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Author name code: toeroek
ADS astronomy entries on 2022-09-14
author:"Toeroek, Tibor" 

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Title: A Magnetogram-matching Method for Energizing Magnetic Flux
    Ropes Toward Eruption
Authors: Titov, V. S.; Downs, C.; Török, T.; Linker, J. A.
2022ApJ...936..121T    Altcode: 2022arXiv220503982T
  We propose a new "helicity-pumping" method for energizing coronal
  equilibria that contain a magnetic flux rope (MFR) toward an
  eruption. We achieve this in a sequence of magnetohydrodynamics
  relaxations of small line-tied pulses of magnetic helicity, each of
  which is simulated by a suitable rescaling of the current-carrying
  part of the field. The whole procedure is "magnetogram-matching"
  because it involves no changes to the normal component of the field
  at the photospheric boundary. The method is illustrated by applying
  it to an observed force-free configuration whose MFR is modeled
  with our regularized Biot-Savart law method. We find that, in spite
  of the bipolar character of the external field, the MFR eruption is
  sustained by two reconnection processes. The first, which we refer to
  as breakthrough reconnection, is analogous to breakout reconnection
  in quadrupolar configurations. It occurs at a quasi-separator inside a
  current layer that wraps around the erupting MFR and is caused by the
  photospheric line-tying effect. The second process is the classical
  flare reconnection, which develops at the second quasi-separator inside
  a vertical current layer that is formed below the erupting MFR. Both
  reconnection processes work in tandem with the magnetic forces of the
  unstable MFR to propel it through the overlying ambient field, and their
  interplay may also be relevant for the thermal processes occurring in
  the plasma of solar flares. The considered example suggests that our
  method will be beneficial for both the modeling of observed eruptive
  events and theoretical studies of eruptions in idealized magnetic
  configurations.

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Title: What are the Limits to Extreme Eruptions on the Sun?
Authors: Linker, Jon; Riley, Pete; Titov, Viacheslav; Lionello,
   Roberto; Downs, Cooper; Torok, Tibor; Caplan, Ronald
2022cosp...44.1560L    Altcode:
  Extreme solar eruptions are of great interest, for both purely
  scientific as well as practical reasons. The 1859 Carrington event
  is often considered to represent the largest extreme of space weather
  events. However, so-called superflares (energies from 1e33-1e35 ergs)
  on other stars hint at even more acute possibilities. What are the
  energy limits for solar eruptions? The energy that powers these events
  is believed to be stored as free magnetic energy (energy above the
  potential field state) prior to eruption. Therefore, the maximum free
  energy that can be stored in an active region (AR) bounds the largest
  possible eruption that can be released from a region. According to the
  Aly-Sturrock theorem, the energy of a fully force-free field cannot
  exceed the energy of the so-called open field. If the theorem holds,
  this places an upper limit on the amount of free energy that can be
  stored: the maximum free energy (MFE) is the difference between the open
  field energy and the potential field energy of the active region. We
  computed the MFE for some of the most flare productive ARs of solar
  cycles 22-24 and found 6 cases where the maximum possible energy storage
  was on the order of or greater than 1e34 ergs. In simulation studies,
  we have found that while the MFE is indeed a useful upper bound,
  it is generally larger than the maximum energy that can actually
  be stored. We have found that the related theory of partially open
  fields can provide a more stringent upper bound - the partially open
  field energy (POFE). We calculate POFEs for several significant ARs of
  cycles 22-24 and revisit their energy storage limits. Work supported
  by NSF and NASA.

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Title: Suppression of Torus Instability on Cool Stars
Authors: Sun, Xudong; Derosa, Marc; Torok, Tibor
2022cosp...44.1389S    Altcode:
  Despite the frequent detection of stellar super flares, reports on
  stellar coronal mass ejections (CMEs) are rare. This is in contrast with
  our Sun, where almost all large flares are accompanied by a CME. Here,
  we use an analytical coronal magnetic field model to demonstrate that
  the torus instability, a leading mechanism for solar CMEs, tends to
  be suppressed in stellar magnetic environment. Contributing factors
  include larger starspots, stronger global dipole field, and more
  closed magnetic geometry compared to the Sun. Suppression of the torus
  instability may contribute to the low apparent CME rate on cool stars.

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Title: Early Dynamics and Trajectories of CMEs
Authors: Zhang, Jie; Torok, Tibor; Nikou, Eleni; Nazmus Sakib, Md;
   Dhakal, Suman
2022cosp...44.1359Z    Altcode:
  How CMEs evolve right after their initiation is of high interest
  for solar physics research and space weather predictions. Important
  properties such as their speed and trajectory are largely set during
  this early phase of evolution. However, the underlying conditions and
  physical mechanisms remain poorly understood, both observationally and
  theoretically. In this study, we perform a comprehensive investigation
  of the kinematic, geometric and morphological evolution of CMEs from
  the very beginning of their eruption near the surface of the Sun
  continuously until they reach the outer corona. In particular, we
  study three CMEs that originated near the disk center, but exhibited
  significantly different behavior in terms of their rise direction
  or deflection: the deflection angles (measured along both longitude
  and latitude) varies from >20 degree to nearly zero degree for
  these events. We employ a novel technique to determine the true early
  propagation direction of disk-centered CMEs, using high cadence EUV
  observation from SDO/AIA. Our technique is based on fitting the shape
  of observed EUV waves, which are presumably driven by the expanding
  magnetic flux rope. We further use STEREO/COR1 and COR2 observations,
  in combination with SOHO/LASCO data, to determine the 3D trajectory
  and morphology of CMEs in the outer corona. We also investigate the
  properties of the magnetic field in the source regions of these CMEs, in
  order to determine the causes of observed evolution both qualitatively
  and quantitatively. We also compare our observational results with
  data-constrained state-of-the-art 3D MHD numerical simulation of
  specific events. Our work addresses the following scientific questions:
  (1) What determines the trajectory of a rising CME? (2) Can we constrain
  and/or predict the trajectory of a potential CME from models?

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Title: The 3D magnetic structure of CMEs throughout the extended
    solar corona
Authors: Palmerio, Erika; Downs, Cooper; Torok, Tibor; Ben-Nun, Michal
2022cosp...44.1128P    Altcode:
  The magnetic fields that make up the internal structure of coronal
  mass ejections (CMEs) are thought to be organised in a flux-rope
  configuration consisting of twisted magnetic fields that wind about
  a central axis. Remote-sensing observations of CMEs show a wide
  range of morphologies, dynamics, and evolution, including rotation,
  non-uniform expansion, deflection, and interaction with the ambient
  solar wind. In-situ measurements, however, typically consist of a single
  1D spacecraft trajectory through a large 3D structure (or few at best),
  limiting our understanding of how the internal magnetic structure of
  a given CME may vary in time and space. In this work, we analyse the
  magnetic configuration of an idealised CME during its early evolution
  in the range 1-30 Rs, using the Magnetohydrodynamic Algorithm Outside
  a Sphere (MAS) code. The initial flux rope erupts in a simplified
  coronal configuration, from a bipolar active region located under
  the streamer belt, and propagates through a uniform background solar
  wind. We place a fleet of synthetic spacecraft throughout the CME's
  path at different combinations of heliocentric distance, latitude,
  and longitude. We identify and examine flux-rope signatures in the
  synthetic in-situ profiles, in order to characterise radial variations
  as well as latitudinal/longitudinal ones. We find that, even in the
  case of a simplified CME erupting under solar minimum-like conditions,
  the sampling location significantly affects the global structure that
  would be deduced from common flux-rope reconstruction and analysis
  techniques used for in-situ measurements.

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Title: The Pre-Eruptive Structure and Initiation Mechanism(s) of CMEs
Authors: Torok, Tibor
2022cosp...44.2461T    Altcode:
  Coronal mass ejections (CMEs) are huge expulsions of magnetized
  plasma from the low solar corona into interplanetary space, and
  the main driver of space weather disturbances in the terrestrial
  magnetosphere. Despite extensive research being conducted since the
  discovery of CMEs about 50 years ago, many important aspects of these
  enigmatic events are still not well understood. In this presentation, I
  will address two of these aspects, namely the nature of the pre-eruptive
  magnetic configuration and the physical mechanism(s) by which CME are
  triggered and driven. Specifically, I will discuss how numerical (MHD)
  simulations can help us to improve our understanding of CMEs.

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Title: The first widespread solar energetic particle event of solar
    cycle 25 on 2020 November 29. Shock wave properties and the wide
    distribution of solar energetic particles
Authors: Kouloumvakos, A.; Kwon, R. Y.; Rodríguez-García, L.; Lario,
   D.; Dresing, N.; Kilpua, E. K. J.; Vainio, R.; Török, T.; Plotnikov,
   I.; Rouillard, A. P.; Downs, C.; Linker, J. A.; Malandraki, O. E.;
   Pinto, R. F.; Riley, P.; Allen, R. C.
2022A&A...660A..84K    Altcode:
  Context. On 2020 November 29, an eruptive event occurred in an active
  region located behind the eastern solar limb as seen from Earth. The
  event consisted of an M4.4 class flare, a coronal mass ejection,
  an extreme ultraviolet (EUV) wave, and a white-light (WL) shock
  wave. The eruption gave rise to the first widespread solar energetic
  particle (SEP) event of solar cycle 25, which was observed at four
  widely separated heliospheric locations (∼230°). <BR /> Aims: Our
  aim is to better understand the source of this widespread SEP event,
  examine the role of the coronal shock wave in the wide distribution
  of SEPs, and investigate the shock wave properties at the field lines
  magnetically connected to the spacecraft. <BR /> Methods: Using EUV
  and WL data, we reconstructed the global three-dimensional structure of
  the shock in the corona and computed its kinematics. We determined the
  magnetic field configurations in the corona and interplanetary space,
  inferred the magnetic connectivity of the spacecraft with the shock
  surface, and derived the evolution of the shock parameters at the
  connecting field lines. <BR /> Results: Remote sensing observations
  show formation of the coronal shock wave occurring early during the
  eruption, and its rapid propagation to distant locations. The results
  of the shock wave modelling show multiple regions where a strong
  shock has formed and efficient particle acceleration is expected
  to take place. The pressure/shock wave is magnetically connected to
  all spacecraft locations before or during the estimated SEP release
  times. The release of the observed near-relativistic electrons occurs
  predominantly close to the time when the pressure/shock wave connects to
  the magnetic field lines or when the shock wave becomes supercritical,
  whereas the proton release is significantly delayed with respect to the
  time when the shock wave becomes supercritical, with the only exception
  being the proton release at the Parker Solar Probe. <BR /> Conclusions:
  Our results suggest that the shock wave plays an important role in the
  spread of SEPs. Supercritical shock regions are connected to most of the
  spacecraft. The particle increase at Earth, which is barely connected
  to the wave, also suggests that the cross-field transport cannot be
  ignored. The release of energetic electrons seems to occur close to
  the time when the shock wave connects to, or becomes supercritical at,
  the field lines connecting to the spacecraft. Energetic protons are
  released with a time-delay relative to the time when the pressure/shock
  wave connects to the spacecraft locations. We attribute this delay
  to the time that it takes for the shock wave to accelerate protons
  efficiently. <P />Movie associated to Fig. 2 is available at <A
  href="https://www.aanda.org/10.1051/0004-6361/202142515/olm">https://www.aanda.org</A>

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Title: A Model of Homologous Confined and Ejective Eruptions Involving
    Kink Instability and Flux Cancellation
Authors: Hassanin, Alshaimaa; Kliem, Bernhard; Seehafer, Norbert;
   Török, Tibor
2022ApJ...929L..23H    Altcode: 2022arXiv220411767H
  In this study, we model a sequence of a confined and a full eruption,
  employing the relaxed end state of the confined eruption of a
  kink-unstable flux rope as the initial condition for the ejective
  one. The full eruption, a model of a coronal mass ejection, develops
  as a result of converging motions imposed at the photospheric
  boundary, which drive flux cancellation. In this process, parts of
  the positive and negative external flux converge toward the polarity
  inversion line, reconnect, and cancel each other. Flux of the same
  amount as the canceled flux transfers to a flux rope, increasing
  the free magnetic energy of the coronal field. With sustained flux
  cancellation and the associated progressive weakening of the magnetic
  tension of the overlying flux, we find that a flux reduction of ≍11%
  initiates the torus instability of the flux rope, which leads to a full
  eruption. These results demonstrate that a homologous full eruption,
  following a confined one, can be driven by flux cancellation.

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Title: Torus-stable zone above starspots
Authors: Sun, Xudong; Török, Tibor; DeRosa, Marc L.
2022MNRAS.509.5075S    Altcode: 2021arXiv211103665S; 2021MNRAS.tmp.2934S
  Whilst intense solar flares are almost always accompanied by a coronal
  mass ejection (CME), reports on stellar CMEs are rare, despite the
  frequent detection of stellar 'super flares'. The torus instability of
  magnetic flux ropes is believed to be one of the main driving mechanisms
  of solar CMEs. Suppression of the torus instability, due to a confining
  background coronal magnetic field that decreases sufficiently slowly
  with height, may contribute to the lack of stellar CME detection. Here,
  we use the solar magnetic field as a template to estimate the vertical
  extent of this 'torus-stable zone' (TSZ) above a stellar active
  region. For an idealized potential field model comprising the fields
  of a local bipole (mimicking a pair of starspots) and a global dipole,
  we show that the upper bound of the TSZ increases with the bipole
  size, the dipole strength, and the source surface radius where the
  coronal field becomes radial. The boundaries of the TSZ depend on the
  interplay between the spots' and the dipole's magnetic fields, which
  provide the local- and global-scale confinement, respectively. They
  range from about half the bipole size to a significant fraction of the
  stellar radius. For smaller spots and an intermediate dipole field,
  a secondary TSZ arises at a higher altitude, which may increase the
  likelihood of 'failed eruptions'. Our results suggest that the low
  apparent CME occurrence rate on cool stars is, at least partially,
  due to the presence of extended TSZs.

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Title: Magnetogram-matching Energization and Eruption of Magnetic
    Flux Ropes
Authors: Titov, Viacheslav; Downs, Cooper; Torok, Tibor; Linker, Jon
2021AGUFMSH32A..04T    Altcode:
  We propose a new technique for energizing coronal magnetic equilibria
  toward eruptions. We achieve this via a sequence of MHD relaxations
  of small line-tied pulses of magnetic helicity, each of which is
  simulated by a suitable rescaling of the current-carrying part of
  the field. The whole procedure is 'magnetogram-matching' because
  it involves no changes to the normal component of the field at the
  lower boundary. The technique is illustrated by application to bipolar
  force-free configurations whose magnetic flux ropes (MFRs) are modeled
  with our regularized Biot-Savart law method. We have found that, in
  spite of the bipolar character of the ambient potential field in these
  examples, the resulting MFR eruption is generally sustained by two
  reconnection processes. The first, which we refer to as breakthrough
  reconnection, is analogous to breakout reconnection in quadrupolar
  configurations. It occurs at a quasi-separator field line located inside
  the current layer that wraps around the erupting MFR, and results from
  taking into account the line-tying effect at the photosphere. The second
  process is the classical tether-cutting reconnection that develops at
  the second quasi-separator inside a vertical current layer formed below
  the erupting MFR. Both reconnection processes work in tandem to propel
  the MFR through the overlying ambient field. The considered examples
  suggest that our technique will be beneficial for both the modeling
  of particular eruptive events and theoretical studies of eruptions
  in idealized magnetic configurations. This research was supported by
  NASA programs HTMS (award no. 80NSSC20K1274) and HSR (80NSSC19K0858
  and 80NSSC20K1317); NASA/ NSF program DRIVE (80NSSC20K0604); and NSF
  grants AGS-1135432, AGS-1923377, and ICER-1854790.

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Title: Propagation and Deflection of CMEs in Different Background
    Magnetic Fields
Authors: Ben-Nun, Michal; Torok, Tibor; Downs, Cooper; Caplan, Ronald;
   Lionello, Roberto
2021AGUFMSH35B2043B    Altcode:
  As suggested by Isenberg and Forbes (2007) and demonstrated numerically
  by Kliem et al. (2012), the Lorentz forces stemming from the interaction
  of the axial current in an erupting magnetic flux rope (MFR) with an
  ambient magnetic-field component that has the same orientation as the
  initial MFR axis lead to a rotation of the top part of the MFR about
  its rise direction. In principle, the same mechanism can be applied to
  CMEs that propagate in a unipolar radial field in the corona or inner
  heliosphere. In such cases, however, the corresponding forces should
  not lead to a rotation, but to a deflection of the CME front, thereby
  significantly altering the CME's magnetic orientation. Apart from a
  brief consideration in Lugaz et al. (2011), such deflections have, to
  the best of our knowledge, not yet been studied systematically. Here
  we employ three-dimensional (3D) idealized magnetohydrodynamic
  (MHD) simulations to investigate this effect in background fields of
  increasing complexity. We first consider a freely expanding toroidal
  MFR in a uniform background field, as well as the propagation of a
  compact, line-tied MFR in a unipolar radial field. In both cases,
  we find significant deflections. We then use a more realistic setup,
  in which we erupt an MFR from a localized, bipolar source region into
  a global dipole field and solar wind, which allows for a significant
  expansion of the MFR before it encounters an open field. We perform a
  parametric study in which we vary the location and magnetic orientation
  of the source region, as well as the handedness (helicity sign) of the
  MFR. In this presentation, we discuss the influence of these parameters
  on the CME trajectory, and on other important CME properties such as
  its speed, morphology, and interaction (reconnection) with the ambient
  magnetic field.

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Title: Theory and Models of Flare/CME Onset Via Flux Emergence and/or
    Shear Flows
Authors: Linton, Mark; Torok, Tibor; Lynch, Benjamin
2021AGUFMSH35B2042L    Altcode:
  The onset of eruptive flare energy release requires both a buildup
  of stored energy and a trigger for the release of that energy. This
  talk will review key models of how this storage and release occurs in
  solar eruptions, in particular for breakout eruptions and for torus
  instability eruptions. In both cases, the eruptions require the buildup
  of free magnetic energy in the form of sheared field. For the breakout
  mechanism the energy is built up as sheared magnetic fields in coronal
  arcades, while for the torus instability the energy is built up as a
  combination of axial and twist field in coronal flux ropes. We will
  review recent work on the buildup of this energy to eruptive states,
  both via velocity shearing at the photosphere and via the emergence of
  sheared flux from the convection zone into the corona. Then we will
  review recent work exploring how the emergence of new magnetic flux
  into the corona can act as a trigger for these eruptive events. Much
  of the recent work to be discussed here is being carried out within
  the framework of NASAs Living with a Star focused science team
  on Understanding the Onset of Major Solar Eruptions. This work is
  supported by the NASA Living with a Star program. Distribution A:
  Approved for public release: distribution unlimited

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Title: Evolution of Non-neutralized Electric Currents in Eruptive
    Solar Active Regions
Authors: Prazak, Michael; Downs, Cooper; Torok, Tibor; Jiong, Qiu;
   Titov, Viacheslav
2021AGUFMSH35B2036P    Altcode:
  We study the evolution of several solar active regions (ARs)
  that produced both fast (&gt;600 km/s) and slow (&lt;600 km/s)
  coronal mass ejections (CMEs). We have been analyzing the vector
  magnetic field measurements for the ARs during their disk passage,
  and our preliminary results suggest that the ARs produced slow CMEs
  throughout the observed period and fast CMEs only in the presence
  of strong non-neutralized electric currents. We have also analyzed
  the temporal and spatial evolution of non-neutralized currents in
  NOAA AR 11305, which produced an M-class eruptive flare. Strong
  non-neutralized currents, associated with emerging flux and shear
  flows, were located along the magnetic polarity inversion line. The
  observations suggest the presence of a magnetic flux rope (MFR), which
  evolved and erupted, forming flare ribbons that encompass the areas
  of strong current. The regularized Biot-Savart laws (rBSLs; Titov
  et. al. 2018) formalism and a zero-$\beta$ magnetohydrodynamic (MHD)
  model were employed to construct the aforementioned MFR and to follow
  its evolution. The spatial location and the amount of non-neutralized
  currents computed from the model well agree with the observational
  measurements. This result suggests that the development of the MFR,
  which can be identified by sustained and concentrated photospheric
  non-neutralized electric currents, is an important element for the
  production of the CME in this study. This work is supported by NASA
  programs HSR (80NSSC20K1317) and HGI (80NSSC18K0622).

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Title: Partially Open Fields as the Energy Bounds for Solar Eruptions
Authors: Linker, Jon; Downs, Cooper; Caplan, Ronald; Kazachenko,
   Maria; Torok, Tibor; Titov, Viacheslav; Lionello, Roberto; Riley, Pete
2021AGUFMSH42B..02L    Altcode:
  The energy source for major solar eruptions, such as flare and coronal
  mass ejections (CMEs), is recognized to originate in the solar magnetic
  field. Specifically, it is believed to be the release of the free
  magnetic energy (energy above the potential field state) stored in
  the field prior to eruption. A key question for both predicting future
  eruptions and estimating their possible magnitude is, what is the bound
  to this energy? The Aly-Sturrock theorem shows that the energy of a
  fully force-free field cannot exceed the energy of the so-called open
  field. If the theorem holds, this places an upper limit on the amount
  of free energy that can be stored. In recent simulations, we have found
  that the energy of a closely related field, the partially open field
  (POF), can place a useful bound on the energy of an eruption from real
  active regions, a much tighter constraint than the energy of the fully
  open field. We are using a database of flare ribbons (Kazachenko et al.,
  ApJ 845, 2017) to test this idea observationally. A flare ribbon mask
  is defined as the area swept out by the ribbons during the flare. It
  can serve as a proxy for the region of the field that opened during the
  eruption. In a preliminary study, we used the ribbon masks to define
  the POF for several large events originating in solar cycle 24 active
  regions, and computed the energy of the POF. Our results suggested a
  strong correlation of energy release in solar events and the POF. In
  this presentation, we describe a continuation of this study, extending
  it to a significant number of the M and X class flare occurring in
  solar cycle 24. Work supported by NASA and NSF.

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Title: Flux rope reformation as a model for homologous solar flares
    and coronal mass ejections
Authors: Saad Hassanin, Alshaimaa; Kliem, Bernhard; Torok, Tibor;
   Seehafer, Norbert
2021AGUFMSH32A..09S    Altcode:
  In this study we model for the first time a sequence of a confined
  and a full eruption, employing the flux rope reformed in the confined
  eruption as the initial condition for the ejective one. The full
  eruption develops as a result of imposed converging motions in the
  photospheric boundary which drive flux cancellation. In this process,
  a part of the positive and negative sunspot flux converge toward
  the polarity inversion line, reconnect, and cancel each other. Flux
  of the same amount as the canceled flux transfers to the flux rope,
  building up free magnetic energy. With sustained flux cancellation
  and the associated progressive weakening of the magnetic tension of
  the overlying flux, we find that a flux reduction of 8.9% leads to the
  ejective eruption. These results demonstrate that homologous eruptions,
  eventually leading to a coronal mass ejection (CME), can be driven by
  flux cancellation.

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Title: Tracking and Understanding the Trajectory of CMEs From Birth
    to Late Stage
Authors: Zhang, Jie; Sakib, Md Nazmus; Torok, Tibor; Dhakal, Suman;
   Nikou, Eleni
2021AGUFMSH35B2059Z    Altcode:
  We present a detailed observational study of the trajectory of coronal
  mass ejections (CMEs) from their onset continuously to the late stage
  of evolution in the outer corona. The 3-D trajectory of CMEs, along with
  their sizes, kinematics and internal magnetic structure, determines the
  full global state of a CME and how it evolves in the interplanetary
  space. These properties are essential for understanding their
  evolution, their interaction with the interplanetary magnetic field
  and plasma, and ultimately their geoeffectiveness and space weather
  consequences. Changes of the CME trajectory, often referred to as
  deflection or channeling, have been observed mostly in the outer corona
  and/or for events that originate near the solar limb. Measurements
  of the early trajectory of CMEs that originate near the center of
  the solar disk are rare, due to the limitation of coronagraphic
  observations. However, these CMEs are of particular interest since
  they are mor likely to hit the Earth and the likelihood of hitting is
  sensitive to the trajectory. Here we present a novel technique for
  determining CME trajectories near the solar surface, which employs
  SDO/AIA observations and is based on the shape of coronal waves driven
  by the CME expansion. We further use STEREO/COR1 and COR2 observations,
  in combination with SOHO/LASCO data, to determine the 3D trajectory of
  CMEs in the inner and outer corona, respectively. This study addresses
  the following two main questions: (1) What are the rise directions of
  CMEs right after the onset of the eruption and how do they change as
  a function of height above the solar surface? (2) Are deviations from
  a radial trajectory caused primarily by the deflection of the CME at
  coronal holes or by the magnetic properties of the CME's source region?

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Title: Torus-Stable Zone Above Starspots
Authors: Sun, Xudong; Torok, Tibor; DeRosa, Marc
2021AGUFMSH32A..02S    Altcode:
  The torus instability (TI) of magnetic flux ropes is one of the main
  driving mechanisms of solar coronal mass ejections (CMEs). If the
  stabilizing background magnetic field decreases sufficiently slowly
  with height, the TI will be suppressed. Here we estimate the vertical
  extent of this "torus-stable zone" (TSZ) above starspots using the
  solar magnetic field as a template. For a potential field comprising
  a bipole as a pair of starspots and a global dipole, we show that the
  upper bound of the TSZ increases with the bipole size, the dipole
  strength, and the source surface radius where the coronal field
  becomes radial. The values depend on the interplay between the spot
  and dipole magnetic fields, which provide the local and global-scale
  confinement, respectively. They range from about half the bipole size
  to a significant fraction of the stellar radius. A secondary TSZ
  sometimes arises at a higher altitude which may facilitate "failed
  eruptions". The suppression of the TI may contribute to the lack of
  CME detection on cool stars, as larger starspots, stronger dipole,
  and more closed magnetic topology significantly expand the TSZ.

