Response of the Photospheric Magnetic Field to the X2.2 Flare on 2011 February 15

The Astrophysical Journal Letters (Impact Factor: 5.6). 12/2011; 745(2). DOI: 10.1088/2041-8205/745/2/L17
Source: arXiv

ABSTRACT It is well known that the long-term evolution of the photospheric magnetic
field plays an important role in building up free energy to power solar
eruptions. Observations, despite being controversial, have also revealed a
rapid and permanent variation of the photospheric magnetic field in response to
the coronal magnetic field restructuring during the eruption. The Helioseismic
and Magnetic Imager instrument (HMI) on board the newly launched Solar Dynamics
Observatory (SDO) produces seeing-free full-disk vector magnetograms at
consistently high resolution and high cadence, which finally makes possible an
unambiguous and comprehensive study of this important back-reaction process. In
this study, we present a near disk-center, GOES -class X2.2 flare, which
occurred in NOAA AR 11158 on 2011 February 15. Using the magnetic field
measurements made by HMI, we obtained the first solid evidence of a rapid (in
about 30 minutes) and irreversible enhancement in the horizontal magnetic field
at the flaring magnetic polarity inversion line (PIL) by a magnitude of ~30%.
It is also shown that the photospheric field becomes more sheared and more
inclined. This field evolution is unequivocally associated with the flare
occurrence in this sigmoidal active region, with the enhancement area located
in between the two chromospheric flare ribbons and the initial conjugate hard
X-ray footpoints. These results strongly corroborate our previous conjecture
that the photospheric magnetic field near the PIL must become more horizontal
after eruptions, which could be related to the newly formed low-lying fields
resulted from the tether-cutting reconnection.

  • Astronomy and Astrophysics 10/2013; 558:A76. · 4.48 Impact Factor
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    ABSTRACT: Context. The standard CSHKP model for eruptive flares is two-dimensional. Yet observational interpretations of photospheric currents in pre-eruptive sigmoids, shear in post-flare loops, and relative positioning and shapes of flare ribbons, all together require three-dimensional extensions to the model. Aims: We focus on the strong-to-weak shear transition in post-flare loops, and on the time-evolution of the geometry of photospheric electric currents, which occur during the development of eruptive flares. The objective is to understand the three-dimensional physical processes, which cause them, and to know how much the post-flare and the pre-eruptive distributions of shear depend on each other. Methods: The strong-to-weak shear transition in post-flare loops is identified and quantified in a flare observed by STEREO, as well as in a magnetohydrodynamic simulation of CME initiation performed with the OHM code. In both approaches, the magnetic shear is evaluated with field line footpoints. In the simulation, the shear is also estimated from ratios between magnetic field components. Results: The modeled strong-to-weak shear transition in post-flare loops comes from two effects. Firstly, a reconnection-driven transfer of the differential magnetic shear, from the pre- to the post-eruptive configuration. Secondly, a vertical straightening of the inner legs of the CME, which induces an outer shear weakening. The model also predicts the occurrence of narrow electric current layers inside J-shaped flare ribbons, which are dominated by direct currents. Finally, the simulation naturally accounts for energetics and time-scales for weak and strong flares, when typical scalings for young and decaying solar active regions are applied. Conclusions: The results provide three-dimensional extensions to the standard flare model. These extensions involve MHD processes that should be tested with observations.
    Astronomy and Astrophysics 07/2012; · 4.48 Impact Factor
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    ABSTRACT: For the first time, the kinematic evolution of a coronal wave over the entire solar surface is studied. Full Sun maps can be made by combining images from the Solar Terrestrial Relations Observatory satellites, Ahead and Behind, and the Solar Dynamics Observatory, thanks to the wide angular separation between them. We study the propagation of a coronal wave, also known as the "Extreme Ultraviolet Imaging Telescope" wave, and its interaction with a coronal hole (CH) resulting in secondary waves and/or reflection and transmission. We explore the possibility of the wave obeying the law of reflection. In a detailed example, we find that a loop arcade at the CH boundary cascades and oscillates as a result of the extreme ultraviolet (EUV) wave passage and triggers a wave directed eastward that appears to have reflected. We find that the speed of this wave decelerates to an asymptotic value, which is less than half of the primary EUV wave speed. Thanks to the full Sun coverage we are able to determine that part of the primary wave is transmitted through the CH. This is the first observation of its kind. The kinematic measurements of the reflected and transmitted wave tracks are consistent with a fast-mode magnetohydrodynamic wave interpretation. Eventually, all wave tracks decelerate and disappear at a distance. A possible scenario of the whole process is that the wave is initially driven by the expanding coronal mass ejection and subsequently decouples from the driver and then propagates at the local fast-mode speed.
    The Astrophysical Journal 09/2012; 756(2):143-. · 6.28 Impact Factor

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