Dynamical and Physical Properties of a Post–Coronal Mass Ejection Current Sheet

Abstract

In the eruptive process of the Kopp-Pneuman type, the closed magnetic field is stretched by the eruption so much that it is usually believed to be '' open '' to infinity. Formation of the current sheet in such a configuration makes it possible for the energy in the coronal magnetic field to quickly convert into thermal and kinetic energies and cause significant observational consequences, such as growing postflare/CME loop system in the corona, separating bright flare ribbons in the chromosphere, and fast ejections of the plasma and the magnetic flux. An eruption on 2002 January 8 provides us a good opportunity to look into these observational signatures of and place constraints on the theories of eruptions. The event started with the expansion of a magnetic arcade over an active region, developed into a coronal mass ejection (CME), and left some thin streamer-like structures with successively growing loop systems beneath them. The plasma outflow and the highly ionized states of the plasma inside these streamer-like structures, as well as the growing loops beneath them, lead us to conclude that these structures are associated with a magnetic reconnection site, namely, the current sheet, of this eruptive process. We combine the data from the Ultraviolet Coronagraph Spectrometer, Large Angle and Spectrometric Coronagraph Experiment, EUV Imaging Telescope, and Coronal Diagnostic Spectrometer on board the Solar and Heliospheric Observatory, as well as from the Mauna Loa Solar Observatory Mark IV K-coronameter, to investigate the morphological and dynamical properties of this event, as well as the physical properties of the current sheet. The velocity and acceleration of the CME reached up to 1800 km s À1 and 1 km s À2 , respectively. The acceleration is found to occur mainly at the lower corona (<2.76 R ). The post-CME loop systems showed behaviors of both postflare loops (upward motion with decreasing speed) and soft X-ray giant arches (upward motion with constant speed, or acceleration) according to the definition of Š vestka. In the current sheet, the presence of highly ionized ions, such as Fe +17 and Ca +13 , suggests temperature as high as ð3 4Þ Â 10 6 K, and the plasma outflows have speeds ranging from 300 to 650 km s À1 . Absolute elemental abundances in the current sheet show a strong first ionization potential effect and have values similar to those found in the active region streamers. The magnetic field strength in the vicinity of the current sheet is found to be of the order of 1 G.

Review on Current Sheets in CME Development: Theories and Observations

“…Different mechanisms could give rise to the same output. For example, Sweet-Parker CS with anomalous resistivity Biskamp 2000;Priest and Forbes 2000), Petschek-type reconnection (Petschek 1964;Biskamp 1986;Forbes and Priest 1987;Yokoyama and Shibata 1994;Kulsrud 2001;Drake et al 2006;Baty et al 2009;Vršnak et al 2009;Zweibel and Yamada 2009;Ko et al 2010;Liu et al 2012), and turbulent reconnection (Strauss 1988;Bhattacharjee and Yuan 1995;Lazarian and Vishniac 1999;Lin et al 2007Lin et al , 2009Lazarian et al , 2014. These different dissipation styles may even work together to yield a much more complex pattern and more efficient diffusion than that dominated only by a single mechanism (e.g., see also Mei et al 2012).…”

“…Several early versions of the two-ribbon flare configuration could be found in the work of Švestka and Cliver (1992). It is now known that the motions of the flare ribbons and loops are not due to mass motions of the plasma but rather due to the upward propagation of the energy source onto new magnetic field lines at higher altitudes (Schmieder et al 1987); the hot X-ray loops are the newly reconnected closed loops, located at the outermost edge of the loop system, mapping to the outer edge of the flare ribbons; while the cool Hα loops are formed from the hot ones by conductive and radiative cooling (see Ko et al 2003 and references therein for a brief review on this issue). (Note: The term "altitude" used in this paper means the distance measured from the surface of the Sun.…”

Magnetic Reconnection Inflow near the CME/Flare Current Sheet

“…Following Ciaravella et al (2002), Ko et al (2003) and Webb et al (2003), the current sheet developing in the wake of a CME is investigated once again. The event discussed here occurred on the east limb of the Sun on November 18, 2003.…”

“…Utilizing the ultraviolet spectroscopic observations from the Ultraviolet Coronagraphic Spectrometer (UVCS) on board the Solar and Heliospheric Observatory (SOHO), together with other remote-sensing data, Ciaravella et al (2002) and Ko et al (2003) conducted comprehensive analyses from various aspects on several eruptive processes that clearly manifested both coronal mass ejections (CMEs) and solar flares, and confirmed the existence and development of the long current sheet in the events as predicted by Lin & Forbes (2000). Webb et al (2003) surveyed 59 CMEs observed by the Solar Maximum Mission from 1984 to 1989, and found that about half were followed by co-axial, bright rays suggestive of newly formed current sheets.…”

“…This makes direct observation of the current sheet extremely difficult (refer to Ko et al 2003 for the discussions and brief review on this issue). Therefore, information about magnetic reconnection inside the current sheet is usually deduced indirectly by observing the dynamical behaviors of the products of magnetic reconnection, such as the separating flare ribbons on the solar surface (Poletto & Kopp 1986;Qiu et al 2004), the growing flare loops in the corona (Sui et al 2004), and so on.…”