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Title: Optimization of Magnetic Flux Ropes Modeled with the
    Regularized Biot-Savart Law Method
Authors: Titov, V. S.; Downs, C.; Török, T.; Linker, J. A.; Caplan,
   R. M.; Lionello, R.
2021ApJS..255....9T    Altcode: 2021arXiv210602789T
  The so-called regularized Biot-Savart laws (RBSLs) provide an efficient
  and flexible method for modeling pre-eruptive magnetic configurations
  of coronal mass ejections (CMEs) whose characteristics are constrained
  by observational images and magnetic field data. This method allows
  one to calculate the field of magnetic flux ropes (MFRs) with small
  circular cross sections and an arbitrary axis shape. The field of
  the whole configuration is constructed as a superposition of (1)
  such a flux-rope field and (2) an ambient potential field derived, for
  example, from an observed magnetogram. The RBSL kernels are determined
  from the requirement that the MFR field for a straight cylinder must
  be exactly force free. For a curved MFR, however, the magnetic forces
  are generally unbalanced over the whole path of the MFR. To minimize
  these forces, we apply a modified Gauss-Newton method to find optimal
  MFR parameters. This is done by iteratively adjusting the MFR axis
  path and axial current. We then try to relax the resulting optimized
  configuration in a subsequent line-tied zero-beta magnetohydrodynamic
  simulation toward a force-free equilibrium. By considering two models of
  the sigmoidal pre-eruption configuration for the 2009 February 13 CME,
  we demonstrate how this approach works and what it is capable of. We
  show, in particular, that the building blocks of the core magnetic
  structure described by these models match morphological features
  typically observed in such types of configurations. Our method will
  be useful for both the modeling of particular eruptive events and
  theoretical studies of idealized pre-eruptive MFR configurations.

---------------------------------------------------------
Title: The Upgraded RBSL Method Applied To The Modeling Of Sigmoidal
    Pre-eruptive Magnetic Configurations
Authors: Titov, V. S.; Torok, T.; Downs, C.; Linker, J.; Caplan, R.;
   Lionello, R.
2021AAS...23821312T    Altcode:
  The so-called regularized Biot-Savart laws (RBSLs, Titov et al.,
  ApJL 2018) provide an efficient and flexible method for constructing
  pre-eruptive configurations (PECs) whose characteristics are constrained
  by remote-sensing observations. This method allows one to calculate the
  field of magnetic flux ropes (MFRs) of small diameters and an arbitrary
  axis shape. The field of the PEC is generally a superposition of (1)
  such an MFR field, (2) an ambient potential field determined, e.g.,
  by the radial field component of an observed magnetogram, and (3) a
  so-called compensating potential field that counteracts perturbations
  of the radial field by the MFR at the boundary. The constructed
  PEC is then relaxed in a line-tied zero-beta MHD simulation toward a
  force-free equilibrium. <P />We have recently upgraded our method in two
  ways. First, we have reformulated the RBSLs so that the compensating
  field can be neglected if the distance between the MFR footprints
  is much less than the solar radius. Second, we have developed an
  optimization method to minimize unbalanced magnetic forces prior to
  the MHD relaxation of a modeled PEC. This minimization is obtained by
  optimizing the shape and axial current of the corresponding MFR with
  a modified Gauss-Newton method of least squares. <P />We apply the
  upgraded method to construct sigmoidal PECs for the 2009 February 13
  CME event. The resulting PECs have a complex core magnetic structure,
  with the MFR nested within a sheared magnetic arcade. Both the MFR and
  the arcade are bounded in the central region of the PECs by current
  layers. Depending on the strength of the current in the pre-relaxed
  MFR, the core of the final PEC can also contain a vertical current
  layer, which is then embedded in the sheared arcade, underneath the
  MFR. Our structural analysis reveals building blocks that match the
  morphological features typically observed in bipolar PECs (e.g., Moore
  et al., ApJ 2001) very well. This suggests that the method will not
  only be beneficial as a tool for modeling solar eruptions, but also for
  scientific studies that require a detailed understanding of the magnetic
  structure of PECs. <P />*Research supported by NSF, NASA, and AFOSR

---------------------------------------------------------
Title: Torus-Stable Zone Above Starspots
Authors: Sun, X.; Torok, T.; DeRosa, M.
2021AAS...23820801S    Altcode:
  The torus instability (TI) of current-carrying magnetic flux tubes
  is thought to drive many solar coronal mass ejections (CMEs). The
  background magnetic field provides the stabilizing force: if it
  decreases with height at a rate (decay index) slower than a critical
  value, the TI may be suppressed. Here we estimate the vertical extent
  of a "torus-stable zone" above starspots using a scaled model for the
  Sun. For a potential-field model comprising a bipole (as a pair of
  starspots) in alignment with a global dipole, we show that the upper
  bound of this zone h<SUB>c</SUB> increases with the bipole size a,
  the dipole field with harmonic coefficient g<SUB>10</SUB>, and the
  source surface radius R<SUB>s</SUB> where the magnetic field becomes
  radial. The value of h<SUB>c</SUB>, ranging from about 0.5a to a
  significant fraction of the stellar radius, depends on the interplay
  between the spot and dipole magnetic fields; its upper limit is set
  by R<SUB>s</SUB>. Suppression of the TI may contribute to the lack of
  CME detection from active cool stars, as larger starspots, stronger
  dipole, and more closed magnetic topology significantly expand the
  torus-stable zone.

---------------------------------------------------------
Title: Magnetic Field Curvature In A Filament Channel Derived From
    Oscillation Measurements And MHD Modeling
Authors: Kucera, T. A.; Luna, M.; Torok, T.; Muglach, K.; Downs, C.;
   Sun, X.; Thompson, B.; Karpen, J.; Gilbert, H.
2021AAS...23811306K    Altcode:
  We have used measurements of repeated large amplitude longitudinal
  oscillations (LALOs) in an active region filament to diagnose the
  curvature of the magnetic field in the filament channel and compared the
  results with predictions of an MHD flux-rope model based on magnetograms
  of the region. In May and June of 2014 Active Region 12076 exhibited a
  complex of filaments undergoing repeated oscillations over the course
  of twelve days. The central filament channel exhibited emerging and then
  canceling magnetic flux that resulted in multiple activations, filament
  eruptions, and eight oscillation events, which we analyzed using GONG
  H-alpha data. Luna and Karpen (2012) model LALOs as oscillations of
  magnetized filament plasma moving along dipped magnetic field lines
  with gravity as a restoring force. Under this model the period of these
  oscillations can be used to estimate the curvature of the magnetic
  field in the location of the filament threads. Utilizing this, we find
  that the measured periods in the central filament ranging from 34-74
  minutes should correspond to magnetic field curvatures of about 30-136
  Mm. We also derive radii of curvature for the central filament channel
  using a flux-rope model that is based on an SDO/HMI magnetogram of the
  region. The rope is constructed using the analytic expressions by Titov
  et al. (2018) and then numerically relaxed towards a force-free state in
  the zero-beta MHD approximation, where gravity and thermal pressure are
  neglected. For comparison, we also employ a nonlinear force-free field
  (NLFFF) extrapolation of the active region. We compare the results
  of these different ways of attempting to determine the field in the
  filament channel.

---------------------------------------------------------
Title: Torus-Stable Zone Above Starspots
Authors: Sun, Xudong; Török, Tibor; DeRosa, Marc
2021csss.confE..15S    Altcode:
  The torus instability (TI) of current-carrying magnetic flux tubes
  is thought to drive many solar coronal mass ejections (CMEs). The
  background magnetic field provides the stabilizing force: if it
  decreases with height at a rate slower than a critical value, the
  TI may be suppressed. Here we estimate the vertical extent of a
  "torus-stable zone" above starspots using a scaled model for the
  Sun. For a potential-field model comprising a bipole (as a pair of
  starspots) in alignment with a global dipole, we show that the upper
  bound of this zone h<SUB>c</SUB> increases with the bipole size a,
  the dipole field with harmonic coefficient g<SUB>10</SUB>, and the
  source surface radius R<SUB>s</SUB> where the magnetic field becomes
  radial. The value of h<SUB>c</SUB>, ranging from about 0.5a to a
  significant fraction of the stellar radius, depends on the interplay
  between the spot and dipole magnetic fields; its upper limit is set
  by R<SUB>s</SUB>. Suppression of the TI may contribute to the lack of
  CME detection from active cool stars, as larger starspots, stronger
  dipole, and more closed magnetic topology significantly expand the
  torus-stable zone.

---------------------------------------------------------
Title: Energetic Proton Propagation and Acceleration Simulated for
    the Bastille Day Event of 2000 July 14
Authors: Young, Matthew A.; Schwadron, Nathan A.; Gorby, Matthew;
   Linker, Jon; Caplan, Ronald M.; Downs, Cooper; Török, Tibor; Riley,
   Pete; Lionello, Roberto; Titov, Viacheslav; Mewaldt, Richard A.;
   Cohen, Christina M. S.
2021ApJ...909..160Y    Altcode: 2020arXiv201209078Y
  This work presents results from simulations of the 2000 July 14
  ("Bastille Day") solar proton event. We used the Energetic Particle
  Radiation Environment Model (EPREM) and the CORona-HELiosphere (CORHEL)
  software suite within the SPE Threat Assessment Tool (STAT) framework
  to model proton acceleration to GeV energies due to the passage of a
  CME through the low solar corona, and we compared the model results
  to GOES-08 observations. The coupled simulation models particle
  acceleration from 1 to 20 R<SUB>⊙</SUB>, after which it models only
  particle transport. The simulation roughly reproduces the peak event
  fluxes and the timing and spatial location of the energetic particle
  event. While peak fluxes and overall variation within the first few
  hours of the simulation agree well with observations, the modeled CME
  moves beyond the inner simulation boundary after several hours. The
  model therefore accurately describes the acceleration processes in
  the low corona and resolves the sites of most rapid acceleration close
  to the Sun. Plots of integral flux envelopes from multiple simulated
  observers near Earth further improve the comparison to observations
  and increase potential for predicting solar particle events. Broken
  power-law fits to fluence spectra agree with diffusive acceleration
  theory over the low energy range. Over the high energy range,
  they demonstrate the variability in acceleration rate and mirror
  the interevent variability observed in solar cycle 23 ground-level
  enhancements. We discuss ways to improve STAT predictions, including
  using corrected GOES energy bins and computing fits to the seed
  spectrum. This paper demonstrates a predictive tool for simulating
  low-coronal solar energetic particle acceleration.

---------------------------------------------------------
Title: Decay Index Profile and Coronal Mass Ejection Speed
Authors: Kliem, Bernhard; Zhang, Jie; Torok, Tibor; Chintzoglou,
   Georgios
2021cosp...43E.997K    Altcode:
  The velocity of coronal mass ejections (CMEs) is one of the primary
  parameters determining their potential geoeffectiveness. A great
  majority of very fast CMEs receive their main acceleration already
  in the corona. We study the magnetic source region structure for
  a complete sample of 15 very fast CMEs (v &gt; 1500 km/s) during
  2000--2006, originating within 30 deg from central meridian. We find
  a correlation between CME speed and the decay index profile of the
  coronal field estimated by a PFSS extrapolation. The correlation
  is considerably weaker for an extended sample that includes slower
  CMEs. We also study how the decay index profile is related to the
  structure of the photospheric field distribution. This is complemented
  by a parametric simulation study of flux-rope eruptions using the
  analytic Titov-D\'emoulin active-region model for simple bipolar and
  quadrupolar source regions. The simulations provide simple relationships
  between the photospheric field distribution and the coronal decay index
  profile. They also help identifying source regions which are likely to
  produce slow CMEs only, thus improving the correlation for the extended
  CME sample. Very fast, moderate-velocity, and even confined eruptions
  are found, and the conditions for their occurrence are quantified.

---------------------------------------------------------
Title: Optimization of Magnetic Flux Ropes Modeled with the RBSL
    Method*
Authors: Titov, V. S.; Downs, C.; Torok, T.; Linker, J.; Caplan,
   R. M.; Lionello, R.
2020AGUFMSH0440022T    Altcode:
  The so-called regularized Biot-Savart laws (RBSLs, Titov et al. 2018)
  provide an efficient and flexible method for modeling pre-eruptive
  magnetic configurations whose characteristics are constrained by
  observational image and magnetic-field data. This method allows
  one to calculate the field of magnetic flux ropes (MFRs) with small
  circular cross-sections and an arbitrary axis shape. The field of
  the whole configuration is constructed as a superposition of (1)
  such a flux-rope field, (2) an ambient potential field determined,
  for example, by the radial field component of an observed magnetogram,
  and (3) a so-called compensating potential field that counteracts
  deviations of the radial field caused by the axial current of the
  MFR. The RBSL kernels are determined from the requirement that the MFR
  field for a straight cylinder must be exactly force-free. For a curved
  MFR, however, the magnetic forces are generally unbalanced over the
  whole path of the MFR. To reduce this imbalance, we apply a modified
  Gauss-Newton method to minimize the magnitude of the residual magnetic
  forces per unit length and the unit axial current of the MFR. This is
  done by iteratively adjusting the MFR axis path and axial current. We
  then try to relax the resulting optimized configuration in a subsequent
  line-tied zero-beta MHD simulation toward a force-free equilibrium. By
  considering several examples, we demonstrate how this approach works
  depending on the initial parameters of the MFR and the ambient magnetic
  field. Our method will be beneficial for both the modeling of particular
  eruptive events and theoretical studies of idealized pre-eruptive
  magnetic configurations. <P />* This research is supported by NSF,
  NASA's HSR, SBIR, and LWS Programs, and AFOSR

---------------------------------------------------------
Title: Solar and Heliospheric Models at the CCMC - An Update
Authors: MacNeice, P. J.; Chulaki, A.; Mendoza, A. M. M.; Mays, M. L.;
   Weigand, C.; Arge, C. N.; Jones, S. I.; Linker, J.; Downs, C.; Torok,
   T.; Fisher, G. H.; Cheung, C. M. M.
2020AGUFMSH0030015M    Altcode:
  The Community Coordinated Modeling Center (CCMC) at NASA Goddard Space
  Flight Center is the world largest repository of models dedicated to
  Space Weather Research and forecasting. In this presentation we provide
  an update on new additions and updates to the CCMC's inventory of Solar
  and Heliospheric models. In particular, we describe the latest version
  of WSA, the CORHEL TDM model, and the CGEM model suite. The latest
  version of WSA is now available to users through our Runs-On-Request
  websites as well as through its continuous near realtime execution. It
  can use input magnetograms from an extensive list of observatories,
  including maps processed using the ADAPT surface flux evolution
  model, and can return results and solar wind forecasts at all inner
  planets and most inner heliospheric spacecraft locations. The CORHEL
  TDM model enables users to design flux ropes embedded in coronal
  fields in derived from observed magnetograms, and then follow the
  evolution of the flux rope using a zero-beta MHD code. A future upgrade
  (currently in development at PredSci) w ill support full thermodynamic
  CME simulations. Finally, the CGEM model suite supports the generation
  and application of boundary conditions for realistic driving of coronal
  3D field models based on times series observations of photospheric
  vector magnetogram data.

---------------------------------------------------------
Title: Coronal Acceleration of Large and Acute SEP Events
Authors: Young, M.; Schwadron, N.; Gorby, M.; Linker, J.; Caplan,
   R. M.; Downs, C.; Torok, T.; Riley, P.; Lionello, R.; Titov, V. S.;
   Mewaldt, R.; Cohen, C.
2020AGUFMSH012..03Y    Altcode:
  Solar energetic particle (SEP) events pose a serious threat to
  spacecraft and astronauts throughout the heliosphere. On Earth, strong
  events can harm aircraft avionics, communication, and navigation. In
  space, energetic particles can be hazardous for crews of Low Earth Orbit
  spacecraft and the International Space Station, especially when engaged
  in extravehicular activity. One important goal when studying energetic
  particles in the heliosphere is providing a meaningful estimate of
  their flux at a the location of a particular observer. At Earth,
  good estimates of both the energetic particle flux and the expected
  intra-event variability can significantly improve our ability to protect
  space-based assets without incurring unnecessary operational delays. The
  largest SEP events typically arise in conjunction with X-class flares
  and very fast coronal mass ejections (CMEs). One probable mechanism for
  accelerating energetic particles that propagate to Earth is the shock
  wave or compression that forms low in the corona during the passage of
  a CME. After the shock wave or compression forms, it propagates outward
  and accelerates particles over a finite space for a finite time. These
  energetic particles can travel at a significant fraction of the speed of
  light and reach an observer soon after an eruptive event if the observer
  and the acceleration site are magnetically connected. This connectivity
  depends, in turn, on both the structure of the coronal and heliospheric
  magnetic field and the local shock properties. Furthermore, intra-event
  variability depends on local properties (e.g., mean free path and
  rigidity) along the field line where the shock wave or compression
  accelerates particles, and the finite scales over which the shock wave
  or compression operates. This work presents results from a simulation
  of the extreme SEP event on 14 July (Bastille Day) 2000, using the
  Energetic Particle Radiation Environment Model (EPREM) coupled to
  the Magnetohydrodynamic Algorithm outside a Sphere (MAS) code from
  Predictive Science Incorporated (PSI). We show how coronal variability
  in acceleration rate and compression strength maps to variability at
  1 au, with a focus on field lines connected to near-Earth observers,
  and how this intra-event variability compares to observed inter-event
  variability in GOES data.

---------------------------------------------------------
Title: Partially Open Fields and the Energy of Solar Eruptions
Authors: Linker, J.; Downs, C.; Caplan, R. M.; Torok, T.; Kazachenko,
   M.; Titov, V. S.; Lionello, R.; Riley, P.
2020AGUFMSH046..01L    Altcode:
  It has long been recognized that the energy source for major solar
  flares and coronal mass ejections (CMEs) is the solar magnetic field
  within active regions. Specifically, it is believed to be the release
  of the free magnetic energy (energy above the potential field state)
  stored in the field prior to eruption. For estimates of the free energy
  to provide a prognostic for future eruptions, we must know how much
  energy an active region can store - Is there a bound to this energy? <P
  />The Aly-Sturrock theorem shows that the energy of a fully force-free
  field cannot exceed the energy of the so-called open field. If the
  theorem holds, this places an upper limit on the amount of free energy
  that can be stored. In recent simulations, we have found that the energy
  of a closely related field, the partially open field (POF), can place
  a useful bound on the energy of an eruption from real active regions,
  a much tighter constraint than the energy of the fully open field. A
  database of flare ribbons (Kazachenko et al., ApJ 845, 2017) offers us
  an opportunity to test this idea observationally. A flare ribbon mask
  is defined as the area swept out by the ribbons during the flare. It
  can serve as a proxy for the region of the field that opened during
  the eruption. In this preliminary study, we use the ribbon masks to
  define the POF for several large events originating in solar cycle 24
  active regions, and compute the energy of the POF. We compare these
  energies with the X-ray fluxes and CME energies for these events. <P
  />Work supported by NSF, NASA, and AFOSR.

---------------------------------------------------------
Title: MHD Modeling of an Observed Solar Filament
Authors: Torok, T.; Downs, C.; Titov, V. S.; Lionello, R.; Linker, J.
2020AGUFMSH041..04T    Altcode:
  The physical mechanisms by which solar prominences (or filaments) form
  are still not well understood. The presently most favored scenario
  invokes the evaporation of chromospheric plasma via localized heating
  at the footprints of a magnetic flux rope (MFR) or sheared arcade, and
  the subsequent condensation of this plasma in the corona due to thermal
  non-equilibrium (TNE). This scenario has been modeled extensively in
  one-dimensional (1D) hydrodynamic simulations along static magnetic
  field lines and, very recently, also in fully 3D magnetohydrodynamic
  (MHD) simulations, using idealized MFR configurations. However, such
  configurations lack the complexity of real prominence magnetic fields,
  which poses additional challenges. Here we report on our recent attempts
  to employ data-constrained MHD simulations to model the formation of
  observed filaments. To this end, we selected the filament that erupted
  in a spectacular manner on June 7, 2011 in NOAA AR 11226. To model its
  formation, we first develop a semi-realistic ("thermodynamic MHD") model
  of the solar corona, using SDO/HMI data as boundary condition for the
  magnetic field. Next, we insert an MFR constructed with the RBSL method
  (Titov et al., 2018) into the source region of the filament. Finally,
  after a short relaxation of the system, we impose localized heating in
  the footprint regions of the MFR. In our study, we vary the geometry
  and footprint locations of the MFR, as well as the amount of heating
  in the respective MFR footprints, and investigate how these parameters
  affect the formation of persistent plasma condensations. We compare
  our results with simulations of prominence formation in idealized
  MFR configurations, and we discuss the difficulties that arise once
  realistic cases are considered.

---------------------------------------------------------
Title: Decoding the Pre-Eruptive Magnetic Field Configurations of
    Coronal Mass Ejections
Authors: Patsourakos, S.; Vourlidas, A.; Török, T.; Kliem, B.;
   Antiochos, S. K.; Archontis, V.; Aulanier, G.; Cheng, X.; Chintzoglou,
   G.; Georgoulis, M. K.; Green, L. M.; Leake, J. E.; Moore, R.; Nindos,
   A.; Syntelis, P.; Yardley, S. L.; Yurchyshyn, V.; Zhang, J.
2020SSRv..216..131P    Altcode: 2020arXiv201010186P
  A clear understanding of the nature of the pre-eruptive magnetic
  field configurations of Coronal Mass Ejections (CMEs) is required
  for understanding and eventually predicting solar eruptions. Only
  two, but seemingly disparate, magnetic configurations are considered
  viable; namely, sheared magnetic arcades (SMA) and magnetic flux ropes
  (MFR). They can form via three physical mechanisms (flux emergence,
  flux cancellation, helicity condensation). Whether the CME culprit
  is an SMA or an MFR, however, has been strongly debated for thirty
  years. We formed an International Space Science Institute (ISSI) team to
  address and resolve this issue and report the outcome here. We review
  the status of the field across modeling and observations, identify
  the open and closed issues, compile lists of SMA and MFR observables
  to be tested against observations and outline research activities
  to close the gaps in our current understanding. We propose that the
  combination of multi-viewpoint multi-thermal coronal observations
  and multi-height vector magnetic field measurements is the optimal
  approach for resolving the issue conclusively. We demonstrate the
  approach using MHD simulations and synthetic coronal images.

---------------------------------------------------------
Title: Electric-current Neutralization and Eruptive Activity of
    Solar Active Regions
Authors: Torok, Tibor; Liu, Yang; Leake, James E.; Sun, Xudong; Titov,
   Viacheslav S.
2020EGUGA..22.1654T    Altcode:
  The physical conditions that determine the eruptive activity of
  solar active regions (ARs) are still not well understood. Various
  proxies for predicting eruptive activity have been suggested, with
  relatively limited success. Moreover, it is presently unclear under
  which conditions an eruption will remain confined to the low corona
  or produce a coronal mass ejection (CME).Using vector magnetogram data
  from SDO/HMI, we investigate the association between electric-current
  neutralization and eruptive activity for a sample of ARs. We find
  that the vast majority of CME-producing ARs are characterized by a
  strongly non-neutralized total current, while the total current in
  ARs that do not produce CMEs is almost perfectly neutralized, even
  if those ARs produce strong (X-class) confined flares. This suggests
  that the degree of current neutralization can serve as a good proxy
  for assessing the ability of ARs to produce CMEs.

---------------------------------------------------------
Title: Initiation and Early Kinematic Evolution of Solar Eruptions
Authors: Cheng, X.; Zhang, J.; Kliem, B.; Török, T.; Xing, C.;
   Zhou, Z. J.; Inhester, B.; Ding, M. D.
2020ApJ...894...85C    Altcode: 2020arXiv200403790C
  We investigate the initiation and early evolution of 12 solar eruptions,
  including six active-region hot channel and six quiescent filament
  eruptions, which were well observed by the Solar Dynamics Observatory,
  as well as by the Solar Terrestrial Relations Observatory for the
  latter. The sample includes one failed eruption and 11 coronal mass
  ejections, with velocities ranging from 493 to 2140 km s<SUP>-1</SUP>. A
  detailed analysis of the eruption kinematics yields the following main
  results. (1) The early evolution of all events consists of a slow-rise
  phase followed by a main-acceleration phase, the height-time profiles
  of which differ markedly and can be best fit, respectively, by a linear
  and an exponential function. This indicates that different physical
  processes dominate in these phases, which is at variance with models
  that involve a single process. (2) The kinematic evolution of the
  eruptions tends to be synchronized with the flare light curve in both
  phases. The synchronization is often but not always close. A delayed
  onset of the impulsive flare phase is found in the majority of the
  filament eruptions (five out of six). This delay and its trend to be
  larger for slower eruptions favor ideal MHD instability models. (3)
  The average decay index at the onset heights of the main acceleration
  is close to the threshold of the torus instability for both groups
  of events (although, it is based on a tentative coronal field model
  for the hot channels), suggesting that this instability initiates and
  possibly drives the main acceleration.

---------------------------------------------------------
Title: Prediction of Coronal Structure for the July 2, 2019 Total
Solar Eclipse: Comparison with Observations
Authors: Linker, J.; Downs, C.; Caplan, R. M.; Riley, P.; Titov,
   V. S.; Lionello, R.; Torok, T.; Reyes, A.
2019AGUFMSH13A..04L    Altcode:
  We are fortunate to study the Sun at a time when so many space-based
  assets observe the Sun and its corona remotely, as well as measuring
  the solar wind (the interplanetary extension of the corona) in
  situ. Yet even at this time, total solar eclipses offer an unparalleled
  opportunity to observe the low and middle corona. These observations
  in turn are a powerful test of coronal models. As is our tradition,
  we used our global thermodynamic magnetohydrodynamic (MHD) model
  to predict the structure of the solar corona prior to the July 2,
  2019 total solar eclipse. The key observational input to the model are
  measurements of the photospheric magnetic field. The model incorporates
  a wave-turbulence driven (WTD) description of coronal heating and solar
  wind acceleration, and shear/twist in the magnetic field at the observed
  location of filament channels. We compare our prediction with available
  eclipse images, and with SDO/AIA and STEREO EUVI data. A particular
  emphasis in this prediction was the inclusion of parasitic polarities
  in the polar regions, as this creates plume-like structures in the
  simulated corona. Significant plumes were indeed observed, which we
  compare with the modeled structures. <P />Research supported by NASA,
  AFOSR, and NSF.

