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Bidirectional outflows as evidence of magnetic reconnection leading to a solar microflare  

Jie Hong   Submitted: 2016-03-03 18:23

Magnetic reconnection is a rapid energy release process that is believed to be responsible for flares on the Sun and stars. Nevertheless, such flare-related reconnection is mostly detected to occur in the corona, while there have been few studies concerning the reconnection in the chromosphere or photosphere. Here we present both spectroscopic and imaging observations of magnetic reconnection in the chromosphere leading to a microflare. During the flare peak time, chromospheric line profiles show significant blueshifted/redshifted components on the two sides of the flaring site, corresponding to upflows and downflows with velocities of ±(70-80) km s-1, comparable with the local Alfvén speed as expected by the reconnection in the chromosphere. The three-dimensional nonlinear force-free field configuration further discloses twisted field lines (a flux rope) at a low altitude, cospatial with the dark threads in He I 10830 Å images. The instability of the flux rope may initiate the flare-related reconnection. These observations provide clear evidence of magnetic reconnection in the chromosphere and show the similar mechanisms of a microflare to those of major flares.

Authors: Jie Hong, M. D. Ding, Ying Li, Kai Yang, Xin Cheng, Feng Chen, Cheng Fang, Wenda Cao
Projects: None

Publication Status: ApJL (accepted)
Last Modified: 2016-03-08 12:17
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Spectral observations of Ellerman bombs and fitting with a two-cloud model  

Jie Hong   Submitted: 2014-07-13 19:21

We study the Hα and Ca II 8542 Å line spectra of four typical Ellerman bombs (EBs) in active region NOAA 11765 on 2013 June 6, observed with the Fast Imaging Solar Spectrograph installed at the 1.6 meter New Solar Telescope at Big Bear Solar Observatory. Considering that EBs may occur in a restricted region in the lower atmosphere, and that their spectral lines show particular features, we propose a two-cloud model to fit the observed line profiles. The lower cloud can account for the wing emission, and the upper cloud is mainly responsible for the absorption at line center. After choosing carefully the free parameters, we get satisfactory fitting results. As expected, the lower cloud shows an increase of the source function, corresponding to a temperature increase of 400-1000 K in EBs relative to the quiet Sun. This is consistent with previous results deduced from semi-empirical models and confirms that a local heating occurs in the lower atmosphere during the appearance of EBs. We also find that the optical depths can increase to some extent in both the lower and upper clouds, which may result from either a direct heating in the lower cloud, or illumination by an enhanced radiation on the upper cloud. The velocities derived from this method, however, are different from those obtained using the traditional bisector method, implying that one should be cautious when interpreting this parameter. The two-cloud model can thus be used as an efficient method to deduce the basic physical parameters of EBs.

Authors: Jie Hong, M. D. Ding, Ying Li, Cheng Fang, Wenda Cao
Projects: None

Publication Status: ApJ accepted
Last Modified: 2014-07-16 12:57
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Bidirectional outflows as evidence of magnetic reconnection leading to a solar microflare
Spectral observations of Ellerman bombs and fitting with a two-cloud model

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