Theory of magnetic connectivity in the solar corona

Titov, V. S.; Hornig, G.; Démoulin, P.

doi:10.1029/2001ja000278

Cited by 443 publications

(546 citation statements)

References 20 publications

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“…nulls or separators) or geometric features (e.g. quasi-separatrix layers, or QSLs, see Titov, Hornig, and Démoulin, 2002). In our case, we can definitively state that the reconnection modelled here is not associated with separators, separatrix surfaces, or magnetic nulls in any way.…”

Section: Comparison With Topological Reconnection Modelssupporting

confidence: 48%

Particle Acceleration Due to Coronal Non-null Magnetic Reconnection

2017

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Various topological features, for example magnetic null points and separators, have been inferred as likely sites of magnetic reconnection and particle acceleration in the solar atmosphere. In fact, magnetic reconnection is not constrained to solely take place at or near such topological features and may also take place in the absence of such features. Studies of particle acceleration using non-topological reconnection experiments embedded in the solar atmosphere are uncommon. We aim to investigate and characterise particle behaviour in a model of magnetic reconnection which causes an arcade of solar coronal magnetic field to twist and form an erupting flux rope, crucially in the absence of any common topological features where reconnection is often thought to occur. We use a numerical scheme that evolves the gyro-averaged orbit equations of single electrons and protons in time and space, and simulate the gyromotion of particles in a fully analytical global field model. We observe and discuss how the magnetic and electric fields of the model and the initial conditions of each orbit may lead to acceleration of protons and electrons up to 2 MeV in energy (depending on model parameters). We describe the morphology of time-dependent acceleration and impact sites for each particle species and compare our findings to those recovered by topologically based studies of three-dimensional (3D) reconnection and particle acceleration. We also broadly compare aspects of our findings to general observational features typically seen during two-ribbon flare events.

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Section: Comparison With Topological Reconnection Modelssupporting

confidence: 48%

Particle Acceleration Due to Coronal Non-null Magnetic Reconnection

2017

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“…The presence of a toroidal field component turns the neighbourhood of the X line into a hyperbolic flux tube (HFT) which consists of two intersecting quasi-separatrix layers with extremely diverging field lines (for a strict definition of HFTs, see Titov et al 2002). The existence of the HFT is generic to such force-free loop configurations with a nonvanishing net current , which is important for understanding the origin of sigmoidal structures in twisted configurations.…”

Section: Letter To the Editormentioning

confidence: 99%

Formation of current sheets and sigmoidal structure by the kink instability of a magnetic loop

Kliem

Titov

Török

2004

A&A

179

133

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Abstract.We study dynamical consequences of the kink instability of a twisted coronal flux rope, using the force-free coronal loop model by as the initial condition in ideal-MHD simulations. When a critical value of the twist is exceeded, the long-wavelength (m = 1) kink mode develops. Analogous to the well-known cylindrical approximation, a helical current sheet is then formed at the interface with the surrounding medium. In contrast to the cylindrical case, upward-kinking loops form a second, vertical current sheet below the loop apex at the position of the hyperbolic flux tube (generalized X line) in the model. The current density is steepened in both sheets and eventually exceeds the current density in the loop (although the kink perturbation starts to saturate in our simulations without leading to a global eruption). The projection of the field lines that pass through the vertical current sheet shows an S shape whose sense agrees with the typical sense of transient sigmoidal (forward or reverse S-shaped) structures that brighten in soft X rays prior to coronal eruptions. The upward-kinked loop has the opposite S shape, leading to the conclusion that such sigmoids do not generally show the erupting loops themselves but indicate the formation of the vertical current sheet below them that is the central element of the standard flare model.

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“…The location of QSLs can be determined by computing the squashing degree Q (Titov, Hornig, and Démoulin, 2002). A QSL is defined where Q ≫ 2 (the value Q = 2 is the lowest possible one).…”

Section: Qsls Locations and Flare Ribbonsmentioning

confidence: 99%

Homologous Flares and Magnetic Field Topology in Active Region NOAA 10501 on 20 November 2003

et al. 2010

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We present and interpret observations of two morphologically homologous flares that occurred in active region (AR) NOAA 10501 on 20 November 2003. Both flares displayed four homologous Hα ribbons and were both accompanied by coronal mass ejections (CMEs). The central flare ribbons were located at the site of an emerging bipole in the center of the active region. The negative polarity of this bipole fragmented in two main pieces, one rotating around the positive polarity by ≈ 110 • within 32 hours. We model the coronal magnetic field and compute its topology, using as boundary condition the magnetogram closest in time to each flare. In particular, we calculate the location of quasiseparatrix layers (QSLs) in order to understand the connectivity between the flare ribbons. Though several polarities were present in AR 10501, the global magnetic field topology corresponds to a quadrupolar magnetic field distribution without magnetic null points. For both flares, the photospheric traces of QSLs are similar and match well the locations of the four Hα ribbons. This globally unchanged topology and the continuous shearing by the rotating bipole are two key factors responsible for the flare homology. However, our analyses also indicate that different magnetic connectivity domains of the quadrupolar configuration become unstable during each flare, so that magnetic reconnection proceeds differently in both events.

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Theory of magnetic connectivity in the solar corona

Cited by 443 publications

References 20 publications

Particle Acceleration Due to Coronal Non-null Magnetic Reconnection

Particle Acceleration Due to Coronal Non-null Magnetic Reconnection

Formation of current sheets and sigmoidal structure by the kink instability of a magnetic loop

Homologous Flares and Magnetic Field Topology in Active Region NOAA 10501 on 20 November 2003

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