

We make a comparative analysis for two filaments that showed quite different activation in response to the flux emergence within the filament channels. The observations from the Solar Dynamics Observatory (SDO) and Global Oscillation Network Group (GONG) are carried out to analyze the two filaments on 2013 August 17-20 and September 29. The first event showed that the main body of the filament was separated into two parts when an active region (AR) emerged with a maximum magnetic flux of about 6.4*10^21 Mx underlying the filament. The close neighborhood and common direction of the bright threads in the filament and the open AR fan loops suggest similar magnetic connectivity of these two flux systems. The equilibrium of the filament was not destroyed within 3 days after the start of the emergence of the AR. To our knowledge, similar observations have never been reported before. In the second event, the emerging flux occurred nearby a barb of the filament with a maximum magnetic flux of 4.2*10^20 Mx, about one order of magnitude less than that of the first event. The emerging flux drove the convergence of two patches of parasitic polarity in the vicinity of the barb, and resulted in cancellation between the parasitic polarity and nearby network fields. About 20 hours after the onset of the emergence, the filament was entirely erupted. Our findings imply that the location of emerging flux within the filament channel is probably crucial to filament evolution. If the flux emergence appears nearby the barbs, flux cancellation of emerging flux with the filament magnetic fields is prone to occur, which probably causes the filament eruption. The comparison of the two events shows that the emergence of an entire AR may still not be enough to disrupt the stability of a filament system and the actual eruption does occur only after the flux cancellation sets in.