---------------------------------------------------------
Title: Modeling Magnetic Flux Ropes with the RBSL Method
Authors: Titov, V. S.; Downs, C.; Torok, T.; Caplan, R. M.; Linker,
   J.; Lionello, R.; Reyes, A.
2019AGUFMSH33B3386T    Altcode:
  We describe progress in developing a method for smoothly embedding
  magnetic flux ropes (MFRs) with various internal structures into ambient
  potential magnetic fields. The method uses the so-called regularized
  Biot-Savart laws (RBSLs, Titov et al. 2018), which enable one to
  calculate the magnetic field produced by axial and azimuthal currents
  flowing in a channel with a circular cross-section and an axis path
  of arbitrary shape. In the latest version of our method, the whole
  configuration is a superposition of the following three fields: 1)
  the MFR field determined by the RBSLs, 2) an ambient potential field
  determined, for example, by the radial field component of an observed
  magnetogram, and 3) a so-called compensating potential field that
  counteracts perturbations of the radial field at the surface by the
  MFR field. To make the configuration as force-free as possible, the
  method aims to optimize the MFR characteristics in two ways. First,
  for a cylindrical force-free MFR, we determine the corresponding
  kernels of the RBSLs for different profiles of the axial current
  density and use those to calculate the magnetic field of a thin,
  curved MFR, which has slightly imbalanced magnetic forces. Second, we
  minimize this imbalance by iteratively adjusting the shape of the MFR,
  based on the line density of magnetic forces that we calculate along
  the MFR at every iteration. If the resulting optimized MFR is stable,
  a subsequent line-tied zero-beta MHD relaxation will typically yield
  a force-free MFR whose parameters are quite close to the initial
  ones. MFR configurations produced in this way should be very useful
  for modeling solar eruptions, because the initial MFR parameters are
  largely determined by the specific properties of the source-region. Our
  efficient method also facilitates parametric studies and the stability
  analysis of pre-eruptive configurations. We demonstrate this by using an
  idealized model of a toroidal-arc MFR, for which we derive the critical
  decay index of its ambient field as a function of the MFR parameters.

---------------------------------------------------------
Title: Exploring Plasma Heating in the Current Sheet Region in a
    Three-dimensional Coronal Mass Ejection Simulation
Authors: Reeves, Katharine K.; Török, Tibor; Mikić, Zoran; Linker,
   Jon; Murphy, Nicholas A.
2019ApJ...887..103R    Altcode: 2019arXiv191005386R
  We simulate a coronal mass ejection using a three-dimensional
  magnetohydrodynamic code that includes coronal heating, thermal
  conduction, and radiative cooling in the energy equation. The magnetic
  flux distribution at 1 R <SUB> s </SUB> is produced by a localized
  subsurface dipole superimposed on a global dipole field, mimicking
  the presence of an active region within the global corona. Transverse
  electric fields are applied near the polarity inversion line to
  introduce a transverse magnetic field, followed by the imposition of
  a converging flow to form and destabilize a flux rope, producing an
  eruption. We examine the quantities responsible for plasma heating and
  cooling during the eruption, including thermal conduction, radiation,
  adiabatic effects, coronal heating, and ohmic heating. We find that
  ohmic heating is an important contributor to hot temperatures in the
  current sheet region early in the eruption, but in the late phase,
  adiabatic compression plays an important role in heating the plasma
  there. Thermal conduction also plays an important role in the transport
  of thermal energy away from the current sheet region throughout the
  reconnection process, producing a “thermal halo” and widening the
  region of high temperatures. We simulate emission from solar telescopes
  for this eruption and find that there is evidence for emission from
  heated plasma above the flare loops late in the eruption, when the
  adiabatic heating is the dominant heating term. These results provide an
  explanation for hot supra-arcade plasma sheets that are often observed
  in X-rays and extreme ultraviolet wavelengths during the decay phase
  of large flares.

---------------------------------------------------------
Title: Solar Eruptions Triggered by Flux Emergence
Authors: Torok, T.; Linton, M.; Leake, J. E.; Mikic, Z.; Titov, V. S.;
   Lionello, R.
2019AGUFMSH33B3390T    Altcode:
  Observations have shown a clear association of prominence eruptions
  and CMEs with the emergence of magnetic flux close to, or within,
  filament channels. It has been suggested that reconnection triggered
  by the emergence destroys the force balance between the magnetic
  field in the filament channel and its ambient field, causing the
  former to erupt. Magnetohydrodynamic (MHD) numerical simulations
  support this scenario for two-dimensional (2D) coronal flux-rope
  configurations. However, such simulations do not take into account 3D
  effects such as the anchoring of the flux rope in the dense photosphere
  or the occurrence of 3D MHD instabilities. Here we present the first
  3D MHD simulations of (boundary-driven) flux emergence in the vicinity
  of a pre-existing coronal flux rope. We find that three processes
  are important for the evolution of the system: (1) expansion or
  contraction of the coronal field due to the intrusion of new flux,
  (2) reconnection between the emerging and pre-existing flux systems,
  and (3) repulsion or attraction of the respective current channels. We
  vary the position and orientation of the emerging flux and investigate
  under which conditions these processes can trigger an eruption.

---------------------------------------------------------
Title: Data-Constrained Modeling of Eruptions in the Solar Corona:
    Insights from 3D MHD Simulations
Authors: Downs, C.; Torok, T.; Titov, V. S.; Linker, J.
2019AGUFMSH32A..06D    Altcode:
  Understanding the energy storage and release processes of solar
  eruptions, also known as Coronal Mass Ejections (CMEs), remains
  challenging on multiple fronts. On one hand, the complexity of solar
  active regions, and the myriad ways in which they present themselves,
  makes it difficult to pin down the essential mechanisms of CMEs. On
  the other hand, our primary way of observing the early stages of CMEs
  is through remote sensing diagnostics, which provide only partial
  inferences of the underlying plasma state. Sophisticated models that
  capture both the energy storage and release processes in tandem with
  remote sensing diagnostics are one way to approach this problem. Using
  these ideas to frame our discussion, we present an overview of the
  essential steps for constructing a case-study, data-constrained model of
  a solar eruption using a 3D thermodynamic MHD model of the global solar
  corona. Choices for boundary conditions, energy storage, initiation,
  and the global coronal background all have significant consequences
  for the ensuing evolution and interpretation of results. Despite these
  complexities and challenges, we show how such modeling can be used
  to directly connect the observable consequences of CMEs (EUV waves,
  coronal dimming) to their underlying physical processes (CME expansion
  and connectivity changes). Such modeling helps to unify our picture of
  CMEs as they evolve and interact with disparate regions of the solar
  atmosphere. Future prospects will also be discussed.

---------------------------------------------------------
Title: Stabilities of magnetic flux ropes anchored in the solar
    surface
Authors: Qiu, J.; Downs, C.; Titov, V. S.; Torok, T.
2019AGUFMSH33B3391Q    Altcode:
  Eruptions of a magnetic flux rope in the solar corona can be
  triggered by certain magnetohydrodynamic (MHD) instabilities, such
  as the helical <P />kink instability or the torus instability. The
  instability threshold depends on the geometry of the flux rope, and
  it is not a-priori clear which instability will occur or dominate in a
  given configuration. Furthermore, a magnetic flux rope is anchored in
  the photosphere, and this line-tying condition imposes an essential
  constraint on the stability analysis. The modified Titov-Demoulin
  model (TDm, Titov et al. 2014) provides a three-parameter family of
  approximate equilibria of a toroidal-arc magnetic flux rope anchored
  in the photosphere that is smoothly embedded in an ambient bipolar
  potential field in a spherical geometry. This study examines the
  stability of a force-free TDm magnetic flux rope in dependence of its
  geometric parameters. The global MHD MAS code is used to evolve the
  flux ropes under the line-tying condition. For a given perturbation of
  the flux rope, a configuration is not stable if it never returns to
  an equilibrium or if it evolves into a new equilibrium that deviates
  strongly from the initial equilibrium solution. Our preliminary study
  suggests that configurations with an X-line below the flux rope are
  usually not stable, and also confirms that a high-lying flux rope can
  be kink-stable even for large twist (see, e.g., Torok et al. 2004).

---------------------------------------------------------
Title: Formation and Eruption of Magnetic Flux Ropes in the Solar
    Corona
Authors: Linton, Mark; Torok, Tibor; Leake, James
2019AAS...23430201L    Altcode:
  Magnetic flux ropes in the solar corona are often thought to form
  the basis for both long-lived coronal prominences and for eruptive
  coronal mass ejections. In this presentation we discuss numerical
  simulations exploring how such flux rope structures can both be created
  and disrupted via the emergence of magnetic flux from the convection
  zone into the corona. The presentation will focus on the formation of
  these structures directly from flux emergence as well as the effects,
  both stabilizing and eruptive, that newly emerging flux can have on
  pre-existing coronal flux ropes. <P />This work is supported by the
  NASA Living with a Star program and the Chief of Naval Research.

---------------------------------------------------------
Title: Bounding the Energy of Solar Eruptions
Authors: Linker, Jon A.; Downs, Cooper; Caplan, Ronald M.; Torok,
   Tibor; Riley, Pete; Titov, Viacheslav; Lionello, Roberto; Mikic,
   Zoran; Amari, Tahar
2019AAS...23431704L    Altcode:
  Major solar eruptions such as X-class flares and coronal mass ejections
  (CMEs) are the fundamental source of solar energetic particles and
  geomagnetic storms, and are thus key drivers of space weather at
  Earth. The energy for solar eruptions is recognized to originate in
  the solar magnetic field, and is believed to be stored as free magnetic
  energy (energy above the potential field state) prior to eruption. Solar
  active regions are the site of the most violent activity. Solar active
  regions can store widely varying amounts of energy, so knowledge of
  the free energy alone does not necessarily tell us when an eruption
  is imminent. For estimates of the free energy to provide predictive
  power, we must know how much energy a region can store - what is the
  energy bound? <P />In recent work, we have found that the energy of a
  particular field, the partially open field (POF), can place a useful
  bound on the energy of an eruption from real active regions, a much
  tighter constraint than the energy of the fully open field. However,
  in general, it is difficult to solve for the POF. In this presentation,
  we discuss methods for approximating the energy of this field, and
  show a comparison of the approximation for a case where the solution
  is known. We discuss the implications for understanding and predicting
  major solar eruptions. <P />Research supported by NASA and AFOSR

---------------------------------------------------------
Title: Coupled MHD-Focused Transport Simulations for Modeling Solar
    Particle Events
Authors: Linker, Jon A.; Caplan, Ronald M.; Schwadron, Nathan;
   Gorby, Matthew; Downs, Cooper; Torok, Tibor; Lionello, Roberto;
   Wijaya, Janvier
2019JPhCS1225a2007L    Altcode: 2019arXiv190505299L
  We describe the initial version of the Solar Particle Event (SPE) Threat
  Assessment Tool or STAT. STAT relies on elements of Corona-Heliosphere
  (CORHEL) and the Earth-Moon-Mars Radiation Environment Module (EMMREM),
  and allows users to investigate coronal mass ejection (CME) driven
  SPEs using coupled magnetohydrodynamic (MHD) and focused transport
  solutions. At the present time STAT focuses on modeling solar energetic
  particle (SEP) acceleration in and transport from the low corona,
  where the highest energy SEP events are generated. We illustrate
  STAT’s capabilities with a model of the July 14, 2000 “Bastille
  Day” event, including innovative diagnostics for understanding the
  three-dimensional distribution of particle fluxes and their relation
  to the structure of the underlying CME driver. A preliminary comparison
  with NOAA GOES measurements is shown.

---------------------------------------------------------
Title: Sheared Magnetic Arcades and the Pre-eruptive Magnetic
Configuration of Coronal Mass Ejections: Diagnostics, Challenges
    and Future Observables
Authors: Patsourakos, Spiros; Vourlidas, A.; Anthiochos, S. K.;
   Archontis, V.; Aulanier, G.; Cheng, X.; Chintzoglou, G.; Georgoulis,
   M. K.; Green, L. M.; Kliem, B.; Leake, J.; Moore, R. L.; Nindos, A.;
   Syntelis, P.; Torok, T.; Yardley, S. L.; Yurchyshyn, V.; Zhang, J.
2019shin.confE.194P    Altcode:
  Our thinking about the pre-eruptive magnetic configuration of Coronal
  Mass Ejections has been effectively dichotomized into two opposing
  and often fiercely contested views: namely, sheared magnetic arcades
  and magnetic flux ropes. Finding a solution to this issue will have
  important implications for our understanding of CME initiation. We
  first discuss the very value of embarking into the arcade vs. flux rope
  dilemma and illustrate the corresponding challenges and difficulties to
  address it. Next, we are compiling several observational diagnostics of
  pre-eruptive sheared magnetic arcades stemming from theory/modeling,
  discuss their merits, and highlight potential ambiguities that could
  arise in their interpretation. We finally conclude with a discussion
  of possible new observables, in the frame of upcoming or proposed
  instrumentation, that could help to circumvent the issues we are
  currently facing.

---------------------------------------------------------
Title: GPU Acceleration of an Established Solar MHD Code using OpenACC
Authors: Caplan, R. M.; Linker, J. A.; Mikić, Z.; Downs, C.; Török,
   T.; Titov, V. S.
2019JPhCS1225a2012C    Altcode: 2018arXiv181102605C
  GPU accelerators have had a notable impact on high-performance
  computing across many disciplines. They provide high performance with
  low cost/power, and therefore have become a primary compute resource
  on many of the largest supercomputers. Here, we implement multi-GPU
  acceleration into our Solar MHD code (MAS) using OpenACC in a fully
  portable, single-source manner. Our preliminary implementation is
  focused on MAS running in a reduced physics “zero-beta” mode. While
  valuable on its own, our main goal is to pave the way for a full
  physics, thermodynamic MHD implementation. We describe the OpenACC
  implementation methodology and challenges. “Time-to-solution”
  performance results of a production-level flux rope eruption
  simulation on multi-CPU and multi-GPU systems are shown. We find that
  the GPU-accelerated MAS code has the ability to run “zero-beta”
  simulations on a single multi-GPU server at speeds previously requiring
  multiple CPU server-nodes of a supercomputer.

---------------------------------------------------------
Title: What is the pre-eruptive structure of CMEs?
Authors: Torok, Tibor
2019shin.confE..45T    Altcode:
  Coronal mass ejections (CMEs) are, together with major flares,
  the largest energy-release processes in the solar system and the
  main driver of space-weather disturbances close to the Earth. While
  CMEs have been studied for almost half a century, many open questions
  remain, especially regarding their initiation and pre-eruptive magnetic
  structure. There is little doubt that CMEs are organized as flux ropes,
  but there still exists a heated debate on whether the flux rope exits
  prior to the eruption or is formed (from a sheared arcade) during the
  eruption process. In this talk I will review the main arguments in favor
  of the flux-rope picture, and I will argue that our current perspective
  of 'either flux rope or arcade' is too simplistic and should be revised.

---------------------------------------------------------
Title: Prediction of Coronal Structure for the July 2, 2019 Total
    Solar Eclipse
Authors: Linker, Jon A.; Downs, C.; Caplan, R. M.; Riley, P.; Lionello,
   R.; Titov, V. S.; Torok, T.; Reyes, A.
2019shin.confE..66L    Altcode:
  We are fortunate to study the Sun at a time when so many space-based
  assets observe the Sun and its corona remotely, as well as measuring
  the solar wind (the interplanetary extension of the corona) in
  situ. Yet even at this time, total solar eclipses offer an unparalleled
  opportunity to observe the low and middle corona. These observations
  in turn are a powerful test of coronal models. As is our tradition,
  we are predicting the structure of the solar corona for the July 2,
  2019 total solar eclipse. We describe progress and challenges in
  modeling the global thermodynamic and magnetic state of the solar
  corona for the prediction. The key observational input to the model are
  measurements of the photospheric magnetic field. The model incorporates
  a wave-turbulence driven (WTD) description of coronal heating and solar
  wind acceleration, and shear/twist in the field at the expected location
  of filament channels. The prediction will include images of brightness,
  polarization brightness, EUV, and X-rays. We describe comparisons of
  our prediction with available ground-based observations of the eclipse,
  as well as observations from SDO/AIA, Hinode/XRT, and STEREO/EUVI. <P
  />Research supported by NASA, AFOSR, and NSF.

---------------------------------------------------------
Title: Particle Radiation Sources, Propagation and Interactions
in Deep Space, at Earth, the Moon, Mars, and Beyond: Examples of
    Radiation Interactions and Effects
Authors: Schwadron, Nathan A.; Cooper, John F.; Desai, Mihir; Downs,
   Cooper; Gorby, Matt; Jordan, Andrew P.; Joyce, Colin J.; Kozarev,
   Kamen; Linker, Jon A.; Mikíc, Zoran; Riley, Pete; Spence, Harlan E.;
   Török, Tibor; Townsend, Lawrence W.; Wilson, Jody K.; Zeitlin, Cary
2019sfsw.book..257S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The Physical Processes of CME/ICME Evolution
Authors: Manchester, Ward, IV; Kilpua, Emilia K. J.; Liu, Ying D.;
   Lugaz, Noé; Riley, Pete; Török, Tibor; Vršnak, Bojan
2019sfsw.book..165M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The Origin, Early Evolution and Predictability of Solar
    Eruptions
Authors: Green, Lucie M.; Török, Tibor; Vršnak, Bojan; Manchester,
   Ward, IV; Veronig, Astrid
2019sfsw.book..113G    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Electric-current Neutralization and Eruptive Activity of
    Solar Active Regions
Authors: Liu, Yang; Sun, Xudong; Torok, Tibor; Titov, Viacheslav S.;
   Leake, James E.
2018csc..confE..39L    Altcode:
  The physical conditions that determine the eruptive activity of active
  regions (ARs) are still not well understood. Various observational
  proxies for predicting eruptive activity have been suggested, with
  rather limited success. Moreover, it is presently unclear under which
  conditions an eruption will remain confined to the low corona or
  produce a coronal mass ejection (CME). Using vector magnetogram data
  from SDO/HMI, we investigate the association between electric-current
  neutralization and eruptive activity for four ARs. Two ARs produced
  flares and CMEs, one produced only (very strong) confined flares,
  and one did not exhibit significant eruptions. We find that both
  CME-producing ARs are characterized by a strongly non-neutralized
  total current, while the total current in the remaining ARs is almost
  perfectly neutralized. This suggests that the degree of current
  neutralization may serve as a proxy for assessing the ability of ARs
  to produce CMEs.

---------------------------------------------------------
Title: Global Non-Potential Magnetic Models of the Solar Corona
    During the March 2015 Eclipse
Authors: Yeates, Anthony R.; Amari, Tahar; Contopoulos, Ioannis; Feng,
   Xueshang; Mackay, Duncan H.; Mikić, Zoran; Wiegelmann, Thomas; Hutton,
   Joseph; Lowder, Christopher A.; Morgan, Huw; Petrie, Gordon; Rachmeler,
   Laurel A.; Upton, Lisa A.; Canou, Aurelien; Chopin, Pierre; Downs,
   Cooper; Druckmüller, Miloslav; Linker, Jon A.; Seaton, Daniel B.;
   Török, Tibor
2018SSRv..214...99Y    Altcode: 2018arXiv180800785Y
  Seven different models are applied to the same problem of simulating
  the Sun's coronal magnetic field during the solar eclipse on 2015
  March 20. All of the models are non-potential, allowing for free
  magnetic energy, but the associated electric currents are developed
  in significantly different ways. This is not a direct comparison
  of the coronal modelling techniques, in that the different models
  also use different photospheric boundary conditions, reflecting
  the range of approaches currently used in the community. Despite
  the significant differences, the results show broad agreement in the
  overall magnetic topology. Among those models with significant volume
  currents in much of the corona, there is general agreement that the
  ratio of total to potential magnetic energy should be approximately
  1.4. However, there are significant differences in the electric current
  distributions; while static extrapolations are best able to reproduce
  active regions, they are unable to recover sheared magnetic fields in
  filament channels using currently available vector magnetogram data. By
  contrast, time-evolving simulations can recover the filament channel
  fields at the expense of not matching the observed vector magnetic
  fields within active regions. We suggest that, at present, the best
  approach may be a hybrid model using static extrapolations but with
  additional energization informed by simplified evolution models. This
  is demonstrated by one of the models.

---------------------------------------------------------
Title: Sequential Eruptions Triggered by Flux Emergence: Observations
    and Modeling
Authors: Dacie, S.; Török, T.; Démoulin, P.; Linton, M. G.; Downs,
   C.; van Driel-Gesztelyi, L.; Long, D. M.; Leake, J. E.
2018ApJ...862..117D    Altcode: 2018arXiv180700020D
  We describe and analyze observations by the Solar Dynamics Observatory
  of the emergence of a small, bipolar active region within an area of
  unipolar magnetic flux that was surrounded by a circular, quiescent
  filament. Within only 8 hours from the start of the emergence, a
  partial splitting of the filament and two consecutive coronal mass
  ejections took place. We argue that all three dynamic events occurred
  as a result of particular magnetic-reconnection episodes between
  the emerging bipole and the pre-existing coronal magnetic field. To
  substantiate our interpretation, we consider 3D magnetohydrodynamic
  simulations that model the emergence of magnetic flux in the vicinity of
  a large-scale coronal flux rope. The simulations qualitatively reproduce
  most of the reconnection episodes suggested by the observations, as
  well as the filament splitting, the first eruption, and the formation
  of sheared/twisted fields that may have played a role in the second
  eruption. Our results suggest that the position of emerging flux with
  respect to the background magnetic configuration is a crucial factor for
  the resulting evolution, while previous results suggest that parameters
  such as the orientation or the amount of emerging flux are important
  as well. This poses a challenge for predicting the onset of eruptions
  that are triggered by flux emergence, and calls for a detailed survey
  of the relevant parameter space by means of numerical simulations.

---------------------------------------------------------
Title: Predicting the corona for the 21 August 2017 total solar
    eclipse
Authors: Mikić; , Zoran; Downs, Cooper; Linker, Jon A.; Caplan, Ronald
   M.; Mackay, Duncan H.; Upton, Lisa A.; Riley, Pete; Lionello, Roberto;
   Török, Tibor; Titov, Viacheslav S.; Wijaya, Janvier; Druckmüller,
   Miloslav; Pasachoff, Jay M.; Carlos, Wendy
2018NatAs...2..913M    Altcode: 2018NatAs.tmp..120M
  The total solar eclipse that occurred on 21 August 2017 across the
  United States provided an opportunity to test a magnetohydrodynamic
  model of the solar corona driven by measured magnetic fields. We used
  a new heating model based on the dissipation of Alfvén waves, and
  a new energization mechanism to twist the magnetic field in filament
  channels. We predicted what the corona would look like one week before
  the eclipse. Here, we describe how this prediction was accomplished,
  and show that it compared favourably with observations of the
  eclipse in white light and extreme ultraviolet. The model allows us to
  understand the relationship of observed features, including streamers,
  coronal holes, prominences, polar plumes and thin rays, to the magnetic
  field. We show that the discrepancies between the model and observations
  arise from limitations in our ability to observe the Sun's magnetic
  field. Predictions of this kind provide opportunities to improve the
  models, forging the path to improved space weather prediction.

---------------------------------------------------------
Title: 3D MHD Modeling of Prominence Formation and Eruption
Authors: Torok, Tibor
2018cosp...42E3414T    Altcode:
  The formation of prominences in the solar corona is widely thought
  to be caused by plasma evaporation and condensation via thermal
  non-equilibrium. This process has been previously modeled by
  one-dimensional hydrodynamic simulations along individual field lines
  within static magnetic fields. A more realistic modeling of prominence
  formation can be achieved through the use of three-dimensional
  thermodynamic MHD simulations with time-dependent magnetic fields,
  which has only become feasible within the last few years. In this talk
  I will describe recent three-dimensional simulations that display the
  formation and eruption of prominence-like structures. The capabilities
  and limitations of these simulations will be discussed, along with
  the next steps that lie ahead.

---------------------------------------------------------
Title: The formation and eruption of external flux ropes in emerging
    active regions;
Authors: Leake, James Edward; Torok, Tibor
2018shin.confE..79L    Altcode:
  Solar eruptions such as CMEs and coronal jets arise from the presence of
  filament channels (FCs), which are located above the polarity inversion
  lines (PILs) of photospheric magnetic fields. Observational studies of
  FC formation is limited to a handful of cases, and so the underlying
  mechanism of FC formation has not yet been clarified

---------------------------------------------------------
Title: Generalizing the RBSL-method for Flux Ropes with Various
    Current Profiles and Nonzero External Axial Field
Authors: Titov, Viacheslav; Linker, Jon; Mikic, Zoran; Downs, Cooper;
   Torok, Tibor; Caplan, Ronald; Wijaya, Janvier
2018cosp...42E3391T    Altcode:
  Magnetic flux ropes (FRs) likely play a key role in prominence formation
  and solar eruptions.It is therefore important to develop methods for
  constructing FR configurations constrained by observational data.With
  this aim, we have recently derived a pair of regularized Biot-Savart
  laws (RBSLs; Titov et al. 2017) that allow one to efficiently calculate
  the magnetic vector potential of an FR with circular cross-sections
  and an axis of arbitrary shape.One of the RBSLs represents the axial
  component of the vector potential produced by the axial current of the
  FR, while the other represents the azimuthal component produced by the
  axial flux of the FR.The kernels of the RBSLs are regularized at the
  axis in such a way that, when the axis is straight, the RBSLs define a
  cylindrical flux rope whose structure is exactly force-free.Therefore,
  a curved thin FR defined by the RBSLs with the same kernels is
  approximately force-free.Originally, we implemented the RBSLs only
  for FRs that have a parabolic profile of the axial current and a
  vanishing axial magnetic field at the FR surface.Here we present a
  two-parametric generalization of the method that describes FRs with
  various axial-current profiles and a nonvanishing external axial field
  existing in sheared configurations.To benchmark this generalization, we
  applied it first to simple configurations of a toroidal-arc FR embedded
  into a potential background field, which are geometrically similar to
  the model proposed by Titov &amp; Démoulin (1999).We investigated the
  numerical FR equilibria reached in zero-beta MHD relaxations of these
  configurations in dependence of the initial axial-current profile
  and the strength of the external axial field. We plan to apply the
  generalized RBSLs to more realistic and complex configurations. Our
  previous successful applications of the RBSLs for FRs with a parabolic
  axial-current profile suggest the following. The shape of the FR
  axis can be determined in more complicated cases by tracking the
  observed polarity inversion line of the eruptions' source region and
  estimating its height variation as well as other FR parameters by means
  of a potential field extrapolated from the observed magnetogram. This
  research was supported by NASA's HSR, LWS, and HGI programs,NSF grants
  AGS-1560411 and AGS-1135432,and AFOSR contract FA9550-15-C-0001.

