On the origin of the eruptive events of February 2011: Magnetic field evolution and low corona structure

LÓPEZ, FERNANDO M.; CRISTIANI, G.D.; FRANCILE, C.N.; MANDRINI, C.H.; GUTIÉRREZ ESCATE, M.V.; CREMADES, H.

Conferencia; XI Conferencia Latinoamericana de Geofísica Espacial (XI COLAGE); 2018

Active region(AR) NOAA 11158 produced several flares from 13 to 16 February 2011 accompaniedby coronal mass ejections (CMEs) and subsequent EUV waves. AR 11158 was formedby two main bipoles that emerged almost simultaneously and a few minor ones,observed in vector magnetograms obtained with the Helioseismic and MagneticImager onboard the Solar Dynamics Observatory.Flares and CMEsoriginated and evolved along different portions of the photospheric inversionline (PIL) following the displacement of the main bipoles, their sustainedrotation, and the built up of intense magnetic shear along the PILs wheretwisted flux ropes formed.  We model the coronalmagnetic field of the AR along the three days and study its topology. We findthe presence of a persistent magnetic null point, whose height and locationchanged as the photospheric field evolved. We propose that magenticreconnection occurring at the null neighborhood, forced by the photosphericmotions, could decrease the magnetic tension above the flux ropes giving  their repeated eruptions.