Signatures of Magnetic Reconnection at the Footpoints of Fan-shaped Jets on a Light Bridge Driven by Photospheric Convective Motions

Abstract

Dynamical jets are generally found on Light bridges (LBs), which are key to studying sunspots decays. So far, their formation mechanism is not fully understood. In this paper, we used state-of-the-art observations from the Goode Solar Telescope, the Interface Region Imaging Spectrograph, the Spectro-Polarimeter on board Hinode and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory to analyze the fan shape jets on LBs in detail. Continuous upward motion of the jets in ascending phase is found from the Hα velocity, which lasts for 12 minutes and is associated with the Hα line wing enhancements.Two mini jets appear upon the bright fronts of the fan shape jets visible in the AIA 171Å and 193Å channels, with a time interval as short as 1 minute. Two kinds of small scale convective motions are identified in the photospheric images, along with the Hα line wing enhancements. One seems to be associated with the formation of a new convection cell and the other manifests as the motion of a dark lane passing through the convection cell. The finding of three lobes Stokes V profiles and their inversion with NICOLE code indicates that there is magnetic field lines with opposite polarities in LBs. From the Hα -0.8Å images, we found ribbon like brightenings propagating along the LBs, possibly indicating slipping reconnection. Our observation supports that the fan shape jets under study are caused by the magnetic reconnection and photospheric convective motions play an important role in triggering the magnetic reconnection.

A New View of the Solar Interface Region from the Interface Region Imaging Spectrograph (IRIS)

“…Numerical simulations and IRIS and SDO observations have revealed the peculiar magnetic-field configuration in light bridges that leads to reconnection . IRIS observations have also elucidated the cross-field coherence in dynamic evolution of these lightwalls, which has been associated with slipping reconnection (Hou et al, 2016b;Bai et al, 2019): the light-wall dynamics appear to be intimately tied to, and thus help reveal the overall changes in, magnetic topology during a flare. High-resolution spatial and temporal data from IRIS and SDO have been used to confirm the observation of signatures of magnetic reconnection and accompanying flux cancelation (Yang et al, 2018b) including two-loop interaction processes, plasma blob ejections, and sheet-like structures above the flux-cancelation sites.…”

“…IRIS observations have been used to study their propagation and the evolution of non-linear harmonics as they travel upwards (Chae et al, 2018), as well as their frequency-dependent damping in sunspot umbrae (Krishna Prasad et al, 2017). Shock waves have also been studied (using coordinated data from DST or Hinode) in sunspot light bridges, with their provenance tied to magnetic reconnection and leakage of photospheric waves (Tian et al, 2018a;Bai et al, 2019). Similar processes have been invoked to explain the presence of high-frequency signals discovered in active-region plage (Narang et al, 2019).…”

“…Evidence of such emission was independently found in the IRIS Si IV lines by Nóbrega-Siverio et al (2017) and Guglielmino, Young, and Zuccarello (2019). Other examples of chromospheric ejections with associated TR emission observed with IRIS are fan-shaped jets originating from light bridges (Yang et al, 2015;Bharti, 2015;Bai et al, 2019) and penumbral microjets Humphries et al, 2020), although penumbral microjets are not genuine jets with significant mass motions, but rather manifestations of heat fronts (Esteban Buehler et al, 2019; Rouppe van der Voort and Drews, 2019; Drews and Rouppe van der Voort, 2020). In order to properly understand the TR emission of the aforementioned phenomena, one has to take the highly dynamic nature of the chromosphere into account as well as the fact that some elements in the TR have long ionization and recombination timescales, leading to relevant non-equilibrium ionization effects (e.g.…”

Sunspot penumbral filaments intruding into a light bridge and the resultant reconnection jets

“…The structures mentioned above are usually derived from local inhomogeneous magnetic field and magneto-convection, indicating the complexity of sunspot magnetic and thermal properties (Spruit & Scharmer 2006;Schüssler & Vögler 2006;Rimmele 2008;Rempel et al 2009;Reardon et al 2013). As a result of the deviation from sunspot background conditions, various dynamic phenomena especially surge-like activities frequently occur around these structures, such as surges and light walls above the light bridges (Roy 1973;Asai et al 2001;Shimizu et al 2009;Louis et al 2014a;Yang et al 2015Yang et al , 2016Yang et al , 2017Bharti 2015;Robustini et al 2016;Hou et al 2016aHou et al ,b, 2017Zhang et al 2017;Tian et al 2018;Bai et al 2019), transient jets above a penumbral filament intrusion into the umbra (Bharti et al 2017), and ubiquitous penumbral microjets in the penumbral chromosphere (Katsukawa et al 2007b;Jurčák & Katsukawa 2008;Nakamura et al 2012;Tiwari et al 2016;Drews & Rouppe van der Voort 2017;Samanta et al 2017;Esteban Pozuelo et al 2019; Rouppe van der Voort & Drews 2019). These surge-like activities display an impressive variety of morphological, temporal, and spectral properties.…”

Magnetic Reconnection in the Solar Corona

“…So far, their formation mechanism is not fully understood. Data observed by Goode Solar Telescope, IRIS, Spectro-polarimeter/Hinode and AIA/SDO enabled Bai et al (2019) to study the dynamical properties of fan-like light bridges. The Hα −0.8 Å images revealed the propagation of ribbon-like brightenings along the light bridges which they considered as evidence of slipping reconnection.…”