---------------------------------------------------------
Title: Data-constrained simulation of a Double-decker Eruption
Authors: Savcheva, Antonia; Kliem, B.; Downs, Copper; Torok, Tibor
2018shin.confE..91S    Altcode:
  We present the challenges we encountered in producing the initial
  condition for the hypnotized double-decker flux rope eruption on
  12/07/12. We then use this I.C. in Kliem-Torok zero-beta MHD simulation
  to produce an eruption and reproduce overall magnetic field structure
  of the eruption. We also produce a full thermodynamic simulation with
  MAS of a simpler IC which also produces similarities to the observed
  ribbons and dimmings. Both approaches have their advantages.

---------------------------------------------------------
Title: The Role of Emerging Magnetic Flux in the Initiation of
    Solar Eruptions
Authors: Linton, Mark; Torok, Tibor; Leake, James; Schuck, Pete
2018cosp...42E2029L    Altcode:
  The eruption of solar magnetic fields, generating flares and coronal
  mass ejections,and accelerating energetic particles, can have
  significant effects on the Earth'sspace environment. The source
  of these eruptions is ultimately the magnetic fieldwhich emerges
  from the solar interior into the solar atmosphere to energize the
  coronalmagnetic field. We will review theoretical and observational
  evidence for thegeneration of eruptions by flux emergence. We will
  then report on a series of numericalexperiments exploring how dynamic
  flux emergence into either potential or pre-energizedcoronal fields
  can lead to eruptions.This work was supported by the NASA Living with
  a Star program.

---------------------------------------------------------
Title: Using MHD Simulations for Space-Weather Forecasting: Where
    do we Stand?
Authors: Torok, Tibor; Linker, Jon; Mikic, Zoran; Riley, Pete; Titov,
   Viacheslav; Lionello, Roberto; Downs, Cooper; Caplan, Ronald; Wijaya,
   Janvier
2018cosp...42E3415T    Altcode:
  Coronal mass ejections (CMEs) are the main driver of space-weather
  disturbances in the terrestrial magnetosphere. Predicting the impact
  of CMEs before they arrive at Earth is one of the main challenges
  of solar and heliospheric physics. A candidate tool for this purpose
  are numerical simulations. State-of-the-art MHD simulations are now
  capable of modeling CMEs all the way from Sun to Earth, but they
  are computationally still too demanding to be used for real-time
  modeling. At present, only a simplified model (ENLIL), which does not
  include the corona and simulates CMEs as velocity perturbations, is used
  for operational space-weather forecast. However, given the continuous
  increase of computing power, more sophisticated simulations may become
  available for this purpose in the near future, and first attempts
  are currently made to prepare for operational use. A specific task at
  hand is to evaluate the accuracy of these simulations in reproducing
  in-situ measurements at Earth. I this presentation, we will briefly
  review state-of-the-art CME simulations and discuss their predictive
  capabilities and limitations. As an example, we will present a recent
  Sun-to-Earth simulation of the well-known 14 July 2000 "Bastille-Day"
  event, which produced a very strong geomagnetic storm.

---------------------------------------------------------
Title: Coordinated Observations and Modeling of Accelerated Particles
    at the Sun and in the Inner Heliosphere
Authors: Schwadron, Nathan; Mays, M. Leila; Linker, Jon; Spence,
   Harlan; Townsend, Lawrence; De Wet, Wouter; Gorby, Matthew; Wilson,
   . Jody; Odstrcil, Dusan; Downs, Cooper; Torok, Tibor; Winslow, Reka;
   Caplan, Ronald; Niehof, Jon
2018cosp...42E3043S    Altcode:
  Acute space radiation hazards pose one of the most serious risks to
  future human and robotic exploration. Large solar energetic particle
  (SEP) events are dangerous to astronauts and equipment. A fundamental
  question remains as to how large SEP events are formed, how they are
  related to coronal mass ejections (CMEs) and active region eruptions,
  and what factors control the differential fluxes incident at Earth
  and other observers during SEP events. The current evolution of the
  Sun between solar cycles 23 and 24 and during cycle 24 remains highly
  anomalous compared to previous periods of the space age. The Sun has
  been abnormally quiet over a relatively long solar minimum when galactic
  cosmic rays (GCRs) achieved the highest flux levels observed in the
  space age, and the power, pressure, flux and magnetic flux of the solar
  wind were at the lowest levels. Despite the continued paucity of solar
  activity, one of the hardest solar events in almost a decade occurred
  in September 2017 after more than a year of all-clear periods. The
  2017 September event demonstrates the importance of large fluxes of
  suprathermal seed populations and fast, large CMEs that drive shocks
  and compressions low in the corona (&lt;5 Rs) where large SEP events
  are accelerated. The Coronal-Solar Wind Energetic Particle Acceleration
  (C-SWEPA) modeling effort and the SPE Threat Assessment Tool (STAT)
  combine the Earth-Moon-Mars Radiation Environment Modules (EMMREM)
  that describe energetic particles and their effects, with the CORHEL
  (Corona-Heliosphere) modeling suite developed by the Predictive Science,
  Inc. (PSI) group. C-SWEPA has also developed coupling between EMMREM
  and Enlil at the CCMC. The C-SWEPA and STAT projects have resulted
  in coupled models that describe the conditions of the corona, solar
  wind, CMEs, associated shocks, particle acceleration, and propagation
  via physics-based modules. Recent simulations demonstrate how CMEs
  form powerful compressions and shocks low in the corona that rapidly
  accelerate high energy particles often up to the GeV energies required
  for Ground Level Enhancements (GLEs). The most pronounced acceleration
  of the CME occurs very close to the Sun (&lt;2 Rs) causing extremely
  strong compression on the flanks and nose of the CME. Results from
  recent modeling and observational studies demonstrate that the size
  of the shock or compression limits the break energy and longitudinal
  distribution of SEPs. The new capabilities afforded by STAT and C-SWEPA
  highlight the pathway toward prediction for large SEPs, and provide
  an important resource for answering fundamental new questions likely
  to arise from Parker Solar Probe and Solar Orbiter measurements.

---------------------------------------------------------
Title: Evaluating Uncertainties in Coronal Electron Temperature
    and Radial Speed Measurements Using a Simulation of the Bastille
    Day Eruption
Authors: Reginald, Nelson; St. Cyr, Orville; Davila, Joseph;
   Rastaetter, Lutz; Török, Tibor
2018SoPh..293...82R    Altcode:
  Obtaining reliable measurements of plasma parameters in the Sun's
  corona remains an important challenge for solar physics. We previously
  presented a method for producing maps of electron temperature and
  speed of the solar corona using K-corona brightness measurements made
  through four color filters in visible light, which were tested for
  their accuracies using models of a structured, yet steady corona. In
  this article we test the same technique using a coronal model of the
  Bastille Day (14 July 2000) coronal mass ejection, which also contains
  quiet areas and streamers. We use the coronal electron density,
  temperature, and flow speed contained in the model to determine two
  K-coronal brightness ratios at (410.3, 390.0 nm) and (423.3, 398.7
  nm) along more than 4000 lines of sight. Now assuming that for real
  observations, the only information we have for each line of sight are
  these two K-coronal brightness ratios, we use a spherically symmetric
  model of the corona that contains no structures to interpret these
  two ratios for electron temperature and speed. We then compare the
  interpreted (or measured) values for each line of sight with the
  true values from the model at the plane of the sky for that same line
  of sight to determine the magnitude of the errors. We show that the
  measured values closely match the true values in quiet areas. However,
  in locations of coronal structures, the measured values are predictably
  underestimated or overestimated compared to the true values, but can
  nevertheless be used to determine the positions of the structures
  with respect to the plane of the sky, in front or behind. Based on our
  results, we propose that future white-light coronagraphs be equipped
  to image the corona using four color filters in order to routinely
  create coronal maps of electron density, temperature, and flow speed.

---------------------------------------------------------
Title: Partially Open Fields and Solar Eruptions
Authors: Linker, Jon; Mikic, Zoran; Downs, Cooper; Caplan, Ronald M.;
   Riley, Pete; Torok, Tibor; Titov, Viacheslav S.; Lionello, Roberto;
   Amari, Tahar
2018tess.conf10905L    Altcode:
  Partially Open Fields and Solar Eruptions* <P />Major solar eruptions
  such as X-class flares and coronal mass ejections (CMEs) are the
  progenitors of solar energetic particles and geomagnetic storms, and are
  thus key drivers of space weather at Earth. The solar magnetic field
  is the ultimate source of these massive events, the energy of which
  is believed to be stored as free magnetic energy (energy above the
  potential field state) prior to eruption. The amount of free magnetic
  energy available in a given region is therefore a crucial indicator
  of its propensity for eruption. However, solar active regions,
  from which the largest events originate, can store widely varying
  amounts of energy. Therefore, estimates of the free energy alone are
  likely to be insufficient for knowing when a region will erupt; we
  must also estimate the bounds on how much energy can be stored in a
  given region. <P />The Aly-Sturrock theorem (Aly, ApJ 1991; Sturrock,
  ApJ 1991) shows that the energy of a fully force-free field cannot
  exceed the energy of the so-called open field. If the theorem holds,
  this places an upper limit on the amount of free energy that can
  be stored. In this paper, we describe how a closely related field,
  the partially open field (Wolfson &amp; Low ApJ 1992; Hu, ApJ 2004;
  Aly &amp; Amari, GAFD 2007), may place a much tighter bound on energy
  storage and yield insights as to when major eruptions from an active
  region are imminent (Amari et al., Nature, 2014). We demonstrate
  the idea for AR9077, the source of the July 14, 2000 "Bastille Day"
  flare/CME. <P />*Research supported by NASA and AFOSR

---------------------------------------------------------
Title: Evaluating Uncertainties in Coronal Electron Temperature and
    Radial Speed Measurements Using a Simulation of the Bastille-Day
    Eruption
Authors: Reginald, Nelson Leslie; St Cyr, O. C.; Davila, Joseph M.;
   Rastaetter, Lutz; Torok, Tibor
2018tess.conf10410R    Altcode:
  Obtaining reliable measurements of plasma parameters in the Sun's corona
  remains an important challenge for solar physics. We have previously
  conducted field experiments using MACS and ISCORE instruments to create
  maps of electron temperature and speed in the plane of the sky of
  the solar corona using K-corona brightness measurements made through
  four color filters in visible light. These instrumental techniques
  were tested for their accuracy by conducting synthetic observations
  on models that contained streamers and quiet areas and results were
  presented in (Reginald et al., 2014, Solar Phys., 289, 2021). Here,
  we present similar results from conducting synthetic observations
  on a coronal model of the Bastille-Day (July 14, 2000) coronal mass
  ejection that also contains streamers and quiet regions. We use the
  coronal electron density, temperature, and flow speed contained in
  the Bastille-Day model to determine two K-coronal brightness ratios at
  (410.0, 390.0 nm) and (423.3, 398.7 nm) along more than 4000 lines of
  sight on eight select frames. Now assuming that, for real observations,
  the only information we have for each line of sight are these two
  K-coronal brightness ratios, we then use a spherically symmetric model
  of the corona that contains no structures to interpret these two ratios
  for electron temperature and speed in the plane of the sky. Finally,
  for each line of sight, we compare the interpreted (or measured)
  value with the true value from the Bastille-Day model in the plane
  of the sky to determine the magnitude of the error. An example of the
  three step process applied on one frame in the Bastille-Day model is
  shown in the image. We show that the measured values closely match
  the true values in quiet areas. However, in locations of coronal
  structures the measured values are predictably underestimated or
  overestimated over the true values, but can nevertheless be used to
  determine the positions of the structures with respect to the plane
  of the sky, in front or behind. Our results show the potential for
  future white-light coronagraphs be equipped with four color filters
  instead of the customary single filter to produce synoptic maps of
  electron density, temperature and flow speed in the plane of the sky.

---------------------------------------------------------
Title: Sun-To-Earth MHD Simulation of the 14 JULY 2000 "Bastille
    Day" Eruption
Authors: Torok, Tibor; Downs, Cooper; Linker, Jon A.; Lionello,
   Roberto; Titov, Viacheslav S.; Mikic, Zoran; Riley, Pete; Caplan,
   Ron M.; Wijaya, Janvier
2018EGUGA..20.5564T    Altcode:
  Solar eruptions are the main driver of space-weather disturbances at
  the Earth. Extreme events are of particular interest, not only because
  of the scientific challenges they pose, but also because of their
  possible societal consequences. Here we present a magnetohydrodynamic
  (MHD) simulation of the 14 July 2000 “Bastille Day" eruption,
  which produced a very strong geomagnetic storm. After constructing a
  “thermodynamic" MHD model of the corona and solar wind, we insert a
  magnetically stable flux rope along the polarity inversion line of
  the eruption's source region and initiate the eruption by boundary
  flows. More than 10<SUP>33</SUP> ergs of magnetic energy are released
  in the eruption within a few minutes, driving a flare, an EUV wave, and
  a coronal mass ejection (CME) that travels in the outer corona at ≈
  1500 km s<SUP>-1</SUP>, close to the observed speed. We then propagate
  the CME to Earth, using a heliospheric MHD code. Our simulation thus
  provides the opportunity to test how well in situ observations of
  extreme events are matched if the eruption is initiated from a stable
  magnetic-equilibrium state. We find that the flux-rope center is very
  similar in character to the observed magnetic cloud, but arrives
  ≈ 8.5 hours later and ≈ 15° too far to the North, with field
  strengths that are too weak by a factor of ≈ 1.6. The front of the
  flux rope is highly distorted, exhibiting localized magnetic-field
  concentrations as it passes 1 AU. We discuss these properties with
  regard to the development of space-weather predictions based on MHD
  simulations of solar eruptions.

---------------------------------------------------------
Title: Sun-to-Earth MHD Simulation of the 2000 July 14 “Bastille
    Day” Eruption
Authors: Török, Tibor; Downs, Cooper; Linker, Jon A.; Lionello, R.;
   Titov, Viacheslav S.; Mikić, Zoran; Riley, Pete; Caplan, Ronald M.;
   Wijaya, Janvier
2018ApJ...856...75T    Altcode: 2018arXiv180105903T
  Solar eruptions are the main driver of space-weather disturbances at
  Earth. Extreme events are of particular interest, not only because
  of the scientific challenges they pose, but also because of their
  possible societal consequences. Here we present a magnetohydrodynamic
  (MHD) simulation of the 2000 July 14 “Bastille Day” eruption,
  which produced a very strong geomagnetic storm. After constructing
  a “thermodynamic” MHD model of the corona and solar wind, we
  insert a magnetically stable flux rope along the polarity inversion
  line of the eruption’s source region and initiate the eruption
  by boundary flows. More than 10<SUP>33</SUP> erg of magnetic energy
  is released in the eruption within a few minutes, driving a flare,
  an extreme-ultraviolet wave, and a coronal mass ejection (CME) that
  travels in the outer corona at ≈1500 km s<SUP>-1</SUP>, close to the
  observed speed. We then propagate the CME to Earth, using a heliospheric
  MHD code. Our simulation thus provides the opportunity to test how well
  in situ observations of extreme events are matched if the eruption is
  initiated from a stable magnetic equilibrium state. We find that the
  flux-rope center is very similar in character to the observed magnetic
  cloud, but arrives ≈8.5 hr later and ≈15° too far to the north,
  with field strengths that are too weak by a factor of ≈1.6. The front
  of the flux rope is highly distorted, exhibiting localized magnetic
  field concentrations as it passes 1 au. We discuss these properties
  with regard to the development of space-weather predictions based on
  MHD simulations of solar eruptions.

---------------------------------------------------------
Title: The Origin, Early Evolution and Predictability of Solar
    Eruptions
Authors: Green, Lucie M.; Török, Tibor; Vršnak, Bojan; Manchester,
   Ward; Veronig, Astrid
2018SSRv..214...46G    Altcode: 2018arXiv180104608G
  Coronal mass ejections (CMEs) were discovered in the early 1970s
  when space-borne coronagraphs revealed that eruptions of plasma
  are ejected from the Sun. Today, it is known that the Sun produces
  eruptive flares, filament eruptions, coronal mass ejections and failed
  eruptions; all thought to be due to a release of energy stored in
  the coronal magnetic field during its drastic reconfiguration. This
  review discusses the observations and physical mechanisms behind this
  eruptive activity, with a view to making an assessment of the current
  capability of forecasting these events for space weather risk and impact
  mitigation. Whilst a wealth of observations exist, and detailed models
  have been developed, there still exists a need to draw these approaches
  together. In particular more realistic models are encouraged in order
  to asses the full range of complexity of the solar atmosphere and the
  criteria for which an eruption is formed. From the observational side,
  a more detailed understanding of the role of photospheric flows and
  reconnection is needed in order to identify the evolutionary path that
  ultimately means a magnetic structure will erupt.

---------------------------------------------------------
Title: Regularized Biot-Savart Laws for Modeling Magnetic Flux Ropes
Authors: Titov, Viacheslav S.; Downs, Cooper; Mikić, Zoran; Török,
   Tibor; Linker, Jon A.; Caplan, Ronald M.
2018ApJ...852L..21T    Altcode: 2017arXiv171206708T
  Many existing models assume that magnetic flux ropes play a key role
  in solar flares and coronal mass ejections (CMEs). It is therefore
  important to develop efficient methods for constructing flux-rope
  configurations constrained by observed magnetic data and the morphology
  of the pre-eruptive source region. For this purpose, we have derived
  and implemented a compact analytical form that represents the magnetic
  field of a thin flux rope with an axis of arbitrary shape and circular
  cross-sections. This form implies that the flux rope carries axial
  current I and axial flux F, so that the respective magnetic field is the
  curl of the sum of axial and azimuthal vector potentials proportional
  to I and F, respectively. We expressed the vector potentials in terms
  of modified Biot-Savart laws, whose kernels are regularized at the
  axis in such a way that, when the axis is straight, these laws define a
  cylindrical force-free flux rope with a parabolic profile for the axial
  current density. For the cases we have studied so far, we determined
  the shape of the rope axis by following the polarity inversion line of
  the eruptions’ source region, using observed magnetograms. The height
  variation along the axis and other flux-rope parameters are estimated
  by means of potential-field extrapolations. Using this heuristic
  approach, we were able to construct pre-eruption configurations for
  the 2009 February 13 and 2011 October 1 CME events. These applications
  demonstrate the flexibility and efficiency of our new method for
  energizing pre-eruptive configurations in simulations of CMEs.

---------------------------------------------------------
Title: Predicting the Magnetic Properties of ICMEs: A Pragmatic View
Authors: Riley, P.; Linker, J.; Ben-Nun, M.; Torok, T.; Ulrich, R. K.;
   Russell, C. T.; Lai, H.; de Koning, C. A.; Pizzo, V. J.; Liu, Y.;
   Hoeksema, J. T.
2017AGUFMSH31D..08R    Altcode:
  The southward component of the interplanetary magnetic field plays
  a crucial role in being able to successfully predict space weather
  phenomena. Yet, thus far, it has proven extremely difficult to forecast
  with any degree of accuracy. In this presentation, we describe an
  empirically-based modeling framework for estimating Bz values during
  the passage of interplanetary coronal mass ejections (ICMEs). The model
  includes: (1) an empirically-based estimate of the magnetic properties
  of the flux rope in the low corona (including helicity and field
  strength); (2) an empirically-based estimate of the dynamic properties
  of the flux rope in the high corona (including direction, speed,
  and mass); and (3) a physics-based estimate of the evolution of the
  flux rope during its passage to 1 AU driven by the output from (1) and
  (2). We compare model output with observations for a selection of events
  to estimate the accuracy of this approach. Importantly, we pay specific
  attention to the uncertainties introduced by the components within
  the framework, separating intrinsic limitations from those that can
  be improved upon, either by better observations or more sophisticated
  modeling. Our analysis suggests that current observations/modeling are
  insufficient for this empirically-based framework to provide reliable
  and actionable prediction of the magnetic properties of ICMEs. We
  suggest several paths that may lead to better forecasts.

---------------------------------------------------------
Title: 3D MHD Modeling of Prominence Formation by Plasma Evaporation
    and Condensation
Authors: Torok, T.; Lionello, R.; Mikic, Z.; Downs, C.; Titov, V. S.
2017AGUFMSH41C..07T    Altcode:
  The formation of prominence material in the solar corona still belongs
  to the open questions of solar physics. There exists a consensus
  that prominence plasma has to be of chromospheric origin, but the
  mechanisms by which it accumulates in the corona are still not well
  understood. The presently most accepted scenario invokes the evaporation
  of chromospheric plasma via foot point heating and its subsequent
  condensation in the corona via thermal instabilities. This scenario
  has been successfully modeled in 1D hydrodynamic simulations along
  single field lines of a static magnetic field, but a more appropriate,
  fully 3D treatment of the thermodynamics in time-dependent magnetic
  fields was started just very recently by Xia et al. Our group at
  PSI has recently begun to engage in this challenging task as well,
  using our time-dependent, fully 3D thermodynamic MHD code MAS. For
  our investigation we consider two different coronal flux-rope
  configurations, using the analytical model by Titov and Démoulin and
  a model in which an elongated flux rope is constructed by photospheric
  flows. We investigate the plasma behavior for both configurations,
  using heating models of different complexity, and accompany our analysis
  by 1D loop simulations performed along selected field lines. In this
  presentation, we outline our modeling approach and discuss the results
  obtained so far.

---------------------------------------------------------
Title: Ion Charge States in the July 14, 2000 CME: MHD Simulations
Authors: Lionello, R.; Riley, P.; Torok, T.; Linker, J.; Mikic, Z.;
   Raymond, J. C.; Shen, C.
2017AGUFMSH11B2438L    Altcode:
  In situ measurements of ion fractional charge states at 1 AU and
  elsewhere can provide important information about electron temperatures
  back in the corona, since, once "frozen in," the charge states remain
  essentially unaltered as they travel through the solar wind. For
  example, high-ionization states suggest that the plasma originated
  from hotter regions on the solar corona. However, connecting these
  in situ measurements with remote spectroscopic observations has
  proven difficult. Using a global MHD model of the solar corona and
  heliosphere, which includes the self-consistent calculation of minor
  ion charge states, we compute the fractional charge state profiles of
  several ions associated with the CME that occurred on July 14, 2000
  and the ambient solar wind. Our approach is based on non-equilibrium
  ionization calculations, which are more accurate than the standard
  ionization equilibrium way of computing charge states. We follow the
  evolution of these profiles, together with the magnetofluid parameters
  as the plasma propagates from the low corona to 1 AU. We discuss the
  results of the CME simulations, compare them with in situ measurements,
  and relate them to theories for the origin of CMEs.

---------------------------------------------------------
Title: Thermal energy creation and transport and X-ray/EUV emission
    in a thermodynamic MHD CME simulation
Authors: Reeves, K.; Mikic, Z.; Torok, T.; Linker, J.; Murphy, N. A.
2017AGUFMSH11C..07R    Altcode:
  We model a CME using the PSI 3D numerical MHD code that includes
  coronal heating, thermal conduction and radiative cooling in the
  energy equation. The magnetic flux distribution at 1 Rs is produced by
  a localized subsurface dipole superimposed on a global dipole field,
  mimicking the presence of an active region within the global corona. We
  introduce transverse electric fields near the neutral line in the
  active region to form a flux rope, then a converging flow is imposed
  that causes the eruption. We follow the formation and evolution of
  the current sheet and find that instabilities set in soon after the
  reconnection commences. We simulate XRT and AIA EUV emission and find
  that the instabilities manifest as bright features emanating from the
  reconnection region. We examine the quantities responsible for plasma
  heating and cooling during the eruption, including thermal conduction,
  radiation, adiabatic compression and expansion, coronal heating and
  ohmic heating due to dissipation of currents. We find that the adiabatic
  compression plays an important role in heating the plasma around the
  current sheet, especially in the later stages of the eruption when the
  instabilities are present. Thermal conduction also plays an important
  role in the transport of thermal energy away from the current sheet
  region throughout the reconnection process.

---------------------------------------------------------
Title: Regularized Biot-Savart Laws for Modeling Magnetic
    Configurations with Flux Ropes
Authors: Titov, V. S.; Downs, C.; Mikic, Z.; Torok, T.; Linker, J.
2017AGUFMSH12A..06T    Altcode:
  Many existing models assume that magnetic flux ropes play a key role
  in solar flares and coronal mass ejections (CMEs). It is therefore
  important to develop efficient methods for constructing flux-rope
  configurations constrained by observed magnetic data and the initial
  morphology of CMEs. For this purpose, we have derived and implemented
  a compact analytical form that represents the magnetic field of
  a thin flux rope with an axis of arbitrary shape and a circular
  cross-section. This form implies that the flux rope carries axial
  current I and axial flux F, so that the respective magnetic field is the
  curl of the sum of toroidal and poloidal vector potentials proportional
  to I and F, respectively. We expressed the vector potentials in terms
  of modified Biot-Savart laws whose kernels are regularized at the axis
  in such a way that these laws define a cylindrical force-free flux
  rope with a parabolic profile of the axial current density, when the
  axis is straight. For the cases we have studied so far, we determined
  the shape of the rope axis by following the polarity inversion line of
  the eruptions' source region, using observed magnetograms. The height
  variation along the axis and other flux-rope parameters are estimated
  by means of potential field extrapolations. Using this heuristic
  approach, we were able to construct pre-eruption configurations for
  the 2009 February13 and 2011 October 1 CME events. These applications
  demonstrate the flexibility and efficiency of our new method for
  energizing pre-eruptive configurations in MHD simulations of CMEs. We
  discuss possible ways of optimizing the axis paths and other extensions
  of the method in order to make it more useful and robust. Research
  supported by NSF, NASA's HSR and LWS Programs, and AFOSR.

