Observations of the Formation, Development, and Structure of a Current Sheet in an Eruptive Solar Flare

Abstract

We present Atmospheric Imaging Assembly observations of a structure we interpret as a current sheet associated with an X4.9 flare and coronal mass ejection that occurred on 2014February25 in NOAA Active Region 11990. We characterize the properties of the current sheet, finding that the sheet remains on the order of a few thousand kilometers thick for much of the duration of the event and that its temperature generally ranged between 8 and 10 MK. We also note the presence of other phenomena believed to be associated with magnetic reconnection in current sheets, including supra-arcade downflows and shrinking loops. We estimate that the rate of reconnection during the event was M A ≈0.004-0.007, a value consistent with model predictions. We conclude with a discussion of the implications of this event for reconnection-based eruption models.

Observations of Turbulent Magnetic Reconnection within a Solar Current Sheet

“…The apparent width of the current sheet is ∼25 Mm, and the lower limit of the apparent length is 400 Mm (Figure 4b). It corresponds to a maximal reconnection rate of ∼0.06, which, similar to the previous estimations (Savage et al 2010;Ling et al 2014;Seaton et al 2017), is still smaller than the maximum value derived above. In fact, the original current sheet could be fragmented into magnetic islands due to tearing mode instability.…”

“…Observations with a continuous field of view from 1 to 30 R and multiwavelengths including the white-light, EUV, and X-rays enable us to reveal the origin of and specific processes involved in magnetic reconnection. We successfully detect almost all ingredients predicted by models during a single eruption including the erupting hot flux rope, super-hot current sheet, cusp-shaped flare loops, inflows, and high-speed sunward and anti-sunward outflow jets, some of which have been detected in previous observations (Savage et al 2010;Ling et al 2014;Seaton et al 2017;Yan et al 2018;Liu et al 2018). The high temperature of the flux rope envelope and the cusp-shaped flare loops probably originates from the collision of the outflow jets with the local dense plasma and/or the direct heating by slow-mode shocks at both ends of the current sheet ).…”

Origin and structures of solar eruptions I: Magnetic flux rope

“…In the acceleration phase, as expected by the standard CME/flare model (Carmichael 1964;Sturrock 1966;Hirayama 1974;Kopp & Pneuman 1976), the eruption stretches the overlying magnetic fields, forming a CS in the wake of the erupting MFR (e.g., Lin et al 2005Lin et al , 2007Ciaravella & Raymond 2008;Cheng et al 2011b;Li et al 2016a;Zhu et al 2016;Seaton et al 2017). The reconnection in the CS efficiently injects poloidal fluxes to the MFR and thus accelerates its eruption.…”

Spectroscopic Observations of Current Sheet Formation and Evolution

“…Schettino et al (2010) and Ciaravella & Raymond (2008) report strong broadening in the Fe XVIII line. Seaton et al (2017) used AIA observations of a flare to infer temperatures in a current sheet and also find evidence for high temperature emis-sion. They do find much broader temperature distributions that peak at somewhat lower temperatures than we find, but their current sheet is relatively faint and they lacked spectroscopic data, so their inversions are not as well constrained.…”

“…Some spectroscopic observations from EIS near the base of the current sheet have been reported by Hara et al (2008). The properties of the current sheet have also been studied using imaging observations (e.g., Savage et al 2010;Seaton et al 2017;Zhu et al 2016). Our results are generally consistent with these previous studies and we will discuss this in detail in the final section of the paper.…”