Editing Coronal mass ejection (section)

====Initiation====
CME initiation occurs when a pre-eruption structure in an equilibrium state enters a nonequilibrium or [[metastable]] state where energy can be released to drive an eruption. The specific processes involved in CME initiation are debated, and various models have been proposed to explain this phenomenon based on physical speculation. Furthermore, different CMEs may be initiated by different processes.<ref name="howard11" />{{rp|175}}<ref name="vial15" />{{rp|303}}

It is unknown whether a magnetic flux rope exists prior to initiation, in which case either [[Magnetohydrodynamics#Ideal MHD|ideal]] or non-ideal magnetohydrodynamic (MHD) processes drive the expulsion of this flux rope, or whether a flux rope is created during the eruption by non-ideal process.<ref>{{cite journal |last1=Chen |first1=Bin |last2=Bastian |first2=T. S. |last3=Gary |first3=D. E. |title=Direct Evidence of an Eruptive, Filament-Hosting Magnetic Flux Rope Leading to a Fast Solar Coronal Mass Ejection |journal=The Astrophysical Journal |date=6 October 2014 |volume=794 |issue=2 |page=149 |doi=10.1088/0004-637X/794/2/149 |arxiv=1408.6473 |bibcode=2014ApJ...794..149C |s2cid=119207956 |url=https://iopscience.iop.org/article/10.1088/0004-637X/794/2/149/meta}}</ref><ref name="aschwanden19" />{{rp|555}} Under ideal MHD, initiation may involve ideal instabilities or [[Catastrophe theory|catastrophic]] loss of equilibrium along an existing flux rope:<ref name="chen11">{{cite journal |last1=Chen |first1=P. F. |title=Coronal Mass Ejections: Models and Their Observational Basis |journal=Living Reviews in Solar Physics |date=2011 |volume=8 |issue=1 |page=1 |doi=10.12942/lrsp-2011-1 |bibcode=2011LRSP....8....1C |s2cid=119386112 |doi-access=free }}</ref>
* The '''kink instability''' occurs when a magnetic flux rope is twisted to a critical point, whereupon the flux rope is unstable to further twisting.
* The '''torus instability''' occurs when the magnetic field strength of an arcade overlying a flux rope decreases rapidly with height. When this decrease is sufficiently rapid, the flux rope is unstable to further expansion.<ref>{{cite journal |last1=Titov |first1=V. S. |last2=Démoulin |first2=P. |title=Basic topology of twisted magnetic configurations in solar flares |journal=Astronomy and Astrophysics |date=October 1999 |volume=351 |issue=2 |pages=707–720 |bibcode=1999A&A...351..707T |url=https://www.researchgate.net/publication/234530273}}</ref>
* The '''catastrophe model'''  involves a catastrophic loss of equilibrium.
Under non-ideal MHD, initiations mechanisms may involve resistive instabilities or [[magnetic reconnection]]:
* '''Tether-cutting''', or '''flux cancellation''', occurs in strongly sheared arcades when nearly antiparallel field lines on opposite sides of the arcade form a current sheet and reconnect with each other. This can form a helical flux rope or cause a flux rope already present to grow and its axis to rise.
* The '''magnetic breakout model''' consists of an initial quadrupolar [[magnetic topology]] with a null point above a central flux system. As shearing motions cause this central flux system to rise, the null point forms a current sheet and the core flux system reconnects with the overlying magnetic field.<ref name="aschwanden19">{{cite book |last1=Aschwanden |first1=Markus J. |title=New Millennium Solar Physics |series=Astrophysics and Space Science Library |date=2019 |volume=458 |location=Cham, Switzerland | publisher=Springer International Publishing |doi=10.1007/978-3-030-13956-8 |isbn=978-3-030-13956-8 |s2cid=181739975 }}</ref>

[[File:Close-up on launching filament (SDO-AIA, 304 Å).ogv|thumb|Video of a [[solar prominence|solar filament]] being launched]]