---------------------------------------------------------
Title: Modeling the 21 August 2017 Total Solar Eclipse: Prediction
    Results and New Techniques
Authors: Downs, C.; Mikic, Z.; Caplan, R. M.; Linker, J.; Lionello,
   R.; Torok, T.; Titov, V. S.; Riley, P.; MacKay, D.; Upton, L.
2017AGUFMSH13B2475D    Altcode:
  As has been our tradition for past solar eclipses, we conducted a
  high resolution magnetohydrodynamic (MHD) simulation of the corona
  to predict the appearance of the 21 August 2017 solar eclipse. In
  this presentation, we discuss our model setup and our forward
  modeled predictions for the corona's appearance, including images
  of polarized brightness and EUV/soft X-Ray emission. We show how
  the combination of forward modeled observables and knowledge of the
  underlying magnetic field from the model can be used to interpret
  the structures seen during the eclipse. We also discuss two new
  features added to this year's prediction. First, in an attempt to
  improve the morphological shape of streamers in the low corona,
  we energize the large-scale magnetic field by emerging shear and
  canceling flux within filament channels. The handedness of the shear
  is deduced from a magnetofrictional model, which is driven by the
  evolving photospheric field produced by the Advective Flux Transport
  model. Second, we apply our new wave-turbulence-driven (WTD) model for
  coronal heating. This model has substantially fewer free parameters
  than previous empirical heating models, but is inherently sensitive to
  the 3D geometry and connectivity of the magnetic field--a key property
  for modeling the thermal-magnetic structure of the corona. We examine
  the effect of these considerations on forward modeled observables,
  and present them in the context of our final 2017 eclipse prediction
  (www.predsci.com/corona/aug2017eclipse). Research supported by NASA's
  Heliophysics Supporting Research and Living With a Star Programs.

---------------------------------------------------------
Title: Particle Radiation Sources, Propagation and Interactions
in Deep Space, at Earth, the Moon, Mars, and Beyond: Examples of
    Radiation Interactions and Effects
Authors: Schwadron, Nathan A.; Cooper, John F.; Desai, Mihir; Downs,
   Cooper; Gorby, Matt; Jordan, Andrew P.; Joyce, Colin J.; Kozarev,
   Kamen; Linker, Jon A.; Mikíc, Zoran; Riley, Pete; Spence, Harlan E.;
   Török, Tibor; Townsend, Lawrence W.; Wilson, Jody K.; Zeitlin, Cary
2017SSRv..212.1069S    Altcode: 2017SSRv..tmp...63S
  Particle radiation has significant effects for astronauts, satellites
  and planetary bodies throughout the Solar System. Acute space radiation
  hazards pose risks to human and robotic exploration. This radiation also
  naturally weathers the exposed surface regolith of the Moon, the two
  moons of Mars, and other airless bodies, and contributes to chemical
  evolution of planetary atmospheres at Earth, Mars, Venus, Titan, and
  Pluto. We provide a select review of recent areas of research covering
  the origin of SEPs from coronal mass ejections low in the corona,
  propagation of events through the solar system during the anomalously
  weak solar cycle 24 and important examples of radiation interactions
  for Earth, other planets and airless bodies such as the Moon.

---------------------------------------------------------
Title: The Physical Processes of CME/ICME Evolution
Authors: Manchester, Ward; Kilpua, Emilia K. J.; Liu, Ying D.; Lugaz,
   Noé; Riley, Pete; Török, Tibor; Vršnak, Bojan
2017SSRv..212.1159M    Altcode: 2017SSRv..tmp...90M
  As observed in Thomson-scattered white light, coronal mass ejections
  (CMEs) are manifest as large-scale expulsions of plasma magnetically
  driven from the corona in the most energetic eruptions from the
  Sun. It remains a tantalizing mystery as to how these erupting magnetic
  fields evolve to form the complex structures we observe in the solar
  wind at Earth. Here, we strive to provide a fresh perspective on the
  post-eruption and interplanetary evolution of CMEs, focusing on the
  physical processes that define the many complex interactions of the
  ejected plasma with its surroundings as it departs the corona and
  propagates through the heliosphere. We summarize the ways CMEs and
  their interplanetary CMEs (ICMEs) are rotated, reconfigured, deformed,
  deflected, decelerated and disguised during their journey through the
  solar wind. This study then leads to consideration of how structures
  originating in coronal eruptions can be connected to their far removed
  interplanetary counterparts. Given that ICMEs are the drivers of most
  geomagnetic storms (and the sole driver of extreme storms), this work
  provides a guide to the processes that must be considered in making
  space weather forecasts from remote observations of the corona.

---------------------------------------------------------
Title: Electric-current Neutralization, Magnetic Shear, and Eruptive
    Activity in Solar Active Regions
Authors: Liu, Yang; Sun, Xudong; Török, Tibor; Titov, Viacheslav S.;
   Leake, James E.
2017ApJ...846L...6L    Altcode: 2017arXiv170804411L
  The physical conditions that determine whether or not solar active
  regions (ARs) produce strong flares and coronal mass ejections (CMEs)
  are not yet well understood. Here, we investigate the association
  between electric-current neutralization, magnetic shear along polarity
  inversion lines (PILs), and eruptive activity in four ARs: two emerging
  and two well-developed ones. We find that the CME-producing ARs are
  characterized by a strongly non-neutralized total current, while the
  total current in the ARs that did not produce CMEs is almost perfectly
  neutralized. The difference in the PIL shear between these two groups
  is much less pronounced, which suggests that the degree of current
  neutralization may serve as a better proxy for assessing the ability
  of ARs to produce CMEs.

---------------------------------------------------------
Title: Neutralization of Electric Current, Magnetic Shear, and
    Eruptive Activity in Solar Active Regions
Authors: Liu, Yang; Sun, Xudong; Torok, Tibor; Titov, Viacheslav;
   Leake, James E.
2017SPD....4830002L    Altcode:
  There has been an ongoing debate on whether or not the electric currents
  in solar active regions (ARs) are neutralized. Current-neutralization
  means that the direct coronal currents that connect the AR polarity
  centers are surrounded by return currents of equal total strength
  and opposite direction, i.e. the net current is zero. Using data from
  SDO/HMI, we analyze the direct and return currents in four ARs; two
  eruptive ones and two non-eruptive ones. The eruptive ARs produced
  strong flares and CMEs (successful eruptions), while the non-eruptive
  ARs include one quiet AR that produced no strong eruptions and one that
  produced a series of failed eruptions. It is found that the eruptive
  ARs have strong net currents and large shear of the magnetic field near
  their polarity inversion lines (PILs). In contrast, the currents in
  the non-eruptive ARs are well neutralized, and the PIL-shear is rather
  small. This agrees with MHD simulations that demonstrate a relationship
  between the level of current neutralization and the amount of magnetic
  shear near the PIL. We discuss the implications of these results for
  the capability of ARs to produce strong eruptions.

---------------------------------------------------------
Title: New Techniques Used in Modeling the 2017 Total Solar Eclipse:
    Energizing and Heating the Large-Scale Corona
Authors: Downs, Cooper; Mikic, Zoran; Linker, Jon A.; Caplan, Ronald
   M.; Lionello, Roberto; Torok, Tibor; Titov, Viacheslav; Riley, Pete;
   Mackay, Duncan; Upton, Lisa
2017SPD....4820802D    Altcode:
  Over the past two decades, our group has used a magnetohydrodynamic
  (MHD) model of the corona to predict the appearance of total solar
  eclipses. In this presentation we detail recent innovations and
  new techniques applied to our prediction model for the August 21,
  2017 total solar eclipse. First, we have developed a method for
  capturing the large-scale energized fields typical of the corona,
  namely the sheared/twisted fields built up through long-term processes
  of differential rotation and flux-emergence/cancellation. Using
  inferences of the location and chirality of filament channels (deduced
  from a magnetofrictional model driven by the evolving photospheric
  field produced by the Advective Flux Transport model), we tailor a
  customized boundary electric field profile that will emerge shear along
  the desired portions of polarity inversion lines (PILs) and cancel flux
  to create long twisted flux systems low in the corona. This method
  has the potential to improve the morphological shape of streamers in
  the low solar corona. Second, we apply, for the first time in our
  eclipse prediction simulations, a new wave-turbulence-dissipation
  (WTD) based model for coronal heating. This model has substantially
  fewer free parameters than previous empirical heating models, but is
  inherently sensitive to the 3D geometry and connectivity of the coronal
  field---a key property for modeling/predicting the thermal-magnetic
  structure of the solar corona. Overall, we will examine the effect
  of these considerations on white-light and EUV observables from the
  simulations, and present them in the context of our final 2017 eclipse
  prediction model.Research supported by NASA's Heliophysics Supporting
  Research and Living With a Star Programs.

---------------------------------------------------------
Title: Regularized Biot-Savart Laws for Modeling Magnetic Flux Ropes
Authors: Titov, Viacheslav; Downs, Cooper; Mikic, Zoran; Torok, Tibor;
   Linker, Jon A.
2017SPD....4840606T    Altcode:
  Many existing models assume that magnetic flux ropes play a key role
  in solar flares and coronal mass ejections (CMEs). It is therefore
  important to develop efficient methods for constructing flux-rope
  configurations constrained by observed magnetic data and the initial
  morphology of CMEs. As our new step in this direction, we have derived
  and implemented a compact analytical form that represents the magnetic
  field of a thin flux rope with an axis of arbitrary shape and a circular
  cross-section. This form implies that the flux rope carries axial
  current I and axial flux F, so that the respective magnetic field is a
  curl of the sum of toroidal and poloidal vector potentials proportional
  to I and F, respectively. The vector potentials are expressed in terms
  of Biot-Savart laws whose kernels are regularized at the rope axis. We
  regularized them in such a way that for a straight-line axis the form
  provides a cylindrical force-free flux rope with a parabolic profile of
  the axial current density. So far, we set the shape of the rope axis
  by tracking the polarity inversion lines of observed magnetograms and
  estimating its height and other parameters of the rope from a calculated
  potential field above these lines. In spite of this heuristic approach,
  we were able to successfully construct pre-eruption configurations for
  the 2009 February13 and 2011 October 1 CME events. These applications
  demonstrate that our regularized Biot-Savart laws are indeed a very
  flexible and efficient method for energizing initial configurations
  in MHD simulations of CMEs. We discuss possible ways of optimizing
  the axis paths and other extensions of the method in order to make it
  more useful and robust.Research supported by NSF, NASA's HSR and LWS
  Programs, and AFOSR.

---------------------------------------------------------
Title: Prediction of the Solar Corona for the 2017 August 21 Total
    Solar Eclipse
Authors: Mikic, Zoran; Downs, Cooper; Linker, Jon A.; Caplan, Ronald
   M.; Lionello, Roberto; Torok, Tibor; Titov, Viacheslav; Riley, Pete;
   Mackay, Duncan; Upton, Lisa
2017SPD....4820801M    Altcode:
  It has become our tradition to predict the structure of the corona
  prior to eclipses, using a magnetohydrodynamic (MHD) model based on
  measurements of photospheric magnetic fields on the Sun. We plan to
  continue this tradition for the August 21, 2017 total solar eclipse that
  will sweep across the United States. We will predict the structure of
  the corona using SDO/HMI photospheric magnetic field data, including
  images of polarization brightness, magnetic field line traces, and
  images of simulated emission in EUV and X-rays. These images can be
  compared directly with observations of the total eclipse, as well as
  observations from SDO/AIA, Hinode/XRT, and STEREO/EUVI. This year we
  will attempt to energize the magnetic field within filament channels
  for a more realistic prediction, by constructing flux ropes at the
  locations where filament channels are observed. The handedness of the
  flux ropes will be deduced from a magnetofrictional model driven by the
  evolving photospheric field produced by the Advective Flux Transport
  model.Research supported by NASA's Heliophysics Supporting Research
  and Living With a Star Programs.

---------------------------------------------------------
Title: 2010 August 1-2 Sympathetic Eruptions. II. Magnetic Topology
    of the MHD Background Field
Authors: Titov, Viacheslav S.; Mikić, Zoran; Török, Tibor; Linker,
   Jon A.; Panasenco, Olga
2017ApJ...845..141T    Altcode: 2017arXiv170707773T
  Using a potential field source-surface (PFSS) model, we recently
  analyzed the global topology of the background coronal magnetic field
  for a sequence of coronal mass ejections (CMEs) that occurred on
  2010 August 1-2. Here we repeat this analysis for the background field
  reproduced by a magnetohydrodynamic (MHD) model that incorporates plasma
  thermodynamics. As for the PFSS model, we find that all three CME source
  regions contain a coronal hole (CH) that is separated from neighboring
  CHs by topologically very similar pseudo-streamer structures. However,
  the two models yield very different results for the size, shape,
  and flux of the CHs. We find that the helmet-streamer cusp line,
  which corresponds to a source-surface null line in the PFSS model,
  is structurally unstable and does not form in the MHD model. Our
  analysis indicates that, generally, in MHD configurations, this line
  instead consists of a multiple-null separator passing along the edge
  of disconnected-flux regions. Some of these regions are transient
  and may be the origin of the so-called streamer blobs. We show that
  the core topological structure of such blobs is a three-dimensional
  “plasmoid” consisting of two conjoined flux ropes of opposite
  handedness, which connect at a spiral null point of the magnetic
  field. Our analysis reveals that such plasmoids also appear in
  pseudo-streamers on much smaller scales. These new insights into the
  coronal magnetic topology provide some intriguing implications for solar
  energetic particle events and for the properties of the slow solar wind.

---------------------------------------------------------
Title: Magnetic Source Region Characteristics Influencing the Velocity
    of Solar Eruptions in the Corona
Authors: Kliem, B.; Chintzoglou, G.; Torok, T.; Zhang, J.; Downs, C.
2016AGUFMSH13B2292K    Altcode:
  The velocity of coronal mass ejections (CMEs) is one of the primary
  parameters determining their potential geoeffectiveness. The great
  majority of very fast CMEs receive their main acceleration already in
  the corona. We study the magnetic source region structure for a complete
  sample of 15 very fast CMEs (v &gt; 1500 km/s) during 2000-2006,
  originating within 30 deg from central meridian and find a correlation
  between CME speed and the decay index profile of the coronal field
  estimated by a PFSS extrapolation. Such a correlation is not found
  for a comparison sample of slower CMEs. We also study how the decay
  index profile is related to the structure of the photospheric field
  distribution. This is complemented by a parametric simulation study
  of flux rope eruptions using the analytic Titov-Demoulin active-region
  model for simple bipolar and quadrupolar source regions, which provide
  simple relationships between the photospheric field distribution and
  the coronal decay index profile. Very fast, moderate-velocity, and even
  confined eruptions are found. Detailed, data-constrained MHD modeling
  of a very fast and a relatively slow CME, including a comparison of
  their source region characteristics, will also be presented. Support
  by NSF and NASA's LWS program is acknowledged.

---------------------------------------------------------
Title: Core Dimming Regions as Probes of Magnetic Connectivity and
    Reconfiguration.
Authors: Downs, C.; Titov, V. S.; Jiong, Q.; Torok, T.; Linker, J.;
   Mikic, Z.
2016AGUFMSH12B..05D    Altcode:
  The early onset and evolution of a Coronal Mass Ejection (CME)
  is a process that features essential coupling between the erupting
  flux-system and the ambient corona. In this presentation we will
  discuss the deep coronal dimming signatures of three contrasting
  case-study events, and relate these signatures to the pre-event magnetic
  configuration. We model each event by inserting a stable flux-rope
  into the erupting region and then relaxing the configuration with
  a full-sun zero-beta MHD model. Structural analysis of the magnetic
  field, including maps of the squashing factor (Q), field line heights,
  and the overall connectivity can be used to paint a detailed picture
  of the likely eruption process, including where and why deep dimming
  features appear. We argue that such features are likely probes of the
  reconnection process between erupting magnetic flux and surrounding
  coronal magnetic fields--a process relevant to understanding the
  dynamic magnetic connectivity of CMEs and flux-ropes in the heliosphere.

---------------------------------------------------------
Title: Radiation Environments for Future Human Exploration Throughout
    the Solar System.
Authors: Schwadron, N.; Gorby, M.; Linker, J.; Riley, P.; Torok,
   T.; Downs, C.; Spence, H. E.; Desai, M. I.; Mikic, Z.; Joyce, C. J.;
   Kozarev, K. A.; Townsend, L. W.; Wimmer-Schweingruber, R. F.
2016AGUFMSA41B2371S    Altcode:
  Acute space radiation hazards pose one of the most serious risks to
  future human and robotic exploration. The ability to predict when and
  where large events will occur is necessary in order to mitigate their
  hazards. The largest events are usually associated with complex sunspot
  groups (also known as active regions) that harbor strong, stressed
  magnetic fields. Highly energetic protons accelerated very low in the
  corona by the passage of coronal mass ejection (CME)-driven compressions
  or shocks and from flares travel near the speed of light, arriving
  at Earth minutes after the eruptive event. Whether these particles
  actually reach Earth, the Moon, Mars (or any other point) depends on
  their transport in the interplanetary magnetic field and their magnetic
  connection to the shock. Recent contemporaneous observations during
  the largest events in almost a decade show the unique longitudinal
  distributions of this ionizing radiation broadly distributed from
  sources near the Sun and yet highly isolated during the passage of CME
  shocks. Over the last decade, we have observed space weather events
  as the solar wind exhibits extremely low densities and magnetic field
  strengths, representing states that have never been observed during the
  space age. The highly abnormal solar activity during cycles 23 and 24
  has caused the longest solar minimum in over 80 years and continues
  into the unusually small solar maximum of cycle 24. As a result of
  the remarkably weak solar activity, we have also observed the highest
  fluxes of galactic cosmic rays in the space age and relatively small
  particle radiation events. We have used observations from LRO/CRaTER to
  examine the implications of these highly unusual solar conditions for
  human space exploration throughout the inner solar system. While these
  conditions are not a show-stopper for long-duration missions (e.g., to
  the Moon, an asteroid, or Mars), galactic cosmic ray radiation remains
  a significant and worsening factor that limits mission durations. If the
  heliospheric magnetic field continues to weaken over time, as is likely,
  then allowable mission durations will decrease correspondingly. Thus, we
  examine the rapidly changing radiation environment and its implications
  for human exploration destinations throughout the inner solar system.

---------------------------------------------------------
Title: The Impact of Coronal Jets on the Solar Wind and Magnetic
    Structures in the Inner Heliosphere.
Authors: Lionello, R.; Torok, T.; Titov, V. S.; Linker, J.; Mikic,
   Z.; Leake, J. E.; Linton, M.
2016AGUFMSH53A..06L    Altcode:
  Transient, collimated plasma eruptions, so-called coronal (or X-ray)
  jets, are observed low in the corona in EUV and soft X-ray bands. They
  are thought to be triggered by reconnection between closed and open
  magnetic fields, although their formation mechanisms are not yet
  fully understood. However, coronal jets are also observed to extend
  to several solar radii, suggesting that they may provide a still
  undetermined contribution to the solar wind. We simulate coronal jets
  with our "thermodynamic" full MHD model of the solar corona by driving
  the emergence of a magnetic flux rope into an open coronal magnetic
  field. We study the impact of jets to the solar wind by varying the
  field strength of the emerging flux rope, and we follow the propagation
  of ejected magnetic structures into the inner heliosphere.

---------------------------------------------------------
Title: Sun-to-Earth MHD Modeling of Powerful Solar Eruptions
Authors: Torok, T.; Downs, C.; Linker, J.; Lionello, R.; Titov, V. S.;
   Riley, P.; Mikic, Z.
2016AGUFMSH14A..05T    Altcode:
  Large solar eruptions that produce strong flares and powerful coronal
  mass ejections are the main driver of space weather disturbances close
  to the Earth. One of the main goals of numerical simulations of such
  events is therefore to reproduce their in-situ signatures at 1 AU.This
  requires a sophisticated model of the pre-eruptive configuration, the
  initiation and early evolution of the eruption, and the large-scale
  magnetic and plasma environment in which the eruption propagates. We
  have been conducting magnetohydrodynamic (MHD) simulations that comply
  with these requirements. We first produce a steady-state MHD solution
  of the background corona that incorporates photospheric magnetic field
  measurements, realistic energy transfer in the corona, and the solar
  wind. We then use the recently developed, modified flux-rope model by
  Titov et al. to insert a stable flux rope into the source region of the
  eruption, while preserving the original magnetogram. Several instances
  of the model can be combined to account for source regions with a highly
  curved and elongated polarity inversion line (PIL). The eruption is
  then initiated by imposing plasma flows that slowly converge towards
  the PIL. Finally, we propagate the eruption to Earth, by coupling the
  coronal simulation to our heliospheric MHD code. In this presentation
  we illustrate our method for the famous "Bastille Day" event of July
  14, 2000, which produced an X5.7 flare, a fast halo CME, andan intense
  geomagnetic storm. We assess the quality of the simulation by comparing
  synthetic satellite images with the observations, and we discuss how
  well it reproduces the in-situ measurements at 1 AU. We also briefly
  present our ongoing modeling effort for the more recent event of July
  12, 2012, which was observed in great detail all the way from Sun
  to Earth.

---------------------------------------------------------
Title: A Thin-Flux-Rope Approximation as a Basis for Modeling of Pre-
    and Post-Eruptive Magnetic Configurations
Authors: Titov, V. S.; Mikic, Z.; Torok, T.; Linker, J.
2016AGUFMSH13C2313T    Altcode:
  Many existing models of solar flares and coronal mass ejections (CMEs)
  assume a key role of magnetic flux ropes in these phenomena. It is
  therefore important to have efficient methods for constructing flux-rope
  configurations consistent with the observed photospheric magnetic data
  and morphology of CMEs. As our new step in this direction, we propose
  an analytical formulation that succinctly represents the magnetic
  field of a thin flux rope, which has an axis of arbitrary shape and
  a circular cross-section with the diameter slowly varying along the
  axis. This representation implies also that the flux rope carries
  axial current I and axial flux F, so that the respective magnetic
  field is a curl of the sum of toroidal and poloidal vector potentials
  proportional to I and F, respectively. Each of the two potentials
  is individually expressed in terms of a modified Biot-Savart law
  with separate kernels, both regularized at the rope axis. We argue
  that the proposed representation is flexible enough to be used in
  MHD simulations for initializing pre-eruptive configurations in the
  low corona or post-eruptive configurations (interplanetary CMEs) in
  the heliosphere. We discuss the potential advantages of our approach,
  and the subsequent steps to be performed, to develop a fully operative
  and highly competitive method compared to existing methods. Research
  supported by NSF, NASA's HSR and LWS Programs, and AFOSR.

---------------------------------------------------------
Title: Tracking Changes in Magnetic Topology in MHD Simulations
Authors: Mikic, Z.; Titov, V. S.; Lionello, R.; Torok, T.; Linker,
   J.; Downs, C.
2016AGUFMSH43B2570M    Altcode:
  The topology of the coronal magnetic field plays a key role in the
  properties of the corona and the source of the slow solar wind. The
  concept of slip-back mapping (Titov et al. 2009) has been applied
  to detect open, closed, and disconnected flux systems formed by
  reconnection of coronal magnetic fields during a given time interval. In
  particular, this technique can identify regions where closed magnetic
  field lines became open (e.g., via interchange reconnection), and
  conversely, where open field lines became closed. We will describe the
  application of this technique to the analysis of 3D MHD simulations
  (including those of coronal jets and the propagation of "blobs" in the
  solar wind). Research supported by NASA's Living With a Star Program.

---------------------------------------------------------
Title: Coupling of Coronal and Heliospheric Magnetohydrodynamic
Models: Solution Comparisons and Verification
Authors: Merkin, V. G.; Lionello, R.; Lyon, J. G.; Linker, J.; Török,
   T.; Downs, C.
2016ApJ...831...23M    Altcode:
  Two well-established magnetohydrodynamic (MHD) codes are coupled
  to model the solar corona and the inner heliosphere. The corona is
  simulated using the MHD algorithm outside a sphere (MAS) model. The
  Lyon-Fedder-Mobarry (LFM) model is used in the heliosphere. The
  interface between the models is placed in a spherical shell above the
  critical point and allows both models to work in either a rotating
  or an inertial frame. Numerical tests are presented examining the
  coupled model solutions from 20 to 50 solar radii. The heliospheric
  simulations are run with both LFM and the MAS extension into the
  heliosphere, and use the same polytropic coronal MAS solutions as the
  inner boundary condition. The coronal simulations are performed for
  idealized magnetic configurations, with an out-of-equilibrium flux rope
  inserted into an axisymmetric background, with and without including
  the solar rotation. The temporal evolution at the inner boundary of
  the LFM and MAS solutions is shown to be nearly identical, as are the
  steady-state background solutions, prior to the insertion of the flux
  rope. However, after the coronal mass ejection has propagated through
  the significant portion of the simulation domain, the heliospheric
  solutions diverge. Additional simulations with different resolution are
  then performed and show that the MAS heliospheric solutions approach
  those of LFM when run with progressively higher resolution. Following
  these detailed tests, a more realistic simulation driven by the
  thermodynamic coronal MAS is presented, which includes solar rotation
  and an azimuthally asymmetric background and extends to the Earth’s
  orbit.

---------------------------------------------------------
Title: Solar Coronal Jets: Observations, Theory, and Modeling
Authors: Raouafi, N. E.; Patsourakos, S.; Pariat, E.; Young, P. R.;
   Sterling, A. C.; Savcheva, A.; Shimojo, M.; Moreno-Insertis, F.;
   DeVore, C. R.; Archontis, V.; Török, T.; Mason, H.; Curdt, W.;
   Meyer, K.; Dalmasse, K.; Matsui, Y.
2016SSRv..201....1R    Altcode: 2016arXiv160702108R; 2016SSRv..tmp...31R
  Coronal jets represent important manifestations of ubiquitous solar
  transients, which may be the source of significant mass and energy
  input to the upper solar atmosphere and the solar wind. While
  the energy involved in a jet-like event is smaller than that of
  "nominal" solar flares and coronal mass ejections (CMEs), jets
  share many common properties with these phenomena, in particular,
  the explosive magnetically driven dynamics. Studies of jets could,
  therefore, provide critical insight for understanding the larger,
  more complex drivers of the solar activity. On the other side of the
  size-spectrum, the study of jets could also supply important clues on
  the physics of transients close or at the limit of the current spatial
  resolution such as spicules. Furthermore, jet phenomena may hint to
  basic process for heating the corona and accelerating the solar wind;
  consequently their study gives us the opportunity to attack a broad
  range of solar-heliospheric problems.

