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The Torus instability
Bernhard Kliem,Tibor Torok +1 more
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In this paper, the expansion instability of a toroidal current ring in low-beta magnetized plasma is investigated, and the results are verified with experiments on spheromak expansion and with essential properties of solar coronal mass ejections.Abstract:
The expansion instability of a toroidal current ring in low-beta magnetized plasma is investigated. Qualitative agreement is obtained with experiments on spheromak expansion and with essential properties of solar coronal mass ejections, unifying the two apparently disparate classes of fast and slow coronal mass ejections.read more
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Photospheric Flux Cancellation and the Build-up of Sigmoidal Flux Ropes
Abstract: In this study we explore the scenario of photospheric flux cancellation being the primary formation mechanism of sigmoidal flux ropes in decaying active regions. We analyze magnetogram and X-ray observations together with data-driven non-linear force-free field (NLFFF) models of observed sigmoidal regions to test this idea. We measure the total and canceled fluxes in the regions from MDI magnetograms, as well as the axial and poloidal flux content of the modeled NLFFF flux ropes for three sigmoids—2007 February, 2007 December, and 2010 February. We infer that the sum of the poloidal and axial flux in the flux ropes for most models amounts to about 60%-70% of the canceled flux and 30%-50% of the total flux in the regions. The flux measurements and the analysis of the magnetic field structure show that the sigmoids first develop a strong axial field manifested as a sheared arcade and then, as flux cancellation proceeds, form long S-shaped field lines that contribute to the poloidal flux. In addition, the dips in the S-shaped field lines are located at the sites of flux cancellation that have been identified from the MDI magnetograms. We find that the line-of-sight-integrated free energy is also concentrated at these locations for all three regions, which can be liberated in the process of eruption. Flare-associated brightenings and flare loops coincide with the location of the X-line topology that develops at the site of most vigorous flux cancellation.
Journal ArticleDOI
Automatic detection and tracking of coronal mass ejections. II. Multiscale filtering of coronagraph images
TL;DR: In this paper, the authors present a new CORIMP (coronal image processing) CME detection and tracking technique, which overcomes many of the drawbacks of current catalogs.
Catastrophe versus instability for the eruption of a toroidal
TL;DR: In this paper, the onset of a solar eruption is formulated as either a magnetic catastrophe or as an instability, both starting with the same equation of force balance governing the underlying equilibria.
Journal ArticleDOI
Magnetic Helicity Estimations in Models and Observations of the Solar Magnetic Field. Part I: Finite Volume Methods
Gherardo Valori,Etienne Pariat,Sergey Anfinogentov,Feng Chen,Manolis K. Georgoulis,Yang Guo,Yang Liu,Kostas Moraitis,Julia K. Thalmann,Shangbin Yang +9 more
TL;DR: In this article, a comparison of six existing methods for the estimation of the helicity of magnetic fields known in a finite volume is presented, and compared with each other, and specifically tested for accuracy and sensitivity to errors.
Journal ArticleDOI
Flux-Rope Twist in Eruptive Flares and CMEs: Due to Zipper and Main-Phase Reconnection.
Eric Priest,Dana Longcope +1 more
TL;DR: In this paper, the nature of three-dimensional reconnection when a twisted flux tube erupts during an eruptive flare or coronal mass ejection is considered, and two phases are modeled in a simple way that assumes the initial magnetic flux is fragmented along the polarity inversion line.
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