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Resolving the Fan-Spine Reconnection Geometry of a Small-Scale Chromospheric Jet Event with the New Solar Telescope  

Zhicheng Zeng   Submitted: 2016-02-22 20:10

Jets present ubiquitously in both quiet and active regions on the Sun. They are widely believed to be driven by magnetic reconnection. A fan-spine structure has been frequently reported in some coronal jets and flares, regarded as a signature of ongoing magnetic reconnection in a topology consisting of a magnetic null connected by a fan-like separatrix surface and a spine. However, for small-scale chromospheric jets, clear evidence of such structures is rather rare, although they are implied in earlier works that show an inverted-Y-shaped feature. Here we report high-resolution (0".16) observations of a small-scale chromospheric jet obtained by the New Solar Telescope (NST) using 10830 Å filtergrams. Bi-directional flows were observed across the separatrix regions in the 10830 Å images, suggesting that the jet was produced due to magnetic reconnection. At the base of the jet, a fan-spine structure was clearly resolved by the NST, including the spine and the fan-like surface, as well as the loops before and after the reconnection. A major part of this fan-spine structure, with the exception of its bright footpoints and part of the base arc, was invisible in the extreme ultraviolet and soft X-ray images (observed by the Atmosphere Imaging Assembly and the X-Ray Telescope, respectively), indicating that the reconnection occurred in the upper chromosphere. Our observations suggest that the evolution of this chromospheric jet is consistent with a two-step reconnection scenario proposed by Torok2009

Authors: Zhicheng Zeng, Bin Chen, Haisheng Ji, Philip R. Goode, Wenda Cao
Projects: None

Publication Status: ApJ, 819, L3
Last Modified: 2016-02-22 20:42
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A Flare Observed in Coronal, Transition Region and Helium I 10830 Å Emissions  

Zhicheng Zeng   Submitted: 2014-08-04 09:36

On June 17, 2012, we observed the evolution of a C-class flare associated with the eruption of a filament near a large sunspot in the active region NOAA 11504. We obtained high spatial resolution filtergrams using the 1.6 m New Solar Telescope at the Big Bear Solar Observatory in broad-band TiO at 706 nm (bandpass:10 ?) and He I 10830 Å narrow-band (bandpass: 0.5 ?, centered 0.25 ? to the blue). We analyze the spatio-temporal behavior of the He I 10830 Å data, which were obtained over a 90" X 90" field of view with a cadence of 10 sec. We also analyze simultaneous data from the Atmospheric Imaging Assembly and Extreme Ultraviolet Variability Experiment instruments on board the Solar Dynamics Observatory spacecraft, and data from Reuven Ramaty High Energy Solar Spectroscopic Imager and GOES spacecrafts. Non-thermal effects are ignored in this analysis. Several quantitative aspects of the data, as well as models derived using the "0D" Enthalpy-Based Thermal Evolution of Loops model (EBTEL: Klimchuk et al. 2008) code, indicate that the triplet states of the 10830 Å multiplet are populated by photoionization of chromospheric plasma followed by radiative recombination. Surprisingly, the He II 304 Å line is reasonably well matched by standard emission measure calculations, along with the C IV emission which dominates the AIA 1600 Å channel during flares. This work lends support to some of our previous work combining X-ray, EUV and UV data of flares to build models of energy transport from corona to chromosphere.

Authors: Zhicheng Zeng, Jiong Qiu, Wenda Cao, Philip G. Judge
Projects: None

Publication Status: Accepted
Last Modified: 2014-08-04 17:58
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Resolving the Fan-Spine Reconnection Geometry of a Small-Scale Chromospheric Jet Event with the New Solar Telescope
A Flare Observed in Coronal, Transition Region and Helium I 10830 ? Emissions

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