---------------------------------------------------------
Title: The Contribution of Coronal Jets to the Solar Wind
Authors: Lionello, R.; Török, T.; Titov, V. S.; Leake, J. E.;
   Mikić, Z.; Linker, J. A.; Linton, M. G.
2016ApJ...831L...2L    Altcode: 2016arXiv161003134L
  Transient collimated plasma eruptions in the solar corona, commonly
  known as coronal (or X-ray) jets, are among the most interesting
  manifestations of solar activity. It has been suggested that these
  events contribute to the mass and energy content of the corona and
  solar wind, but the extent of these contributions remains uncertain. We
  have recently modeled the formation and evolution of coronal jets
  using a three-dimensional (3D) magnetohydrodynamic (MHD) code with
  thermodynamics in a large spherical domain that includes the solar
  wind. Our model is coupled to 3D MHD flux-emergence simulations, I.e.,
  we use boundary conditions provided by such simulations to drive a
  time-dependent coronal evolution. The model includes parametric coronal
  heating, radiative losses, and thermal conduction, which enables us to
  simulate the dynamics and plasma properties of coronal jets in a more
  realistic manner than done so far. Here, we employ these simulations to
  calculate the amount of mass and energy transported by coronal jets into
  the outer corona and inner heliosphere. Based on observed jet-occurrence
  rates, we then estimate the total contribution of coronal jets to the
  mass and energy content of the solar wind to (0.4-3.0)% and (0.3-1.0)%,
  respectively. Our results are largely consistent with the few previous
  rough estimates obtained from observations, supporting the conjecture
  that coronal jets provide only a small amount of mass and energy to the
  solar wind. We emphasize, however, that more advanced observations and
  simulations (including parametric studies) are needed to substantiate
  this conjecture.

---------------------------------------------------------
Title: Unexpectedly Strong Lorentz-Force Impulse Observed During a
    Solar Eruption
Authors: Sun, X.; Fisher, G.; Torok, T.; Hoeksema, J. T.; Li, Y.;
   CGEM Team
2016usc..confE..12S    Altcode:
  For fast coronal mass ejections (CMEs), the acceleration phase takes
  place in the low corona; the momentum process is presumably dominated by
  the Lorentz force. Using ultra-high-cadence vector magnetic data from
  the Helioseismic and Magnetic Imager (HMI) and numerical simulations,
  we show that the observed fast-evolving photospheric field can be used
  to characterize the impulse of the Lorentz force during a CME. While the
  peak Lorentz force concurs with the maximum ejecta acceleration, the
  observed total force impulse surprisingly exceeds the CME momentum by
  over an order of magnitude. We conjecture that most of the Lorentz force
  impulse is "trapped" in the thin layer of the photosphere above the HMI
  line-formation height and is counter-balanced by gravity. This implies
  a consequent upward plasma motion which we coin "gentle photospheric
  upwelling". The unexpected effect dominates the momentum processes,
  but is negligible for the energy budget, suggesting a complex coupling
  between different layers of the solar atmosphere during CMEs.

---------------------------------------------------------
Title: The Thermodynamics of Coronal Jets and Their Contribution to
    the Solar Wind
Authors: Lionello, Roberto; Török, Tibor; Titov, Viacheslav; Linker,
   Jon A.; Mikic, Zoran; James E.; Linton, Mark
2016usc..confE..11L    Altcode:
  Coronal (or X-ray) jets are transient, collimated plasma eruptions
  that are observed low in the corona in EUV and soft X-ray bands. It is
  widely accepted that they are triggered by reconnection between closed
  and open magnetic fields, but their detailed formation mechanisms are
  still under debate. Since coronal jets are often seen to extend to
  several solar radii, it has been suggested that they may contribute to
  powering the solar wind, but the amount of this contribution remains
  largely uncertain. Here we present the first MHD simulations of coronal
  jets that include the solar wind and a realistic description of the
  energy transfer in the corona ("thermodynamic MHD"). The evolution in
  our model is driven by the emergence of a magnetic flux rope into an
  open magnetic field. We find different types of jets in our simulations,
  and discuss their respective formation mechanisms, morphologies, and
  emission properties. We also analyze their energy and mass contributions
  to the solar wind, and compare them with existing estimations obtained
  from observations.

---------------------------------------------------------
Title: Core Dimming Regions as Probes of Magnetic Connectivity and
    Reconfiguration.
Authors: Downs, Cooper; Titov, Viacheslav; Qiu, Jiong; Török, Tibor;
   Linker Zoran Mikić, Jon A.
2016shin.confE.135D    Altcode:
  The early onset and evolution of a Coronal Mass Ejection (CME) is a
  process that features intimate coupling between the erupting flux-system
  and the ambient corona. In this presentation we will discuss the deep
  coronal dimming signatures of three contrasting case-study events, and
  relate these signatures to the pre-event magnetic configuration. We
  model each event by inserting a stable flux-rope into the erupting
  region and then relaxing the configuration with a full-sun zero-beta
  MHD model. Structural analysis of the magnetic field, including
  maps of generalized squashing factor (Q), field line length, and
  overall connectivity can be used to paint a detailed picture of
  the likely eruption process, including where and why deep dimming
  features appear. We argue that such features are likely probes of the
  reconnection process between erupting magnetic flux and surrounding
  coronal magnetic fields.

---------------------------------------------------------
Title: Unexpectedly Large Lorentz-Force Impulse Observed During a
    Solar Eruption
Authors: Sun, Xudong; Fisher, George; Torok, Tibor; Hoeksema, Todd;
   Li, Yan; CGEM Team
2016shin.confE.158S    Altcode:
  For fast coronal mass ejections (CMEs), the acceleration phase takes
  place in the low corona; the momentum process is presumably dominated by
  the Lorentz force. Using ultra-high-cadence vector magnetic data from
  the Helioseismic and Magnetic Imager (HMI) and numerical simulations,
  we show that the observed fast-evolving photospheric field can be used
  to characterize the impulse of the Lorentz force during a CME. While the
  peak Lorentz force concurs with the maximum ejecta acceleration, the
  observed total force impulse surprisingly exceeds the CME momentum by
  over an order of magnitude. We conjecture that most of the Lorentz force
  impulse is "trapped" in the thin layer of the photosphere above the HMI
  line-formation height and is counter-balanced by gravity. This implies
  a consequent upward plasma motion which we coin "gentle photospheric
  upwelling". The unexpected effect dominates the momentum processes,
  but is negligible for the energy budget, suggesting a complex coupling
  between different layers of the solar atmosphere during CMEs.

---------------------------------------------------------
Title: Field Line Structure of Separatrix and Qausi-Separatrix
    Magnetic Surfaces in the Solar Corona
Authors: Titov, Viacheslav S.; Mikić, Zoran; Downs, Cooper; Török,
   Tibor; Lionello, Roberto; Linker, Jon A.
2016shin.confE.132T    Altcode:
  The analysis of the magnetic field topology provides a key framework for
  understanding complex phenomena in the solar atmosphere and other cosmic
  plasmas where the magnetic field plays an active role. This analysis
  is facilitated by the calculation of the so-called squashing factor Q
  on the surfaces that bound or cross the magnetic configuration under
  study. The Q-factor is a dimensionless quantity that characterizes
  the divergence of the field lines on the way between their boundary
  end points. For realistic configurations, the Q-maps reveal intricate
  networks of high-Q lines, which are, in turn, the cross-sections of
  separatrix and quasi-separatrix surfaces present in the magnetic
  configuration. <P />The sheer complexity of Q-maps can often be
  difficult to interpret. To mitigate this problem, we have developed
  a new technique that allows one to efficiently compute the field
  line structure of the (quasi-)separatrix surfaces by starting from
  their high-Q lines. The underlying algorithm iteratively determines
  sets of field-line pairs that bracket null, minimum, and bald-patch
  points. Convergence of the algorithm towards the high-Q line on either
  side automatically yields approximation of the (quasi-)separatrix
  surfaces. We demonstrate the outstanding capabilities of this
  technique by reconstructing the magnetic topology for a number of
  on-going projects at Predictive Science Inc., which include coronal
  mass ejections, streamers, streamer blobs, pseudo-streamers, and
  coronal jets. <P />Research supported by NSF/SHINE and NSF/FESD,
  and by NASAś HSR and LWS Programs.

---------------------------------------------------------
Title: Unexpectedly Strong Lorentz-Force Impulse Observed During a
    Solar Eruption
Authors: Sun, Xudong; Fisher, George H.; Torok, Tibor; Hoeksema,
   Jon Todd; Li, Yan; CGEM Team
2016SPD....47.0628S    Altcode:
  For fast coronal mass ejections (CMEs), the acceleration phase takes
  place in the low corona; the momentum process is presumably dominated by
  the Lorentz force. Using ultra-high-cadence vector magnetic data from
  the Helioseismic and Magnetic Imager (HMI) and numerical simulations,
  we show that the observed fast-evolving photospheric field can be used
  to characterize the impulse of the Lorentz force during a CME. While the
  peak Lorentz force concurs with the maximum ejecta acceleration, the
  observed total force impulse surprisingly exceeds the CME momentum by
  over an order of magnitude. We conjecture that most of the Lorentz force
  impulse is "trapped" in the thin layer of the photosphere above the HMI
  line-formation height and is counter-balanced by gravity. This implies
  a consequent upward plasma motion which we coin "gentle photospheric
  upwelling". The unexpected effect dominates the momentum processes,
  but is negligible for the energy budget, suggesting a complex coupling
  between different layers of the solar atmosphere during CMEs.

---------------------------------------------------------
Title: The Contribution of Jets to Coronal and Solar Wind Energetics:
    MHD Simulations
Authors: Lionello, Roberto; Torok, Tibor; Titov, Viacheslav; Linker,
   Jon A.; Mikic, Zoran; Leake, James E.; Linton, Mark
2016SPD....4740202L    Altcode:
  Transient collimated plasma eruptions in the corona, commonly known as
  coronal jets, are among the most interesting manifestations of solar
  activity.We use the 3D MHD model with thermodynamics developed at PSI
  to investigate the origin, dynamics, and plasma properties of coronal
  jets.Our model is coupled with 3D MHD flux emergence simulations,
  i.e, we use boundary conditions provided by such simulations to
  drive a time-dependent coronal evolution. It includes parametric
  coronal heating, radiative losses, and thermal conduction in the
  energy equations.This enables us to simulate the energy transfer in
  coronal jets in a more realistic manner than done so far and to study
  the amount of energy and mass transported by these phenomena into
  the higher corona and inner heliosphere. We discuss our results and
  compare them with previous estimations obtained from observations.

---------------------------------------------------------
Title: Modeling Jets in the Corona and Solar Wind
Authors: Torok, Tibor; Lionello, Roberto; Titov, Viacheslav S.; Leake,
   James E.; Mikic, Zoran; Linker, Jon A.; Linton, Mark G.
2016EGUGA..18.2692T    Altcode: 2015arXiv151109350T
  Coronal jets are transient, collimated eruptions that occur in
  regions of open or semi-open magnetic fields in the solar corona. Our
  understanding of these events has significantly improved in recent
  years, owing to improved observational capabilities and numerical
  simulations. Yet, several important questions concerning coronal jets
  remain largely unanswered. For example: What exactly are the physical
  mechanisms that heat and accelerate the plasma? And to what extent
  do jets contribute to the heating of the corona and in providing
  mass and energy to the fast solar wind? Here we present a "new
  generation" of coronal-jet simulations that will allow us to address
  such questions in more detail than before. In contrast to previous
  simulations, our code models the large-scale corona in a spherical
  domain, uses an advanced description of the energy transfer in the
  corona ("thermodynamic MHD"), and includes the solar wind. As a first
  application, we consider a purely radial coronal magnetic field and
  a simple coronal heating function that decreases exponentially with
  height above the surface. We produce so-called standard and blowout
  jets by continuously driving the system at the lower boundary with data
  extracted from flux-emergence simulations. We discuss the formation,
  dynamics, and evolution of the jets, as well as their contribution to
  coronal heating and the solar wind.

---------------------------------------------------------
Title: Modeling Jets in the Corona and Solar Wind
Authors: Török, T.; Lionello, R.; Titov, V. S.; Leake, J. E.;
   Mikić, Z.; Linker, J. A.; Linton, M. G.
2016ASPC..504..185T    Altcode:
  Coronal jets are transient, collimated eruptions that occur in
  regions of predominantly open magnetic field in the solar corona. Our
  understanding of these events has greatly evolved in recent years but
  several open questions, such as the contribution of coronal jets to the
  solar wind, remain. Here we present an overview of the observations and
  numerical modeling of coronal jets, followed by a brief description of
  "next-generation" simulations that include an advanced description
  of the energy transfer in the corona ("thermodynamic MHD"), large
  spherical computational domains, and the solar wind. These new models
  will allow us to address some of the open questions.

---------------------------------------------------------
Title: Fast Wave Trains Associated with Solar Eruptions: Insights
    from 3D Thermodynamic MHD Simulations
Authors: Downs, C.; Liu, W.; Torok, T.; Linker, J.; Mikic, Z.;
   Ofman, L.
2015AGUFMSH22A..06D    Altcode:
  EUV imaging observations during the SDO/AIA era have provided new
  insights into a variety of wave phenomena occurring in the low
  solar corona. One example is the observation of quasi-periodic,
  fast-propagating wave trains that are associated with solar eruptions,
  including flares and CMEs. While there has been considerable
  progress in understanding such waves from both an observational
  and theoretical perspective, it remains a challenge to pin down
  their physical origin. In this work, we detail our results from
  a case-study 3D thermodynamic MHD simulation of a coronal mass
  ejection where quasi-periodic wave trains are generated during the
  simulated eruption. We find a direct correlation between the onset of
  non-steady reconnection in the flare current sheet and the generation
  of quasi-periodic wave train signatures when patchy, collimated
  downflows interact with the flare arcade. Via forward modeling of
  SDO/AIA observables, we explore how the appearance of the wave trains
  is affected by line-of-sight integration and the multi-thermal nature
  of the coronal medium. We also examine how the wave trains themselves
  are channeled by natural waveguides formed in 3D by the non-uniform
  background magnetic field. While the physical association of the
  reconnection dynamics to the generation of quasi-periodic wave trains
  appears to be a compelling result, unanswered questions posed from
  recent observations as well as future prospects will be discussed.

---------------------------------------------------------
Title: Coupling MHD Simulations of CMEs to SEP Models
Authors: Torok, T.; Gorby, M.; Linker, J.; Schwadron, N.
2015AGUFMSH11A2376T    Altcode:
  Large Solar Energetic Particle events (SEPs) are a main space
  weather hazard and extremely dangerous to astronauts and electronic
  equipmentin space. They are typically associated with fast Coronal
  Mass Ejections (CMEs). Recent results indicate that SEPs can be
  generated already inthe early phase of CME expansion low in the
  corona, but the underlyingphysical mechanisms are not yet well
  understood. State-of-the-artmagnetohydrodynamic (MHD) simulations of
  CME initiation and evolution,combined with numerical models of particle
  acceleration and propagation,provide a powerful tool to investigate
  these mechanisms. In this talk, we present recent developments in
  the coupling of CORHEL/MAS thermodynamicMHD simulations of fast CMEs
  to the EPREM particle code, and we discuss the insights that can be
  gained from such a combined modeling approach.

---------------------------------------------------------
Title: Erratum: “Slow Rise and Partial Eruption of a
    Double-decker Filament. I Observations and Interpretation'<A
    href="/abs/2012ApJ...756...59L">(2012, ApJ, 756, 59)</A>
Authors: Liu, Rui; Kliem, Bernhard; Török, Tibor; Liu, Chang; Titov,
   Viacheslav S.; Lionello, Roberto; Linker, Jon A.; Wang, Haimin
2015ApJ...814..164L    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Thermodynamic MHD Simulations of Jets in the Solar Corona
    and Inner Heliosphere
Authors: Lionello, R.; Torok, T.; Titov, V. S.; Linker, J.; Mikic,
   Z.; Leake, J. E.; Linton, M.
2015AGUFMSH11F..02L    Altcode:
  Coronal jets are transient, collimated plasma ejections that occur
  predominantly in coronal holes and are observed in EUV, soft X-ray,
  and occasionally in white-light coronagraphs. While these intriguing
  phenomena have been studied and modeled for more than two decades, the
  details of their formation mechanism(s) are not yet fully understood,
  and their potential role for the generation of the fast solar wind
  remains largely elusive. <P />Here we present 3D MHD simulations of
  coronal jets which are performed in a large computational domain (up
  to 20 solar radii) and incorporate the effects of thermal conduction,
  radiative cooling, empirical coronal heating, and the solar wind. These
  features allow us to model the plasma properties and energy transfer of
  coronal jets in a more realistic manner than done so far, and to study
  the amount of energy and mass transported by these phenomena into the
  higher corona and inner heliosphere. <P />In order to produce a jet,
  we consider a simple, purely radial background magnetic field and
  slowly introduce a magnetic flux rope into the coronal configuration
  by coupling our model to dynamic flux emergence simulations at the
  lower boundary of the computational domain. We find two types of jets
  in our simulations: a very impulsive event reminiscent of so-called
  blowout jets and a slowly developing, more extended event that produces
  a long-lasting signature in the corona. We present synthetic satellite
  images for both types of events and discuss their respective formation
  mechanisms. Our analysis is supported by a detailed investigation of
  the magnetic topology for the blowout-type case and of the transport
  of energy and plasma into the higher corona and inner heliosphere for
  the long-lasting event.

---------------------------------------------------------
Title: Slip versus Field-Line Mapping in Describing 3D Reconnection
    of Coronal Magnetic Fields
Authors: Titov, V. S.; Mikic, Z.; Torok, T.; Downs, C.; Lionello,
   R.; Linker, J.
2015AGUFMSH43A2421T    Altcode:
  We demonstrate two techniques for describing the structure of the
  coronal magnetic field and its evolution due to reconnection in
  numerical 3D simulations of the solar corona and CMEs. These techniques
  employ two types of mapping of the boundary of the computational
  domain on itself. One of them is defined at a given time moment via
  connections of the magnetic field lines to their opposite endpoints. The
  other mapping, called slip mapping, relates field line endpoints at two
  different time moments and allows one to identify the slippage of plasma
  elements due to resistivity across field lines for a given time interval
  (Titov et al. 2009). The distortion of each of these mappings can be
  measured by using the so-called squashing factor Q (Titov 2007). The
  high-Q layers computed for the first and second mappings define,
  respectively, (quasi-)separatrix surfaces and reconnection fronts in
  evolving magnetic configurations. Analyzing these structural features,
  we are able to reveal topologically different domains and reconnected
  flux systems in the configurations, in particular, open, closed and
  disconnected magnetic flux tubes, as well as quantify the related
  magnetic flux transfer. Comparison with observations makes it possible
  also to relate these features to observed morphological elements
  such as flare loops and ribbons, and EUV dimmings. We illustrate
  these general techniques by applying them to particular data-driven
  MHD simulations. *Research supported by NASA's HSR and LWS Programs,
  and NSF/SHINE and NSF/FESD.

---------------------------------------------------------
Title: How Much Energy Can Be Stored in Solar Active Region Magnetic
    Fields?
Authors: Linker, J.; Downs, C.; Torok, T.; Titov, V. S.; Lionello,
   R.; Mikic, Z.; Riley, P.
2015AGUFMSH52A..08L    Altcode:
  Major solar eruptions such as X-class flares and very fast coronal
  mass ejections usually originate in active regions on the Sun. The
  energy that powers these events is believed to be stored as free
  magnetic energy (energy above the potential field state) prior to
  eruption. While coronal magnetic fields are not in general force-free,
  active regions have very strong magnetic fields and at low coronal
  heights the plasma beta is therefore very small, making the field (in
  equilibrium) essentially force-free. The Aly-Sturrock theorem shows that
  the energy of a fully force-free field cannot exceed the energy of the
  so-called open field. If the theorem holds, this places an upper limit
  on the amount of free energy that can be stored: the maximum free energy
  (MFE) is the difference between the open field energy and the potential
  field energy of the active region. In thermodynamic MHD simulations of
  a major eruption (the July 14, 2000 'Bastille' day event) and a modest
  event (February 13, 2009, we have found that the MFE indeed bounds the
  energy stored prior to eruption. We compute the MFE for major eruptive
  events in cycles 23 and 24 to investigate the maximum amount of energy
  that can be stored in solar active regions.Research supported by AFOSR,
  NASA, and NSF.

---------------------------------------------------------
Title: Diagnosing the Properties of the Solar Wind using Magnetic
    Topology
Authors: Mikic, Z.; Titov, V. S.; Lionello, R.; Downs, C.; Linker,
   J.; Torok, T.; Riley, P.
2015AGUFMSH31C2436M    Altcode:
  Recent work suggests that the topology of the coronal magnetic field
  plays a key role in the source and properties of the slow solar wind,
  through the collection of separatrix surfaces and quasi-separatrix
  layers (QSLs) that define the S-web (Antiochos et al. 2011; Linker et
  al. 2011; Titov et al. 2011). We have accumulated extensive experience
  with using the squashing factor Q to analyze the underlying structural
  skeleton of the coronal magnetic field, to identify magnetic null
  points, separator field lines, QSLs, and separatrix surfaces, and their
  relationship with the topology of coronal hole boundaries. This will
  be extended by implementing slip mapping (Titov et al. 2009) to detect
  open, closed, and disconnected flux systems that are formed due to
  magnetic reconnection in a coronal model driven by both the differential
  rotation and evolution of the photospheric magnetic field. This idea
  is based on using forward and backward differences in time between
  the field line mapping expected from ideal MHD motions and the actual
  mapping to diagnose magnetic reconnection. This technique can identify
  regions in the photosphere where closed magnetic field lines are about
  to open (e.g., via interchange reconnection), and conversely, where open
  field lines are about to close. We will use these concepts to develop
  tools that relate the changing magnetic topology to the properties of
  the solar wind, to plan and interpret Solar Probe Plus and Solar Orbiter
  observations. Research supported by NASA's Living With a Star Program.

---------------------------------------------------------
Title: Particle Acceleration at Low Coronal Compression Regions
    and Shocks
Authors: Schwadron, N. A.; Lee, M. A.; Gorby, M.; Lugaz, N.; Spence,
   H. E.; Desai, M.; Török, T.; Downs, C.; Linker, J.; Lionello,
   R.; Mikić, Z.; Riley, P.; Giacalone, J.; Jokipii, J. R.; Kota, J.;
   Kozarev, K.
2015ApJ...810...97S    Altcode:
  We present a study on particle acceleration in the low corona
  associated with the expansion and acceleration of coronal mass ejections
  (CMEs). Because CME expansion regions low in the corona are effective
  accelerators over a finite spatial region, we show that there is a
  rigidity regime where particles effectively diffuse away and escape
  from the acceleration sites using analytic solutions to the Parker
  transport equation. This leads to the formation of broken power-law
  distributions. Based on our analytic solutions, we find a natural
  ordering of the break energy and second power-law slope (above the
  break energy) as a function of the scattering characteristics. These
  relations provide testable predictions for the particle acceleration
  from low in the corona. Our initial analysis of solar energetic particle
  observations suggests a range of shock compression ratios and rigidity
  dependencies that give rise to the solar energetic particle (SEP)
  events studied. The wide range of characteristics inferred suggests
  competing mechanisms at work in SEP acceleration. Thus, CME expansion
  and acceleration in the low corona may naturally give rise to rapid
  particle acceleration and broken power-law distributions in large
  SEP events.

---------------------------------------------------------
Title: The Origin of Net Electric Currents in Solar Active Regions
Authors: Dalmasse, K.; Aulanier, G.; Démoulin, P.; Kliem, B.; Török,
   T.; Pariat, E.
2015ApJ...810...17D    Altcode: 2015arXiv150705060D
  There is a recurring question in solar physics regarding whether or not
  electric currents are neutralized in active regions (ARs). This question
  was recently revisited using three-dimensional (3D) magnetohydrodynamic
  (MHD) numerical simulations of magnetic flux emergence into the solar
  atmosphere. Such simulations showed that flux emergence can generate
  a substantial net current in ARs. Other sources of AR currents are
  photospheric horizontal flows. Our aim is to determine the conditions
  for the occurrence of net versus neutralized currents with this second
  mechanism. Using 3D MHD simulations, we systematically impose line-tied,
  quasi-static, photospheric twisting and shearing motions to a bipolar
  potential magnetic field. We find that such flows: (1) produce
  both direct and return currents, (2) induce very weak compression
  currents—not observed in 2.5D—in the ambient field present in the
  close vicinity of the current-carrying field, and (3) can generate
  force-free magnetic fields with a net current. We demonstrate that
  neutralized currents are in general produced only in the absence of
  magnetic shear at the photospheric polarity inversion line—a special
  condition that is rarely observed. We conclude that photospheric flows,
  as magnetic flux emergence, can build up net currents in the solar
  atmosphere, in agreement with recent observations. These results thus
  provide support for eruption models based on pre-eruption magnetic
  fields that possess a net coronal current.

---------------------------------------------------------
Title: Numerical Modeling of Single and Sympathetic Solar Eruptions
Authors: Torok, Tibor
2015IAUGA..2251036T    Altcode:
  Solar eruptions such as coronal mass ejections (CMEs) and eruptive
  flares are the largest energy release processes in the solar
  system and the main driver of space weather disturbances near
  Earth. While eruptions are solitary, occasionally they appear to
  be connected in so-called sympathetic eruptions. The numerical
  modeling of (single) eruptions has significantly improved in the
  recent years. Magnetohydrodynamic (MHD) simulations are now capable of
  modeling the whole evolution of observed CMEs, from their onset in the
  low corona up to their arrival at Earth, with an unprecedented degree
  of realism. The modeling of sympathetic eruptions has very recently
  began as well, but those simulations are still very idealized. In
  this talk, I will summarize the current state of CME simulations and
  discuss briefly the next steps ahead.

---------------------------------------------------------
Title: How Much Energy Can Be Stored in Active Region Magnetic Fields?
Authors: Linker, Jon A.; Torok, Tibor; Downs, Cooper; Titov,
   Viacheslav; Lionello, Roberto; Riley, Pete; Mikic, Zoran
2015shin.confE..77L    Altcode:
  Major solar eruptions such as X-class flares and very fast coronal
  mass ejections usually originate in active regions on the Sun. The
  energy that powers these events is believed to be stored as free
  magnetic energy (energy above the potential field state) prior to
  eruption. While coronal magnetic fields are not in general force-free,
  active regions have very strong magnetic fields and at low coronal
  heights the plasma beta is very small, making the field (in equilibrium)
  essentially force-free. The Aly-Sturrock theorem shows that the energy
  of a force-free field cannot exceed the energy of the so-called open
  field. If the theorem holds, this places an upper limit on the amount
  of free energy that can be stored. We investigate the magnetic energy
  storage and release in full thermodynamic MHD simulations of a major
  event (the July 14, 2000 'Bastille' day event) and a modest event
  (February 13, 2009) and relate it to the potential and open field
  energies for these active regions. We discuss the usefulness of the
  open field energy as a guide to how much energy can be stored in an
  active region.

