Observations of Turbulent Magnetic Reconnection within a Solar Current Sheet

Abstract

Magnetic reconnection is a fundamental physical process in various astrophysical, space, and laboratory environments. Many pieces of evidence for magnetic reconnection have been uncovered. However, its specific processes that could be fragmented and turbulent have been short of direct observational evidence. Here, we present observations of a super-hot current sheet during SOL2017-09-10T X8.2-class solar flare that display the fragmented and turbulent nature of magnetic reconnection. As bilateral plasmas converge toward the current sheet, significant plasma heating and non-thermal motions are detected therein. Two oppositely directed outflow jets are intermittently expelled out of the fragmenting current sheet, whose intensity shows a power-law distribution in spatial frequency domain. The intensity and velocity of the sunward outflow jets also display a power-law distribution in temporal frequency domain. The length-to-width ratio of the current sheet is estimated to be larger than theoretical threshold of and thus ensures occurrence of tearing mode instability. The observations therefore suggest fragmented and turbulent magnetic reconnection occurring in the long stretching current sheet.

Onset of Turbulent Fast Magnetic Reconnection Observed in the Solar Atmosphere

“…Previous suggestions of turbulence as a trigger process in solar flares and eruptions, based on lower spatiotemporal resolution observations, remained inconclusive (Ciaravella & Raymond 2008;Harra et al 2013). Fragmented current sheets and intermittent jets are investigated in a recent study, suggesting further the turbulent nature of magnetic reconnection (Cheng et al 2018). Through high-cadence IRIS observations, we quantitatively demonstrated the development and persistence of high-velocity transonic turbulence, turbulent broadening of the loop, and the subsequent microflare activity in the same feature, thus establishing the direct role of turbulence in triggering fast reconnection.…”

Spectropolarimetric Insight into Plasma Sheet Dynamics of a Solar Flare

“…The broad lines were hypothesized to indicate small-scale turbulent velocity fluctuations from plasmoid fragmentation during reconnection. In support of this idea, Cheng et al (2018) analyzed the plasma-sheet plane-of-sky (POS) outflows and find a power-law spectrum of fluctuations in wavenumber space consistent with a turbulent cascade of energy toward smaller scales.…”

“…Perhaps the brightest and longest-lived plasma-sheet observation to date is associated with an X8.2-class flare on September 10th 2017 (e.g. Long et al 2018;Warren et al 2018;Kuridze et al 2019;Li et al 2018, Cheng et al 2018Longcope et al 2018;Gary et al 2018;Morosan et al 2019). The flare and coronal mass ejection erupted from AR 12673 on the western solar limb, observed across the spectrum by multiple spacebased and ground-based instruments.…”

“…Therefore, if ℓ is greater than the observed plasma-sheet width w ≈ 5 Mm, n e < 1.4 × 10 10 cm −3 . Assuming ℓ ≈ 30 Mm (Cheng et al 2018), n e ≈ 2 × 10 9 cm −3 . These densities are not high enough to destroy atomic polarization via collisions.…”

Two Quasi-periodic Fast-propagating Magnetosonic Wave Events Observed in Active Region NOAA 11167

“…Magnetohydrodynamic (MHD) waves carry the vital information of the source region, they propagate across structured waveguides, therefore, the analysis of MHD waves could be used to infer the key parameters of both the source and waveguide on the sun, which are not usually measurable in practice. Various types of them have been detected and studied during the last decades, such as coronal extreme-ultraviolet (EUV) waves (e.g., Thompson et al 1998Thompson et al , 1999Liu et al 2010;Warmuth 2010;Warmuth & Mann 2011;Yuan & Nakariakov 2012;Yang et al 2013;Liu & Ofman 2014;Muhr et al 2014;Warmuth 2015;Goddard et al 2016;Kumar et al 2017;Pascoe et al 2017;Shen et al 2018b;Cheng et al 2018;Shen et al 2019;Goddard et al 2019;Pascoe et al 2019), chromospheric Moreton waves (Moreton 1960;Krause et al 2018;Chen & Wu 2011), fast mode (Ofman & Thompson 2002;Liu et al 2011Liu et al , 2012Yuan et al 2013;Zhang et al 2015;Ofman & Liu 2018) and slow mode (e.g., Nakariakov & Zimovets 2011;Yuan et al 2015b) magnetosonic waves. There are various types of waves that can lead to coronal loop and filament oscillations (Nakariakov & Ofman 2001;Nakariakov & Verwichte 2005;Chen et al 2008;Liu et al 2012;Shen et al 2014a,b;Zhou et al 2018).…”