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

The Astrophysical Journal Letters (Impact Factor: 5.34). 12/2011; 745(2). DOI: 10.1088/2041-8205/745/2/L17
Source: arXiv


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.

Download full-text


Available from: Shuo Wang, Jan 29, 2014
1 Follower
19 Reads
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We perform a statistical study of permanent changes in longitudinal fields associated with solar flares by tracking magnetic features. The YAFTA feature tracking algorithm is applied to GONG++ 1-minute magnetograms for 77 X-class and M-class flares to analyze the evolution and interaction of the magnetic features and to estimate the amount of canceled magnetic flux. We find that significantly more magnetic flux decreases than increases occurred during the flares, consistent with a model of collapsing loop structure for flares. Correlations between both total (unsigned) and net (signed) flux changes and the GOES peak X-ray flux are dominated by X-class flares at limb locations. The flux changes were accompanied in most cases by significant cancellation, most of which occurred during the flares. We find that the field strength and complexity near the polarity inversion line are approximately equally important in the flux cancellation processes that accompany the flares. We do not find a correlation between the flux cancellation events and the stepwise changes in the magnetic flux in the region.
    Solar Physics 04/2013; 283(2). DOI:10.1007/s11207-013-0241-8 · 4.04 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Horizontal proper motions were measured with local correlation tracking (LCT) techniques in active region NOAA 11158 on 2011 February 15 at a time when a major (X2.2) solar flare occurred. The measurements are based on continuum images and magnetograms of the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. The observed shear flows along the polarity inversion line were rather weak (a few 100 m s −1). The counter-streaming region shifted toward the north after the flare. A small circular area with flow speeds of up to 1.2 km s −1 appeared after the flare near a region of rapid penumbral decay. The LCT signal in this region was provided by small-scale photospheric brigthenings, which were associated with fast traveling moving magnetic features. Umbral strengthening and rapid penumbral decay was observed after the flare. Both phenomena were closely tied to kernels of white-light flare emission. The white-light flare only lasted for about 15 min and peaked 4 min earlier than the X-ray flux. In comparison to other major flares, the X2.2 flare in active region NOAA 11158 only produced diminutive photospheric signatures.
    Astronomische Nachrichten 02/2012; 999(2):1-6. DOI:10.1002/asna.201111631 · 0.92 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: An accepted model for magnetospheric substorms is proposed as the basis for a generic model for magnetic explosions, and is applied to solar flares. The model involves widely separated energy-release and particle-acceleration regions, with energy transported Alfv\'enically between them. On a global scale, these regions are coupled by a large-scale current that is set up during the explosion by redirection of pre-existing current associated with the stored magnetic energy. The explosion-related current is driven by an electromotive force (EMF) due to the changing magnetic flux enclosed by this current. The current path and the EMF are identified for an idealized quadrupolar model for a flare.
    The Astrophysical Journal 02/2012; 749(1). DOI:10.1088/0004-637X/749/1/58 · 5.99 Impact Factor
Show more