---------------------------------------------------------
Title: Thermodynamic 3D MHD Modeling of Coronal Jets
Authors: Lionello, Roberto; Torok, Tibor; Titov, Viacheslav S.; Leake,
   James E.; Linton, Mark G.; Linker, Jon A.; Mikic, Zoran
2015shin.confE..32L    Altcode:
  Transient collimated plasma eruptions in the corona, so-called
  'standard' and 'blowout' coronal jets, are among the most intriguing
  manifestations of solar activity. We use the PSI 'thermodynamic'
  3D MHD model to improve our understanding of the origin, dynamics,
  and plasma properties of coronal jets. Our code models the corona by
  taking into account thermal conduction, radiative cooling, empirical
  coronal heating, and the solar wind. <P />These properties enable us to
  simulate the energy transfer in coronal jets in a more realistic manner
  than done so far, and to study the amount of energy and mass transported
  by these phenomena into the higher corona and solar wind. Here we couple
  our model with 3D MHD flux emergence simulations, i.e, we use boundary
  conditions provided by such simulations to drive a time-dependent
  coronal evolution. In particular, we study the topological properties
  of the magnetic fields associated with jets, how the jet appears in
  EUV and soft X-ray emission, and its signature in the inner heliosphere.

---------------------------------------------------------
Title: Connecting the evolution and properties of CMEs to their low
    coronal signatures. A modeling case study of the ‘simple’ Feb
    13 2009 event
Authors: Downs, Cooper; Török, Tibor; Titov, Viacheslav; Liu, Wei;
   Linker, Jon; Mikić, Zoran
2015TESS....130401D    Altcode:
  The early onset and and evolution of a CME is a process that features
  an intimate coupling between the erupting flux-system and the
  ambient corona. For this reason low coronal signatures that we often
  observe in the EUV can be used to infer information on the physical
  nature and evolution of CMEs. In this presentation we will discuss
  a 3D thermodynamic MHD simulation of the Feb 13 2009 eruption,
  which occurred from an isolated region during solar minimum and
  produced well characterized EUV wave and transient coronal dimming
  features. Using observations as a guide, we simulate the entire
  evolution of the eruption and global corona, starting from the initial
  stable configuration through onset and evolution to the post-eruptive
  reconfiguration. With a particular focus on coronal dimmings, we
  track how the connectivity of the erupting flux-rope evolves with
  time and how this relates to corresponding dimmings in synthetic EUV
  observables. We find that the appearance of the core dimming regions
  and their migration over time can be related to when and where the
  erupting rope reconnects with itself and the adjacent arcade. Other
  aspects related to CME evolution, such as the generation of an EUV
  wave and quasi-periodic fast-propagating waves are also discussed.

---------------------------------------------------------
Title: Electric current neutralization in solar active regions
Authors: Dalmasse, Kévin; Aulanier, Guillaume; Török, Tibor;
   Démoulin, Pascal; Pariat, Etienne; Kliem, Bernhard
2015TESS....111303D    Altcode:
  There is a recurring question in solar physics of whether or not
  photospheric vertical electric currents are neutralized in solar active
  regions, i.e., whether or not the total electric current integrated
  over a single magnetic polarity of an active region vanishes. While
  different arguments have been proposed in favor of, or against, the
  neutralization of electric currents, both theory and observations are
  still not fully conclusive. Providing the answer to this question is
  crucial for theoretical models of solar eruptions. Indeed, if currents
  are neutralized in active regions, then any eruption model based on net
  - i.e., non-zero - electric currents, such as the torus instability,
  requires further consideration. We address the question of electric
  current neutralization in active regions using 3D zero-beta MHD
  simulations of line-tied, slow photospheric driving motions imposed
  on an initially potential magnetic field. We compare our results to a
  recent study of the build-up of coronal electric currents in an MHD
  simulation of the emergence of a current-neutralized twisted flux
  tube into the solar atmosphere. Our parametric study shows that, in
  accordance with the flux emergence simulation, photospheric motions are
  associated with the formation of both direct and return currents. It
  further shows that both processes (flux emergence and photospheric
  flows) can lead to the formation of strong net currents in the solar
  corona, and that the non-neutralization of electric currents is related
  to the presence of magnetic shear at the polarity inversion line. We
  discuss the implications of our results for the observations and for
  theoretical models of solar eruptions.

---------------------------------------------------------
Title: Magnetic Topology of the Global MHD Configuration on 2010
    August 1-2
Authors: Titov, V. S.; Mikic, Z.; Torok, T.; Linker, J.; Panasenco, O.
2014AGUFMSH23A4148T    Altcode:
  It appears that the global magnetic topology of the solar corona
  predetermines to a large extent the magnetic flux transfer during
  solar eruptions. We have recently analyzed the global topology for
  a source-surface model of the background magnetic field at the time
  of the 2010 August 1-2 sympathetic CMEs (Titov et al. 2012). Now we
  extend this analysis to a more accurate thermodynamic MHD model of
  the solar corona. As for the source-surface model, we find a similar
  triplet of pseudo-streamers in the source regions of the eruptions. The
  new study confirms that all these pseudo-streamers contain separatrix
  curtains that fan out from a basic magnetic null point, individual
  for each of the pseudo-streamers. In combination with the associated
  separatrix domes, these separatrix curtains fully isolate adjacent
  coronal holes of the like polarity from each other. However, the size
  and shape of the coronal holes, as well as their open magnetic fluxes
  and the fluxes in the lobes of the separatrix domes, are very different
  for the two models. The definition of the open separator field lines,
  where the (interchange) reconnection between open and closed magnetic
  flux takes place, is also modified, since the structurally unstable
  source-surface null lines do not exist anymore in the MHD model. In
  spite of all these differences, we reassert our earlier hypothesis
  that magnetic reconnection at these nulls and the associated separators
  likely plays a key role in coupling the successive eruptions observed
  by SDO and STEREO. The results obtained provide further validation of
  our recent simplified MHD model of sympathetic eruptions (Török et
  al. 2011). Research supported by NASA's Heliophysics Theory and LWS
  Programs, and NSF/SHINE and NSF/FESD.

---------------------------------------------------------
Title: Propagation and Evolution of Interplanetary Magnetic Clouds:
    Global Simulations and Comparisons with Observations
Authors: Riley, P.; Ben-Nun, M.; Linker, J.; Torok, T.; Lionello,
   R.; Downs, C.
2014AGUFMSH42A..05R    Altcode:
  In this talk, we explore the evolution of interplanetary coronal mass
  ejections (ICMEs), and fast magnetic clouds (MCs) in particular. We
  address three specific issues. First, What are the large-scale forces
  acting on ejecta as they travel from the Sun to 1 AU through a realistic
  ambient solar wind, and how does they affect the large-scale structure
  of the event? Second, what are the dominant waves/shocks associated with
  fast ICMEs? And third, how are the properties of ICMEs different during
  cycle 24 than during the previous cycle? To accomplish these objectives,
  we employ a variety of numerical approaches, including global resistive
  MHD models that incorporate realistic energy transport processes. We
  also compare and contrast model results with both remote solar and
  in-situ measurements of ICMEs at 1 AU and elsewhere, including the
  so-called “Bastille Day” event of July 14, 2000, and the more recent
  “extreme ICME” observed by STEREO-A on July 23, 2012.

---------------------------------------------------------
Title: Towards a Thermodynamic 3D MHD Model of Coronal Jets
Authors: Lionello, R.; Torok, T.; Linker, J.; Mikic, Z.
2014AGUFMSH53D..06L    Altcode:
  Transient collimated plasma eruptions in the corona, so-called
  "standard" and "blowout" coronal jets, are among the most intriguing
  manifestations of solar activity. We have begun to use the PSI
  "thermodynamic" 3D MHD model to improve our understanding of the
  origin, dynamics, and plasma properties of coronal jets. Our code
  models the corona by taking into account thermal conduction, radiative
  cooling, empirical coronal heating, and the solar wind, and it is
  capable of using observed magnetograms as boundary condition for the
  magnetic field. Furthermore, the model is coupled with 3D MHD flux
  emergence simulations, i.e it can use boundary conditions provided by
  such simulations to drive a time-dependent coronal evolution. These
  properties enable us to simulate the energy transfer in coronal jetsin
  a more realistic manner. We will present preliminary results.

---------------------------------------------------------
Title: Sympathetic solar eruptions in quadrupolar magnetic
    configurations
Authors: Torok, T.; Titov, V. S.; Panasenco, O.
2014AGUFMSH23A4146T    Altcode:
  Observations by SDO/AIA have renewed the interest in sympathetic
  solareruptions, i.e., of eruptions that occur simultaneously (or in
  shortsuccession) at different source regions in the corona. Recently,
  Toroket al. (2011) developed an idealized numerical model for
  the triggermechanisms of sympathetic eruptions in so-called
  pseudo-streamers, whichconsist of a tri-polar magnetic configuration
  with a parasitic polarityin their center. Here we extend the work
  by Torok et al. by investigating sympathetic eruptions in (the
  topologically somewhat more complex) quadrupolar configurations,
  using MHD simulations. We consider both symmetric and asymmetric
  initial configurations that contain two or three flux ropes within the
  quadrupole. We find, differentto Torok et al. (2011), that magnetic
  reconnection induced by a firsteruption cannot just trigger, but also
  prevent subsequent eruptions. In addition, a (relatively modest)
  asymmetry of the configuration may fully suppress the occurrence
  of successive full eruptions, i.e., of coronal mass ejections. We
  discuss the implications of these results for our understanding of
  sympathetic eruptions.

---------------------------------------------------------
Title: Particle Acceleration in the Low Corona Over Broad Longitudes:
    Coupling MHD and 3D Particle Simulations
Authors: Gorby, M.; Schwadron, N.; Torok, T.; Downs, C.; Lionello,
   R.; Linker, J.; Titov, V. S.; Mikic, Z.; Riley, P.; Desai, M. I.;
   Dayeh, M. A.
2014AGUFMSH21B4127G    Altcode:
  Recent work on the coupling between the Energetic Particle Radiation
  Environment Module (EPREM, a 3D energetic particle model) and
  Magnetohydrodynamics Around a Sphere (MAS, an MHD code developed
  at Predictive Science, Inc.) has demonstrated the efficacy of
  compression regions around fast coronal mass ejections (CMEs) for
  particle acceleration low in the corona (∼ 3 - 6 solar radii). These
  couplings show rapid particle acceleration over a broad longitudinal
  extent (∼ 80 degrees) resulting from the pile-up of magnetic flux in
  the compression regions and their subsequent expansion. The challenge
  for forming large SEP events in such compression-acceleration scenarios
  is to have enhanced scattering within the acceleration region while
  also allowing for efficient escape of accelerated particles downstream
  (away from the Sun) from the compression region. We present here
  the most recent simulation results including energetic particle and
  CME plasma profiles, the subsequent flux and dosages at 1AU, and an
  analysis of the compressional regions as efficient accelerators.

---------------------------------------------------------
Title: Slow Rise and Partial Eruption of a Double-decker
    Filament. II. A Double Flux Rope Model
Authors: Kliem, Bernhard; Török, Tibor; Titov, Viacheslav S.;
   Lionello, Roberto; Linker, Jon A.; Liu, Rui; Liu, Chang; Wang, Haimin
2014ApJ...792..107K    Altcode: 2014arXiv1407.2272K
  Force-free equilibria containing two vertically arranged magnetic flux
  ropes of like chirality and current direction are considered as a model
  for split filaments/prominences and filament-sigmoid systems. Such
  equilibria are constructed analytically through an extension of the
  methods developed in Titov &amp; Démoulin and numerically through an
  evolutionary sequence including shear flows, flux emergence, and flux
  cancellation in the photospheric boundary. It is demonstrated that
  the analytical equilibria are stable if an external toroidal (shear)
  field component exceeding a threshold value is included. If this
  component decreases sufficiently, then both flux ropes turn unstable
  for conditions typical of solar active regions, with the lower rope
  typically becoming unstable first. Either both flux ropes erupt upward,
  or only the upper rope erupts while the lower rope reconnects with
  the ambient flux low in the corona and is destroyed. However, for
  shear field strengths staying somewhat above the threshold value,
  the configuration also admits evolutions which lead to partial
  eruptions with only the upper flux rope becoming unstable and the
  lower one remaining in place. This can be triggered by a transfer of
  flux and current from the lower to the upper rope, as suggested by
  the observations of a split filament in Paper I. It can also result
  from tether-cutting reconnection with the ambient flux at the X-type
  structure between the flux ropes, which similarly influences their
  stability properties in opposite ways. This is demonstrated for the
  numerically constructed equilibrium.

---------------------------------------------------------
Title: A Method for Embedding Circular Force-free Flux Ropes in
    Potential Magnetic Fields
Authors: Titov, V. S.; Török, T.; Mikic, Z.; Linker, J. A.
2014ApJ...790..163T    Altcode:
  We propose a method for constructing approximate force-free equilibria
  in pre-eruptive configurations in which a thin force-free flux rope is
  embedded into a locally bipolar-type potential magnetic field. The flux
  rope is assumed to have a circular-arc axis, a circular cross-section,
  and electric current that is either concentrated in a thin layer at the
  boundary of the rope or smoothly distributed across it with a maximum
  of the current density at the center. The entire solution is described
  in terms of the magnetic vector potential in order to facilitate
  the implementation of the method in numerical magnetohydrodynamic
  (MHD) codes that evolve the vector potential rather than the magnetic
  field itself. The parameters of the flux rope can be chosen so that
  its subsequent MHD relaxation under photospheric line-tied boundary
  conditions leads to nearly exact numerical equilibria. To show the
  capabilities of our method, we apply it to several cases with different
  ambient magnetic fields and internal flux-rope structures. These
  examples demonstrate that the proposed method is a useful tool for
  initializing data-driven simulations of solar eruptions.

---------------------------------------------------------
Title: Catastrophe versus Instability for the Eruption of a Toroidal
    Solar Magnetic Flux Rope
Authors: Kliem, B.; Lin, J.; Forbes, T. G.; Priest, E. R.; Török, T.
2014ApJ...789...46K    Altcode: 2014arXiv1404.5922K
  The onset of a solar eruption is formulated here as either a magnetic
  catastrophe or as an instability. Both start with the same equation of
  force balance governing the underlying equilibria. Using a toroidal
  flux rope in an external bipolar or quadrupolar field as a model
  for the current-carrying flux, we demonstrate the occurrence of a
  fold catastrophe by loss of equilibrium for several representative
  evolutionary sequences in the stable domain of parameter space. We
  verify that this catastrophe and the torus instability occur at the same
  point; they are thus equivalent descriptions for the onset condition
  of solar eruptions.

---------------------------------------------------------
Title: Developing 3D CME Models
Authors: Mikic, Zoran; Torok, Tibor; Titov, Viacheslav; Linker,
   Jon A.; Reeves, Kathy
2014AAS...22421808M    Altcode:
  We describe the development of CME models in three dimensions,
  including the energization of active regions and the initiation
  of eruptions via flux cancellation. We contrast the dynamics from
  idealized zero-beta models with more sophisticated models based on
  thermodynamic solutions. We explore the effect of the strength of the
  magnetic field in the active region (or, more appropriately, the amount
  of smoothing applied to the observed magnetic field), the profiles
  for transverse field emergence or applied shear, and the nature of
  the flux cancellation, on the dynamics of eruptions. In particular,
  our interest is in understanding which effects lead to fast CMEs.

---------------------------------------------------------
Title: The evolution of writhe in kink-unstable flux ropes and
    erupting filaments
Authors: Török, T.; Kliem, B.; Berger, M. A.; Linton, M. G.;
   Démoulin, P.; van Driel-Gesztelyi, L.
2014PPCF...56f4012T    Altcode: 2014arXiv1403.1565T
  The helical kink instability of a twisted magnetic flux tube has been
  suggested as a trigger mechanism for solar filament eruptions and
  coronal mass ejections (CMEs). In order to investigate if estimations
  of the pre-emptive twist can be obtained from observations of writhe
  in such events, we quantitatively analyze the conversion of twist into
  writhe in the course of the instability, using numerical simulations. We
  consider the line tied, cylindrically symmetric Gold-Hoyle flux rope
  model and measure the writhe using the formulae by Berger and Prior
  which express the quantity as a single integral in space. We find that
  the amount of twist converted into writhe does not simply scale with
  the initial flux rope twist, but depends mainly on the growth rates
  of the instability eigenmodes of higher longitudinal order than the
  basic mode. The saturation levels of the writhe, as well as the shapes
  of the kinked flux ropes, are very similar for considerable ranges of
  initial flux rope twists, which essentially precludes estimations of
  pre-eruptive twist from measurements of writhe. However, our simulations
  suggest an upper twist limit of ∼6π for the majority of filaments
  prior to their eruption.

---------------------------------------------------------
Title: Distribution of electric currents in source regions of solar
    eruptions
Authors: Torok, Tibor; Leake, James E.; Titov, Viacheslav; Archontis,
   Vasilis; Mikic, Zoran; Linton, Mark; Dalmasse, Kevin; Aulanier,
   Guillaume; Kliem, Bernhard
2014AAS...22431202T    Altcode:
  There has been a long-lasting debate on the question of whether or
  not electric currents in the source regions of solar eruptions are
  neutralized. That is, whether or not the direct coronal currents
  connecting the photospheric polarities in such regions are surrounded
  by return currents of equal amount and opposite direction. In order to
  address this question, we consider several mechanisms of source region
  formation (flux emergence, photospheric shearing/twisting flows,
  and flux cancellation) and quantify the evolution of the electric
  currents, using 3D MHD simulations. For the experiments conducted so
  far, we find a clear dominance of the direct currents over the return
  currents in all cases in which the models produce significant magnetic
  shear along the source region's polarity inversion line. This suggests
  that pre-eruptive magnetic configurations in strongly sheared active
  regions and filament channels carry substantial net currents. We discuss
  the implications of this result for the modeling of solar eruptions.

---------------------------------------------------------
Title: Coronal Magnetic Reconnection Driven by CME Expansion—the
    2011 June 7 Event
Authors: van Driel-Gesztelyi, L.; Baker, D.; Török, T.; Pariat, E.;
   Green, L. M.; Williams, D. R.; Carlyle, J.; Valori, G.; Démoulin,
   P.; Kliem, B.; Long, D. M.; Matthews, S. A.; Malherbe, J. -M.
2014ApJ...788...85V    Altcode: 2014arXiv1406.3153V
  Coronal mass ejections (CMEs) erupt and expand in a magnetically
  structured solar corona. Various indirect observational pieces of
  evidence have shown that the magnetic field of CMEs reconnects with
  surrounding magnetic fields, forming, e.g., dimming regions distant
  from the CME source regions. Analyzing Solar Dynamics Observatory
  (SDO) observations of the eruption from AR 11226 on 2011 June 7, we
  present the first direct evidence of coronal magnetic reconnection
  between the fields of two adjacent active regions during a CME. The
  observations are presented jointly with a data-constrained numerical
  simulation, demonstrating the formation/intensification of current
  sheets along a hyperbolic flux tube at the interface between the CME
  and the neighboring AR 11227. Reconnection resulted in the formation of
  new magnetic connections between the erupting magnetic structure from
  AR 11226 and the neighboring active region AR 11227 about 200 Mm from
  the eruption site. The onset of reconnection first becomes apparent
  in the SDO/AIA images when filament plasma, originally contained
  within the erupting flux rope, is redirected toward remote areas in
  AR 11227, tracing the change of large-scale magnetic connectivity. The
  location of the coronal reconnection region becomes bright and directly
  observable at SDO/AIA wavelengths, owing to the presence of down-flowing
  cool, dense (10<SUP>10</SUP> cm<SUP>-3</SUP>) filament plasma in its
  vicinity. The high-density plasma around the reconnection region is
  heated to coronal temperatures, presumably by slow-mode shocks and
  Coulomb collisions. These results provide the first direct observational
  evidence that CMEs reconnect with surrounding magnetic structures,
  leading to a large-scale reconfiguration of the coronal magnetic field.

---------------------------------------------------------
Title: Thermal energy creation and transport and X-ray/EUV emission
    in a thermodynamic MHD CME simulation
Authors: Reeves, Kathy; Mikić, Zoran; Linker, Jon; Török, Tibor
2014shin.confE...2R    Altcode:
  We model a CME using a 3D numerical MHD code that includes coronal
  heating, thermal conduction and radiative cooling in the energy
  equation. We first develop a global coronal solution (from 1 to 20 Rs)
  to serve as the initial condition for the CME simulation. The magnetic
  flux distribution at 1 Rs is produced by a localized subsurface dipole
  superimposed on a global dipole field, to mimic the presence of an
  active region within the global corona. The resulting configuration
  has solar wind emanating from the open field regions, dense plasma in
  the streamer belt, and hot plasma in the active region. We introduce
  transverse electric fields near the neutral line in the active region
  to form a flux rope, then a converging flow is imposed that causes the
  eruption. We follow the quantities responsible for plasma heating
  and cooling during the eruption, including thermal conduction,
  radiation, adiabatic compression and expansion, coronal heating
  and ohmic heating due to dissipation of currents. We find that the
  adiabatic compression plays an important role in heating plasma around
  the current sheet and in the collapsing reconnected loops under the
  erupting flux rope. Thermal conduction also plays an important role in
  the transport of thermal energy. We follow the formation and evolution
  of the current sheet and simulate emissions in the X-ray and extreme
  ultra-violet wavelengths in order to determine signatures of current
  sheet energetics in observations from the XRT on the Hinode satellite
  and the AIA instrument on the Solar Dynamics Observatory.

---------------------------------------------------------
Title: A Method for Embedding Circular Force-Free Flux Ropes in
    Potential Magnetic Fields
Authors: Titov, Viacheslav; Torok, Tibor; Mikic, Zoran; Linker, Jon A.
2014AAS...22421204T    Altcode:
  We propose a method for constructing approximate force-free equilibria
  in pre-eruptive configurations that locally are a bipolar-type
  potential magnetic field with a thin force-free flux rope embedded
  inside it. The flux rope is assumed to have a circular-arc axis,
  circular cross-section, and electric current that is either concentrated
  in a thin layer at the boundary of the rope or smoothly distributed
  across it with a maximum of the current density at the center.The
  entire solution is described in terms of the magnetic vector
  potential in order to facilitate the implementation of the method
  in numerical magnetohydrodynamic (MHD) codes that evolve the vector
  potential rather than the magnetic field itself. The parameters of
  the flux rope can be chosen so that its subsequent MHD relaxation
  under photospheric line-tied boundary conditions leads to nearly
  exact numerical equilibria. To show the capabilities of our method,
  we apply it to several cases with different ambient magnetic fields
  and internal flux-rope structures. These examples demonstrate that
  the proposed method is a useful tool for initializing data-driven
  simulations of solar eruptions.

---------------------------------------------------------
Title: Distribution of Electric Currents in Solar Active Regions
Authors: Török, T.; Leake, J. E.; Titov, V. S.; Archontis, V.;
   Mikić, Z.; Linton, M. G.; Dalmasse, K.; Aulanier, G.; Kliem, B.
2014ApJ...782L..10T    Altcode: 2014arXiv1401.2931T
  There has been a long-standing debate on the question of whether or
  not electric currents in solar active regions are neutralized. That
  is, whether or not the main (or direct) coronal currents connecting
  the active region polarities are surrounded by shielding (or return)
  currents of equal total value and opposite direction. Both theory and
  observations are not yet fully conclusive regarding this question, and
  numerical simulations have, surprisingly, barely been used to address
  it. Here we quantify the evolution of electric currents during the
  formation of a bipolar active region by considering a three-dimensional
  magnetohydrodynamic simulation of the emergence of a sub-photospheric,
  current-neutralized magnetic flux rope into the solar atmosphere. We
  find that a strong deviation from current neutralization develops
  simultaneously with the onset of significant flux emergence into the
  corona, accompanied by the development of substantial magnetic shear
  along the active region's polarity inversion line. After the region
  has formed and flux emergence has ceased, the strong magnetic fields
  in the region's center are connected solely by direct currents, and
  the total direct current is several times larger than the total return
  current. These results suggest that active regions, the main sources
  of coronal mass ejections and flares, are born with substantial net
  currents, in agreement with recent observations. Furthermore, they
  support eruption models that employ pre-eruption magnetic fields
  containing such currents.

---------------------------------------------------------
Title: Global Magnetic Topology and Large-Scale Dynamics of the
    Solar Corona
Authors: Titov, Viacheslav; Linker, Jon; Mikic, Zoran; Riley, Pete;
   Lionello, Roberto; Downs, Cooper; Torok, Tibor
2014cosp...40E3350T    Altcode:
  We consider the global topology of the coronal magnetic field
  in relation to the large-scale dynamics of the solar corona. Our
  consideration includes recent results on the structural analysis
  of this field determined in two different approximations, namely,
  potential field source surface model and solar magnetohydrodynamic
  model. We identify similarities and differences between structural
  features of the magnetic field obtained in these two models and discuss
  their implications for understanding various large-scale phenomena in
  the solar corona. The underlying magnetic topology manifests itself
  in a variety of observed morphological features such as streamers,
  pseudo-streamers or unipolar streamers, EUV dimmings, flare ribbons,
  coronal holes, and jets. For each of them, the related magnetic
  configuration has specific structural features, whose presence has to be
  not only identified but also verified on its independence from the used
  field model in order to reliably predict the impact of such features on
  physical processes in the corona. Among them are magnetic null points
  and minima, bald patches, separatrix surfaces and quasi-separatrix
  layers, and open and closed separator field lines. These features form
  a structural skeleton of the coronal magnetic field and are directly
  involved through the ubiquitous process of magnetic reconnection in many
  solar dynamic phenomena such as coronal mass ejections, solar wind,
  acceleration and transport of energetic particles. We will pinpoint
  and elucidate in our overview some of such involvements that have
  recently received a considerable attention in our ongoing projects at
  Predictive Science.

