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Triggering an eruptive flare by emerging flux in a solar active-region complex  

Rohan Eugene Louis   Submitted: 2015-06-29 05:43

A flare and fast coronal mass ejection originated between solar active regions NOAA 11514 and 11515 on July 1, 2012 in response to flux emergence in front of the leading sunspot of the trailing region 11515. Analyzing the evolution of the photospheric magnetic flux and the coronal structure, we find that the flux emergence triggered the eruption by interaction with overlying flux in a non-standard way. The new flux neither had the opposite orientation nor a location near the polarity inversion line, which are favorable for strong reconnection with the arcade flux under which it emerged. Moreover, its flux content remained significantly smaller than that of the arcade (approximately 40 %). However, a loop system rooted in the trailing active region ran in part under the arcade between the active regions, passing over the site of flux emergence. The reconnection with the emerging flux, leading to a series of jet emissions into the loop system, caused a strong but confined rise of the loop system. This lifted the arcade between the two active regions, weakening its downward tension force and thus destabilizing the considerably sheared flux under the arcade. The complex event was also associated with supporting precursor activity in an enhanced network near the active regions, acting on the large-scale overlying flux, and with two simultaneous confined flares within the active regions.

Authors: Louis, Rohan E.; Kliem, Bernhard; Ravindra, B.; Chintzoglou, Georgios
Projects: GOES X-rays ,GONG,SDO-AIA,SDO-HMI,SoHO-LASCO,STEREO

Publication Status: Accepted for publication in the Topical Issue of Solar Physics : Solar and Stellar Flares
Last Modified: 2015-06-29 11:54
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Sunspot splitting triggering an eruptive flare  

Rohan Eugene Louis   Submitted: 2013-11-22 03:29

We investigate how the splitting of the leading sunspot and associated flux emergence and cancellation in active region NOAA 11515 caused an eruptive M5.6 flare on 2012 July 2. Our study employs multi-wavelength observations from HMI, AIA and ChroTel. Emerging flux formed a neutral line ahead of the leading sunspot and new satellite spots. The sunspot splitting caused a long-lasting flow toward this neutral line, where a filament formed. Further flux emergence, partly of mixed-polarity, as well as episodes of flux cancellation occurred repeatedly at the neutral line. Following a nearby C-class precursor flare with signs of interaction with the filament, the filament erupted nearly simultaneously with the onset of the M5.6 flare and evolved into a coronal mass ejection. The sunspot stretched without forming a light bridge, splitting unusually fast (within about a day, complete approximately 6 hours after the eruption) in two nearly equal parts. The front part separated strongly from the active region to approach the neighbouring active region where all its coronal magnetic connections were rooted. It also rotated rapidly (by 4.9 degree/hr) and caused significant shear flows at its edge. The eruption resulted from a complex sequence of processes in the (sub-)photosphere and corona. The persistent flows toward the neutral line likely caused the formation of a flux rope which held the filament. These flows and their associated flux cancellation, the emerging flux, and the precursor flare all contributed to the destabilization of the flux rope. We interpret the sunspot splitting as the separation of two flux bundles differently rooted in the convection zone and only temporarily joined in the spot. This explains the rotation as continued rise of the separating flux and implies that at least this part of the sunspot was still connected to its roots deep in the convection zone.

Authors: Rohan E. Louis, Klaus G. Puschmann, Bernhard Kliem, Horst Balthasar, Carsten Denker
Projects: None

Publication Status: Accepted for publication in A&A
Last Modified: 2013-11-22 09:03
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Triggering an eruptive flare by emerging flux in a solar active-region complex
Sunspot splitting triggering an eruptive flare

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