경희대학교 BK21

 

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● 날짜 : 2016년 11월 08일 (화요일)
● 시간 : 16시 30분
● 장소 : 천문대 영상실
● 강사 : Prof. Brigitte Schmieder (Observatoire de Paris, LESIA)

 
Title : Flare and CMEs : triggering mechanisms
 
Abstract :
CMEs are due to physical phenomena that drive both, eruptions and flares in active regions. Eruptions/CMEs must be driven from an initially force-free current-carrying magnetic field. Sigmoids observed in X-rays, and UV, as well as the pattern (double J-shaped) of electric current in the photosphere show a clear evidence of currents parallel to the magnetic field and may be the signature of the existence of a flux rope which is detectable in CMEs. The magnetic helicity of filaments and active regions is an interesting measurable parameter because it can quantify the twist of the flux rope. On the other hand, the magnetic helicity of the solar structures allows us to associate solar eruptions and magnetic clouds in the heliosphere. The topology analysis using 3D magnetic field extrapolated from vector magnetograms is a good tool to show the reconnection sites (null points) and/or the 3D large volumes (hyperbolic flux tube-HFT) where reconnection can occur and release the energy. Flares are more associated to the presence of quasi-separatrix layers (QSLs) and HTF than to a single null point, which is a peculiar case. We review various mechanisms that have been proposed to trigger CMEs with their observable signatures: by breaking the field lines overlying the flux rope or by reconnection below the flux rope to reduce the magnetic tension, or by leaving the flux rope to expand until it reaches a minimum threshold height (loss of equilibrium or torus instability). Additional mechanisms are commonly operating in the solar atmosphere. Examples of observations will be presented all along the talk and discussed in this framework.