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Observational Evidence of Magnetic Reconnection for Brightenings and Transition Region Arcades in IRIS observations  

Jie Zhao   Submitted: 2017-01-30 20:21

By using a new method of forced-field extrapolation, we study the emerging flux region AR 11850 observed by the Interface Region Imaging Spectrograph (IRIS) and Solar Dynamical Observatory (SDO). Our results suggest that the bright points (BPs) in this emerging region have responses in lines formed from the upper photosphere to the transition region, with a relatively similar morphology. They have an oscillation of several minutes according to the Atmospheric Imaging Assembly (AIA) data at 1600 and 1700 Å . The ratio between the BP intensities measured in 1600 Å and 1700 Å filtergrams reveals that these BPs are heated differently. Our analysis of the Helioseismic and Magnetic Imager (HMI) vector magnetic field and the corresponding topology in AR11850 indicates that the BPs are located at the polarity inversion line (PIL) and most of them related with magnetic reconnection or cancelation. The heating of the BPs might be different due to different magnetic topology. We find that the heating due to the magnetic cancelation would be stronger than the case of bald patch reconnection. The plasma density rather than the magnetic field strength could play a dominant role in this process. Based on physical conditions in the lower atmosphere, our forced-field extrapolation shows consistent results between the bright arcades visible in slit-jaw image (SJI) 1400 Å and the extrapolated field lines that pass through the bald patches. It provides a reliable observational evidence for testing the mechanism of magnetic reconnection for the BPs and arcades in emerging flux region, as proposed in simulation works.

Authors: Jie Zhao, Brigitte Schmieder, Hui Li, Etienne Pariat, Xiaoshuai Zhu, Li Feng, Michalina Grubecka

Publication Status: Accepted by ApJ. In Press.
Last Modified: 2017-01-31 11:46
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Hooked flare ribbons and flux-rope related QSL footprints  

Jie Zhao   Submitted: 2016-03-28 01:17

We studied the magnetic topology of active region 12158 on 2014 September 10 and compared it with the observations before and early in the flare which begins at 17:21 UT (SOL2014-09-10T17:45:00). Our results show that the sigmoidal structure and flare ribbons of this active region observed by SDO/AIA can be well reproduced from a Grad-Rubin non linear force free field extrapolation method. Various inverse-S and -J shaped magnetic field lines, that surround a coronal flux rope, coincide with the sigmoid as observed in different extreme ultraviolet wavelengths, including its multi-threaded curved ends. Also, the observed distribution of surface currents in the magnetic polarity where it was not prescribed is well reproduced. This validates our numerical implementation and set-up of the Grad-Rubin method. The modeled double inverse-J shaped Quasi-Separatrix Layer (QSL) footprints match the observed flare ribbons during the rising phase of the flare, including their hooked parts. The spiral-like shape of the latter may be related to a complex pre-eruptive flux rope with more than one turn of twist, as obtained in the model. These ribbon-associated flux-rope QSL-footprints are consistent with the new standard flare model in 3D, with the presence of a hyperbolic flux tube located below an inverse tear drop shaped coronal QSL. This is a new step forward forecasting the locations of reconnection and ribbons in solar flares, and the geometrical properties of eruptive flux ropes.

Authors: Jie Zhao, Stuart A. Gilchrist, Guillaume Aulanier, Brigitte Schmieder, Etienne Pariat, Hui Li

Publication Status: Accepted for publication in ApJ
Last Modified: 2016-03-30 20:56
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Temporal Evolution of the Magnetic Topology of the NOAA Active Region 11158  

Jie Zhao   Submitted: 2014-04-21 20:02

We studied the temporal evolution of the magnetic topology of the active region (AR) 11158 based on the reconstructed three-dimensional magnetic elds in the corona. The non-linear force-free eld (NLFFF) extrapolation method was applied to the 12 minutes cadence data obtained with the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) during ve days. By calculating the squashing degree factor Q in the volume, the derived quasi-separatrix layers (QSLs) show that this AR has an overall topology, resulting from a magnetic quadrupole, including an hyperbolic ux tube (HFT) con guration which is relatively stable at the time scale of the are ( 1 􀀀 2 hours). A strong QSL, which corresponds to some highly sheared arcades that might be related to the formation of a ux rope, is prominent just before the M6.6 and X2.2 ares, respectively. These facts indicate the close relationship between the strong QSL and the high are productivity of AR 11158. In addition, with a close inspection of the topology, we found a small-scale HFT which has an inverse teardrop structure above the aforementioned QSL before the X2.2 are. It indicates the existence of magnetic ux rope at this place. Even though a global con guration (HFT) is recognized in this AR, it turns out that the large-scale HFT only plays a secondary role during the eruption. In nal, we dismiss a trigger based on the breakout model and highlight the central role of the ux rope in the related eruption.

Authors: Jie Zhao, Hui Li, Etienne Pariat, Brigitte Schmieder, Yang Guo, Thomas Wiegelmann
Projects: SDO-HMI

Publication Status: Accepted by ApJ
Last Modified: 2014-04-23 09:01
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Statistical Study of Emerging Flux Regions and the Upper Atmosphere Response  

Jie Zhao   Submitted: 2012-07-04 19:42

We statistically study the property of emerging flux regions (EFRs) and the upper solar atmosphere response to the flux emergence by using data from the Helioseismic and Magnetic Imager (HMI) and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). Parameters including the total emerged flux, the flux growth rate, the maximum area, the duration of the emergence and the separation speed of the opposite polarities are adopted to delineate the property of the EFRs. The response of the upper atmosphere is addressed by the response of the atmosphere at different wavelengths (and thus at different temperatures). According to our results, the total emerged fluxes are in the range of (0.44 - 11.2) imes1019 Mx while the maximum area ranges from 17 to 182 arcsec2. The durations of the emergence are between 1 and 12 hours, which are positively correlated to both the total emerged flux and the maximum area. The maximum distances between the opposite polarities are 7 - 25 arcsec and are also correlated to the duration positively. The separation speeds are from 0.05 to 1.08 km s-1, negatively correlated to the duration. The derived flux growth rates are (0.1 - 1.3) imes1019 Mx hr-1, which are positively correlated to the total emerging flux. The upper atmosphere responds to the flux emergence in the 1600AA chromospheric line first, and then tens and hundreds of seconds later, in coronal lines, such as the 171AA (T=105.8 K) and 211AA (T=106.3 K) lines almost simultaneously, suggesting the successively heating of atmosphere from the chromosphere to the corona.

Authors: Zhao, Jie; Li, Hui
Projects: None

Publication Status: Accepted for publication in RAA
Last Modified: 2012-07-05 07:17
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Abstracts by Author
Observational Evidence of Magnetic Reconnection for Brightenings and Transition Region Arcades in IRIS observations
Hooked flare ribbons and flux-rope related QSL footprints
Temporal Evolution of the Magnetic Topology of the NOAA Active Region 11158
Statistical Study of Emerging Flux Regions and the Upper Atmosphere Response

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