TY  - GEN
A1  - Green, Lucie M.
A1  - Kliem, Bernhard
T1  - Observations of flux rope formation prior to coronal mass ejections
T2  - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - Understanding the magnetic configuration of the source regions of coronal mass ejections (CMEs) is vital in order to determine the trigger and driver of these events. Observations of four CME productive active regions are presented here, which indicate that the pre-eruption magnetic configuration is that of a magnetic flux rope. The flux ropes are formed in the solar atmosphere by the process known as flux cancellation and are stable for several hours before the eruption. The observations also indicate that the magnetic structure that erupts is not the entire flux rope as initially formed, raising the question of whether the flux rope is able to undergo a partial eruption or whether it undergoes a transition in specific flux rope configuration shortly
before the CME.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 607 
KW  - Sun: coronal mass ejections (CMEs)
KW  - Sun: activity
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-416103
SN  - 1866-8372
IS  - 607
ER  - 
TY  - JOUR
A1  - Valori, Gherardo
A1  - Green, Lucie M.
A1  - Demoulin, P.
A1  - Vargas Dominguez, S.
A1  - van Driel-Gesztelyi, L.
A1  - Wallace, A.
A1  - Baker, Daniel N.
A1  - Fuhrmann, Marcel
T1  - Nonlinear force-free extrapolation of emerging flux with a global twist and serpentine fine structures
JF  - Solar physics : a journal for solar and solar-stellar research and the study of solar terrestrial physics
N2  - We study the flux emergence process in NOAA active region 11024, between 29 June and 7 July 2009, by means of multi-wavelength observations and nonlinear force-free extrapolation. The main aim is to extend previous investigations by combining, as much as possible, high spatial resolution observations to test our present understanding of small-scale (undulatory) flux emergence, whilst putting these small-scale events in the context of the global evolution of the active region. The combination of these techniques allows us to follow the whole process, from the first appearance of the bipolar axial field on the east limb, until the buoyancy instability could set in and raise the main body of the twisted flux tube through the photosphere, forming magnetic tongues and signatures of serpentine field, until the simplification of the magnetic structure into a main bipole by the time the active region reaches the west limb. At the crucial time of the main emergence phase high spatial resolution spectropolarimetric measurements of the photospheric field are employed to reconstruct the three-dimensional structure of the nonlinear force-free coronal field, which is then used to test the current understanding of flux emergence processes. In particular, knowledge of the coronal connectivity confirms the identity of the magnetic tongues as seen in their photospheric signatures, and it exemplifies how the twisted flux, which is emerging on small scales in the form of a sea-serpent, is subsequently rearranged by reconnection into the large-scale field of the active region. In this way, the multi-wavelength observations combined with a nonlinear force-free extrapolation provide a coherent picture of the emergence process of small-scale magnetic bipoles, which subsequently reconnect to form a large-scale structure in the corona.
KW  - Active regions, magnetic fields
KW  - Magnetic field, photosphere, corona
Y1  - 2012
U6  - https://doi.org/10.1007/s11207-011-9865-8
SN  - 0038-0938
VL  - 278
IS  - 1
SP  - 73
EP  - 97
PB  - Springer
CY  - Dordrecht
ER  - 
TY  - JOUR
A1  - Green, Lucie M.
A1  - Kliem, Bernhard
T1  - Flux rope formation preceding coronal mass ejection onset
N2  - We analyze the evolution of a sigmoidal (S-shaped) active region toward eruption, which includes a coronal mass ejection (CME) but leaves part of the filament in place. The X-ray sigmoid is found to trace out three different magnetic topologies in succession: a highly sheared arcade of coronal loops in its long-lived phase, a bald-patch separatrix surface (BPSS) in the hours before the CME, and the first flare loops in its major transient intensity enhancement. The coronal evolution is driven by photospheric changes which involve the convergence and cancellation of flux elements under the sigmoid and filament. The data yield unambiguous evidence for the existence of a BPSS, and hence a flux rope, in the corona prior to the onset of the CME.
Y1  - 2009
UR  - http://iopscience.iop.org/2041-8205
U6  - https://doi.org/10.1088/0004-637x/700/2/L83
SN  - 2041-8213
ER  -