---------------------------------------------------------
Title: Electric currents in solar active regions
Authors: Dalmasse, Kévin; Pariat, Etienne; Kliem, Bernhard; Aulanier,
   Guillaume; Demoulin, Pascal; Torok, Tibor
2014cosp...40E.613D    Altcode:
  There is a recurring question in solar physics about whether or not
  photospheric vertical electric currents are neutralized in solar active
  regions, i.e. if the total electric current integrated over a single
  photospheric magnetic polarity of an active region vanishes. Different
  arguments have been proposed in favor of, or against, the neutralization
  of electric currents, but both theory and observations are still not
  fully conclusive. The answer to this question has implications for
  eruption models. Indeed, if currents are neutralized in active regions,
  then any eruption model based on non-neutralized electric currents,
  such as the torus instability, would need to be further analyzed. We
  addressed the question of electric currents neutralization in active
  regions using 3D zero-beta, line-tied, slow driving motions of an
  initially potential magnetic field. We compared our results to a recent
  study of electric currents build-up in a MHD numerical simulation of the
  emergence of a current-neutralized twisted flux tube. Our parametric
  analyses show that, as for the emergence, photospheric motions are
  associated with the formation of both direct and return currents. It
  further shows that both processes can lead to the formation of strong
  net currents in the solar corona, and that the non-neutralization of
  electric currents is related to the presence of magnetic shear at the
  polarity inversion line. We will discuss the implications of our results
  for the observations and for the different solar eruption models.

---------------------------------------------------------
Title: Time-Dependent Coupled Coronal-Solar Wind-SEP Modeling
Authors: Linker, Jon; Mikic, Zoran; Schwadron, Nathan; Riley, Pete;
   Gorby, Matthew; Lionello, Roberto; Downs, Cooper; Torok, Tibor
2014cosp...40E1840L    Altcode:
  Solar energetic particle (SEP) events are important space weather
  phenomena. SEPs can damage satellite instrumentation, and they can be
  hazardous for crews of Low Earth Orbit spacecraft and the International
  Space Station, especially when engaged in extravehicular activity. The
  acceleration and transport of SEPs is intimately tied to the evolution
  and propagation of coronal mass ejections (CMEs) and their associated
  shock waves. In this presentation, we describe an approach to modeling
  CMEs in the corona and inner heliosphere, together with modeling of
  SEP acceleration and transport. CMEs are initiated and followed in
  a realistic corona and solar wind using the MAS MHD code, and SEPs
  are modeled using EPREM, a 3D energetic particle transport code. The
  particles are not truly coupled to the MHD solution, in the sense
  that the electric and magnetic fields from the MHD computation drive
  the solutions of the focused transport equation. We show initial
  comparisons with typical CME observations and SEP data, and discuss
  the strengths and limitations of this approach.

---------------------------------------------------------
Title: Magnetic reconnection driven by filament eruption in the 7
    June 2011 event
Authors: van Driel-Gesztelyi, L.; Baker, D.; Török, T.; Pariat, E.;
   Green, L. M.; Williams, D. R.; Carlyle, J.; Valori, G.; Démoulin,
   P.; Matthews, S. A.; Kliem, B.; Malherbe, J. -M.
2014IAUS..300..502V    Altcode:
  During an unusually massive filament eruption on 7 June 2011,
  SDO/AIA imaged for the first time significant EUV emission around a
  magnetic reconnection region in the solar corona. The reconnection
  occurred between magnetic fields of the laterally expanding CME
  and a neighbouring active region. A pre-existing quasi-separatrix
  layer was activated in the process. This scenario is supported by
  data-constrained numerical simulations of the eruption. Observations
  show that dense cool filament plasma was re-directed and heated in
  situ, producing coronal-temperature emission around the reconnection
  region. These results provide the first direct observational evidence,
  supported by MHD simulations and magnetic modelling, that a large-scale
  re-configuration of the coronal magnetic field takes place during
  solar eruptions via the process of magnetic reconnection.

---------------------------------------------------------
Title: Initiation of Coronal Mass Ejections by Sunspot Rotation
Authors: Valori, G.; Török, T.; Temmer, M.; Veronig, A. M.; van
   Driel-Gesztelyi, L.; Vršnak, B.
2014IAUS..300..201V    Altcode:
  We report observations of a filament eruption, two-ribbon flare, and
  coronal mass ejection (CME) that occurred in Active Region NOAA 10898
  on 6 July 2006. The filament was located South of a strong sunspot that
  dominated the region. In the evolution leading up to the eruption, and
  for some time after it, a counter-clockwise rotation of the sunspot of
  about 30 degrees was observed. We suggest that the rotation triggered
  the eruption by progressively expanding the magnetic field above the
  filament. To test this scenario, we study the effect of twisting
  the initially potential field overlying a pre-existing flux rope,
  using three-dimensional zero-β MHD simulations. We consider a magnetic
  configuration whose photospheric flux distribution and coronal structure
  is guided by the observations and a potential field extrapolation. We
  find that the twisting leads to the expansion of the overlying field. As
  a consequence of the progressively reduced magnetic tension, the flux
  rope quasi-statically adapts to the changed environmental field, rising
  slowly. Once the tension is sufficiently reduced, a distinct second
  phase of evolution occurs where the flux rope enters an unstable regime
  characterized by a strong acceleration. Our simulation thus suggests
  a new mechanism for the triggering of eruptions in the vicinity of
  rotating sunspots.

---------------------------------------------------------
Title: Simulations of Emerging Magnetic Flux. I. The Formation of
    Stable Coronal Flux Ropes
Authors: Leake, James E.; Linton, Mark G.; Török, Tibor
2013ApJ...778...99L    Altcode: 2013arXiv1308.6204L
  We present results from three-dimensional visco-resistive
  magnetohydrodynamic simulations of the emergence of a convection zone
  magnetic flux tube into a solar atmosphere containing a pre-existing
  dipole coronal field, which is orientated to minimize reconnection with
  the emerging field. We observe that the emergence process is capable
  of producing a coronal flux rope by the transfer of twist from the
  convection zone, as found in previous simulations. We find that this
  flux rope is stable, with no evidence of a fast rise, and that its
  ultimate height in the corona is determined by the strength of the
  pre-existing dipole field. We also find that although the electric
  currents in the initial convection zone flux tube are almost perfectly
  neutralized, the resultant coronal flux rope carries a significant
  net current. These results suggest that flux tube emergence is capable
  of creating non-current-neutralized stable flux ropes in the corona,
  tethered by overlying potential fields, a magnetic configuration that
  is believed to be the source of coronal mass ejections.

---------------------------------------------------------
Title: Magnetohydrodynamic Simulations of Interplanetary Coronal
    Mass Ejections
Authors: Lionello, Roberto; Downs, Cooper; Linker, Jon A.; Török,
   Tibor; Riley, Pete; Mikić, Zoran
2013ApJ...777...76L    Altcode:
  We describe a new MHD model for the propagation of interplanetary
  coronal mass ejections (ICMEs) in the solar wind. Accurately following
  the propagation of ICMEs is important for determining space weather
  conditions. Our model solves the MHD equations in spherical coordinates
  from a lower boundary above the critical point to Earth and beyond. On
  this spherical surface, we prescribe the magnetic field, velocity,
  density, and temperature calculated typically directly from a coronal
  MHD model as time-dependent boundary conditions. However, any model
  that can provide such quantities either in the inertial or rotating
  frame of the Sun is suitable. We present two validations of the
  technique employed in our new model and a more realistic simulation
  of the propagation of an ICME from the Sun to Earth.

---------------------------------------------------------
Title: Initiation of Coronal Mass Ejections by Sunspot Rotation
Authors: Török, T.; Temmer, M.; Valori, G.; Veronig, A. M.; van
   Driel-Gesztelyi, L.; Vršnak, B.
2013SoPh..286..453T    Altcode: 2014arXiv1401.2922T
  We study a filament eruption, two-ribbon flare, and coronal mass
  ejection (CME) that occurred in NOAA Active Region 10898 on 6 July
  2006. The filament was located South of a strong sunspot that dominated
  the region. In the evolution leading up to the eruption, and for some
  time after it, a counter-clockwise rotation of the sunspot of about
  30 degrees was observed. We suggest that the rotation triggered the
  eruption by progressively expanding the magnetic field above the
  filament. To test this scenario, we study the effect of twisting
  the initially potential field overlying a pre-existing flux-rope,
  using three-dimensional zero-β MHD simulations. We first consider
  a relatively simple and symmetric system, and then study a more
  complex and asymmetric magnetic configuration, whose photospheric-flux
  distribution and coronal structure are guided by the observations and a
  potential field extrapolation. In both cases, we find that the twisting
  leads to the expansion of the overlying field. As a consequence of the
  progressively reduced magnetic tension, the flux-rope quasi-statically
  adapts to the changed environmental field, rising slowly. Once the
  tension is sufficiently reduced, a distinct second phase of evolution
  occurs where the flux-rope enters an unstable regime characterised by
  a strong acceleration. Our simulations thus suggest a new mechanism
  for the triggering of eruptions in the vicinity of rotating sunspots.

---------------------------------------------------------
Title: Modeling Solar Eruptions: Where Do We stand?
Authors: Torok, Tibor
2013SPD....4430101T    Altcode:
  Solar flares and coronal mass ejections involve massive releases of
  energies into the heliosphere and are the main driver of space weather
  disturbances near Earth. It is now well accepted that these enigmatic
  events are manifestations of a sudden and violent disruption of the
  Sun's coronal magnetic field. However, although such eruptions have
  been studied for many years, the detailed physical mechanisms by which
  they are initiated and driven are not yet fully understood; primarily
  because of our present inability to accurately measure magnetic fields
  in the corona. Numerical models have become a powerful tool to help us
  overcome this limitation. Global simulations of solar eruptions are
  particularly challenging, because of the enormous disparity of the
  relevant scales. While the steady advance of computational power has
  enabled us to model eruptions with ever increasing detail and realism,
  many questions remain unanswered. In this talk, I review what we have
  learned from numerical modeling about the physical processes associated
  with solar eruptions and I will discuss the current limitations and
  future prospects of models.

---------------------------------------------------------
Title: The challenge in making models of fast CMEs
Authors: Mikić, Zoran; Török, Tibor; Titov, Viacheslav; Linker,
   Jon A.; Lionello, Roberto; Downs, Cooper; Riley, Pete
2013AIPC.1539...42M    Altcode:
  It has been a challenge to explain theoretically how fast CMEs
  (exceeding ~ 1,000km/s) occur. Our numerical models suggest that it
  is not easy to release enough magnetic energy impulsively from an
  active region. We have been studying CME models that are constrained
  by observed magnetic fields, with realistic coronal plasma density
  and temperature profiles, as derived from thermodynamic models of
  the corona. We find that to get fast CMEs, the important parameters
  are the magnetic energy density, the magnetic field drop-off index,
  and the Alfvén speed profile in active regions. We describe how we
  energize active regions, and how we subsequently initiate CMEs via
  flux cancellation. We contrast CMEs from idealized zero-beta models
  with more sophisticated models based on thermodynamic solutions.

---------------------------------------------------------
Title: Which magnetic topologies are favorable for an efficient
    acceleration and escape of SEPs?
Authors: Titov, Viacheslav S.; Linker, Jon A.; Mikić, Zoran; Török,
   Tibor; Lionello, Roberto
2013shin.confE.129T    Altcode:
  We assume that unstable magnetic flux ropes are the drivers of solar
  flares and CMEs producing SEPs. The natural sites for the acceleration
  of SEPs are current sheets and shocks that are formed in the solar
  corona around these flux ropes during their eruptions. The location of
  the current sheets and shocks in turn depends on the structure of the
  background magnetic field ambient to the erupting flux ropes. This
  raises an important question on which topologies of the background
  field are favorable for an efficient production and escape of SEPs. We
  propose that such topologies are inherent to pseudo-streamers, whose
  lobes often harbor magnetic flux ropes. The pseudo-streamers possess
  closed and open separator field lines, where current sheets have to
  be formed whenever the harbored flux ropes start to erupt. These are
  good preconditions for both the acceleration and transport of SEPs in
  the open-field corona. In addition, the pseudo-streamers' structure
  is prone to the generation of sympathetic flux-rope eruptions, which
  can produce widely separated but well-synchronized beams of SEPs.

---------------------------------------------------------
Title: Modeling Solar Eruptions: Where Do We Stand?
Authors: Torok, Tibor
2013AAS...22220001T    Altcode:
  Solar flares and coronal mass ejections involve massive releases of
  energies into the heliosphere and are the main driver of space weather
  disturbances near Earth. It is now well accepted that these enigmatic
  events are manifestations of a sudden and violent disruption of the
  Sun's coronal magnetic field. However, although such eruptions have
  been studied for many years, the detailed physical mechanisms by which
  they are initiated and driven are not yet fully understood; primarily
  because of our present inability to accurately measure magnetic fields
  in the corona. Numerical models have become a powerful tool to help us
  overcome this limitation. Global simulations of solar eruptions are
  particularly challenging, because of the enormous disparity of the
  relevant scales. While the steady advance of computational power has
  enabled us to model eruptions with ever increasing detail and realism,
  many questions remain unanswered. In this talk, I review what we have
  learned from numerical modeling about the physical processes associated
  with solar eruptions and I will discuss the current limitations and
  future prospects of models.

---------------------------------------------------------
Title: Pseudo-Streamer Structures in the 2010 August 1-2 CMEs:
    PFSS verses MHD model.
Authors: Titov, Viacheslav S.; Mikić, Zoran; Török, Tibor; Linker,
   Jon A.; Panasenco, Olga
2013shin.confE.130T    Altcode:
  We upgrade our previous potential field source-surface (PFSS) model of
  the background magnetic field in the 2010 August 1-2 sympathetic CMEs
  to a more accurate thermodynamic MHD model of the solar corona. For
  this new model, we verify our earlier results on the structure of the
  large-scale magnetic field, making a similar topological analysis of the
  field as before. We identify the similarities and differences between
  the two configurations, particularly, for the eruptive regions with
  three pseudo-streamers that we have found before. The new study confirms
  that all these pseudo-streamers indeed contain vertical separatrix
  surfaces located between two adjacent disconnected coronal holes. Of
  special interest to us are the magnetic null points and separator
  field lines belonging to such separatrix surfaces. These topological
  features exist in both PFSS and MHD models, albeit in different
  forms. We reassert our earlier hypothesis that magnetic reconnection
  at these nulls and separators likely plays a key role in establishing
  a physical connection between the successive eruptions observed by
  SDO and STEREO. The results obtained provide further validation of
  our recent simplified MHD model of sympathetic eruptions (Török et
  al. 2011). <P />Work supported by Lockheed Martin, NASA's Heliophysics
  Theory and SR&amp;T programs, and SHINE NSF Grant AGS-1156119.

---------------------------------------------------------
Title: Numerical modeling of fast CMEs from Sun to Earth
Authors: Torok, Tibor; Downs, Cooper; Lionello, Roberto; Linker,
   Jon A.; Titov, Viacheslav S.; Mikic, Zoran; Riley, Pete
2013EGUGA..1512485T    Altcode:
  Coronal mass ejections (CMEs) are the main driver of space weather
  disturbances near Earth. The most severe disturbances are caused
  by fast CMEs with coronal speeds in excess of 1000 km/s and magnetic
  orientations favorable for interaction with the Earth's magnetosphere. A
  proper assessment of the impact of CMEs from numerical simulations
  requires the self-consistent modeling of both CME initiation and
  its propagation through interplanetary space. Such simulations are
  very challenging, in particular because of the enormous disparity of
  scales involved. Here we present our recent attempts to model fast
  CMEs all the way from Sun to Earth. We first simulate the initiation
  and propagation of CMEs in the corona using our "thermodynamic" MHD
  model, which includes empirical coronal heating, thermal conduction,
  and radiation losses. After the initial configuration, consisting of a
  large-scale dipole field and an idealized active region, is relaxed to
  a steady-state solar wind solution, we insert a flux rope in magnetic
  equilibrium into the active region and trigger its eruption by imposing
  localized converging flows. We perform a small series of simulations,
  varying the geometry and field strength of the flux rope. The resulting
  CMEs produce a shock low in the corona and reach peak velocities of
  up to 3000 km/s, after which they slow down to constant propagation
  speeds of 1000 km/s or less. We then use our recently developed
  heliospheric model to simulate the further propagation to 1 AU for
  one of the model CMEs.

---------------------------------------------------------
Title: Can We Predict the Geoeffectiveness of CMEs?
Authors: Linker, Jon; Lionello, Roberto; Downs, Cooper; Mikic, Zoran;
   Torok, Tibor; Titov, Viacheslav; Riley, Pete
2013enss.confE..11L    Altcode:
  Coronal Mass Ejections (CMEs) are immense eruptions of plasma and
  magnetic field that are propelled outward from the sun, sometimes
  with velocities greater than 2000 km/s. They are also responsible for
  some of the most severe space weather at Earth, including geomagnetic
  storms. Modeling CMEs from Sun to Earth is especially challenging,
  because of the enormous disparity of scales involved. At the present
  time, both NOAA SWPC and the CCMC use the WSA-Enlil model with "cone
  model" CMEs to predict the arrival of possibly geoeffective CMEs at
  Earth. This model has no embedded magnetic fields in the CME, and
  therefore does not successfully predict the magnitude and direction
  of Bz. In this paper, we outline a possible approach to this problem,
  using coupled coronal and heliospheric simulations of coronal mass
  ejections. Research supported by NASA, NSF, and AFOSR.

---------------------------------------------------------
Title: Characterizing the Magnetic Topology of Solar Eruptions
Authors: Titov, Viacheslav S.; Mikic, Zoran; Torok, Tibor; Linker,
   Jon A.; Lionello, Roberto; Riley, Pete
2013enss.confE..15T    Altcode:
  Numerical MHD simulations of solar eruptions have made it possible
  to model the evolution of magnetic configurations with considerable
  realism. However, a comprehensive understanding of these complex
  configurations requires the development of sophisticated techniques to
  analyze the three-dimensional magnetic field structure. We describe
  the current state of the art in this kind of analysis, with detailed
  illustrations from on-going projects at Predictive Science. Separatrix
  surfaces and quasi-separatrix layers form a structural skeleton of
  magnetic configurations by dividing them into multiple components
  with a simple topology. We discuss the principles and capabilities
  of our techniques for analyzing the structural skeletons in erupting
  configurations. In particular, we show how these techniques allow one:
  (1) to identify erupting and non-erupting strands of the flux ropes; (2)
  to determine the global topological flux cells in which such flux ropes
  reside, and how they interact in successive eruptions; (3) to calculate
  evolving magnetic fluxes for each component of these configurations;
  (4) to relate certain structural features to observational features,
  such as H-alpha flare ribbons, extreme-ultraviolet dimmings, and X-ray
  sigmoids in solar eruptions. The ability to compare our results with
  observations enables us to verify the accuracy of the MHD models and
  to understand how the coronal magnetic field opens during eruptions.

---------------------------------------------------------
Title: A Multi-spacecraft View of a Giant Filament Eruption during
    2009 September 26/27
Authors: Gosain, Sanjay; Schmieder, Brigitte; Artzner, Guy; Bogachev,
   Sergei; Török, Tibor
2012ApJ...761...25G    Altcode: 2012arXiv1210.6686G
  We analyze multi-spacecraft observations of a giant filament eruption
  that occurred during 2009 September 26 and 27. The filament eruption was
  associated with a relatively slow coronal mass ejection. The filament
  consisted of a large and a small part, and both parts erupted nearly
  simultaneously. Here we focus on the eruption associated with the
  larger part of the filament. The STEREO satellites were separated
  by about 117° during this event, so we additionally used SoHO/EIT
  and CORONAS/TESIS observations as a third eye (Earth view) to aid our
  measurements. We measure the plane-of-sky trajectory of the filament as
  seen from STEREO-A and TESIS viewpoints. Using a simple trigonometric
  relation, we then use these measurements to estimate the true direction
  of propagation of the filament which allows us to derive the true
  R/R <SUB>⊙</SUB>-time profile of the filament apex. Furthermore, we
  develop a new tomographic method that can potentially provide a more
  robust three-dimensional (3D) reconstruction by exploiting multiple
  simultaneous views. We apply this method also to investigate the 3D
  evolution of the top part of filament. We expect this method to be
  useful when SDO and STEREO observations are combined. We then analyze
  the kinematics of the eruptive filament during its rapid acceleration
  phase by fitting different functional forms to the height-time
  data derived from the two methods. We find that for both methods an
  exponential function fits the rise profile of the filament slightly
  better than parabolic or cubic functions. Finally, we confront these
  results with the predictions of theoretical eruption models.

---------------------------------------------------------
Title: Pseudo-Streamer Magnetic Topologies in the 2010 August 1-2 CMEs
Authors: Titov, V. S.; Mikic, Z.; Torok, T.; Linker, J. A.;
   Panasenco, O.
2012AGUFMSH51A2211T    Altcode:
  We upgrade our previous source-surface model of the background magnetic
  field in the 2010 August 1-2 sympathetic CMEs to a more accurate
  thermodynamic MHD model of the solar corona. For this new model,
  we verify our earlier results on the structure of the large-scale
  magnetic field, making a similar topological analysis of the field
  as before. We identify the similarities and differences between the
  two configurations, particularly, for the eruptive regions with three
  pseudo-streamers that we have found before. The new study confirms
  that all these pseudo-streamers indeed contain vertical separatrix
  surfaces located between two adjacent disconnected coronal holes. Of
  special interest to us are the magnetic null points and separator field
  lines belonging to such separatrix surfaces. We reassert our earlier
  hypothesis that magnetic reconnection at these nulls and separators
  likely plays a key role in establishing a physical connection between
  the successive eruptions observed by SDO and STEREO. The results
  obtained provide further validation of our recent simplified MHD
  model of sympathetic eruptions (Török et al. 2011). Work supported
  by NASA's Heliophysics Theory and SR&amp;T programs, and SHINE NSF
  Grant AGS-1156119.

---------------------------------------------------------
Title: Prediction of the Solar Corona for the 2012 November 13 Total
    Solar Eclipse
Authors: Mikic, Z.; Linker, J. A.; Downs, C.; Lionello, R.; Riley,
   P.; Titov, V. S.; Torok, T.
2012AGUFMSH33A2218M    Altcode:
  It has become our tradition to predict the structure of the corona
  prior to eclipses, using a magnetohydrodynamic (MHD) model based on
  measurements of photospheric magnetic fields on the Sun. We plan to
  continue this tradition by predicting the structure of the corona for
  the November 13, 2012 total solar eclipse, using SDO/HMI photospheric
  magnetic field data. We will predict the structure of the corona,
  including images of polarization brightness, magnetic field line traces,
  and images of simulated emission in EUV and X-rays. These images can
  be compared directly with observations of the total eclipse, as well
  as observations from SDO/AIA, Hinode/XRT, and STEREO/EUVI. Research
  supported by NASA's Heliophysics Theory and Living With a Star Programs,
  and NSF/FESD.

---------------------------------------------------------
Title: Using multi-wavelength observations to constrain CME
    simulations
Authors: Torok, T.; Mikic, Z.; Titov, V. S.; Linker, J. A.; Downs,
   C.; Lionello, R.; Riley, P.
2012AGUFMSH33E..01T    Altcode:
  The steady growth of computing power now provides the possibility
  to model coronal mass ejections (CMEs) at different levels of
  complexity. Present CME simulations range from relatively simple
  zero-beta calculations, which consider idealized configurations
  to isolate the basic physical mechanisms at work in CMEs, to
  semi-realistic "thermodynamic" MHD simulations of specific events
  that allow us to confront the model results directly with the
  observations. In this talk, we will discuss the respective benefits
  of these different approaches. As an example, we will consider the
  well-known sympathetic eruptions event on 2010, August 1, which our
  group has been modeling using various degrees of approximation. In
  particular, we will illustrate how we employed the observations (i)
  to set up the respective initial magnetic configurations and (ii)
  to validate the simulation results.

---------------------------------------------------------
Title: Magnetohydrodynamic Simulations of Interplanetary Coronal
    Mass Ejections
Authors: Lionello, R.; Downs, C.; Linker, J. A.; Torok, T.; Mikic, Z.
2012AGUFMSH41B2117L    Altcode:
  Accurately following the propagation of Interplanetary Coronal Mass
  Ejections (ICME) is very important for determining space weather
  conditions. These are known to impact the functioning of satellites
  or create a dangerous environment for astronauts in orbit around the
  Earth. Here we describe how we simulate with our MHD numerical model in
  spherical coordinates the propagation of ICMEs from the critical point
  to Earth and beyond. We first obtain the boundary conditions to apply at
  the lower boundaries using the results of simulations of coronal mass
  ejections. These are normally derived from the coronal version of our
  own model, but any other model that can provide the components of the
  magnetic field and the velocity, density, and pressure of the plasma
  can be used. Then we calculate the propagation of the disturbance in
  interplanetary space.

---------------------------------------------------------
Title: A Parametric Study of Erupting Flux Rope Rotation. Modeling
    the "Cartwheel CME" on 9 April 2008
Authors: Kliem, B.; Török, T.; Thompson, W. T.
2012SoPh..281..137K    Altcode: 2011arXiv1112.3389K; 2012SoPh..tmp...91K
  The rotation of erupting filaments in the solar corona is addressed
  through a parametric simulation study of unstable, rotating flux ropes
  in bipolar force-free initial equilibrium. The Lorentz force due to
  the external shear-field component and the relaxation of tension in the
  twisted field are the major contributors to the rotation in this model,
  while reconnection with the ambient field is of minor importance, due
  to the field's simple structure. In the low-beta corona, the rotation is
  not guided by the changing orientation of the vertical field component's
  polarity inversion line with height. The model yields strong initial
  rotations which saturate in the corona and differ qualitatively from
  the profile of rotation vs. height obtained in a recent simulation of
  an eruption without preexisting flux rope. Both major mechanisms writhe
  the flux rope axis, converting part of the initial twist helicity,
  and produce rotation profiles which, to a large part, are very similar
  within a range of shear-twist combinations. A difference lies in the
  tendency of twist-driven rotation to saturate at lower heights than
  shear-driven rotation. For parameters characteristic of the source
  regions of erupting filaments and coronal mass ejections, the shear
  field is found to be the dominant origin of rotations in the corona
  and to be required if the rotation reaches angles of order 90 degrees
  and higher; it dominates even if the twist exceeds the threshold of
  the helical kink instability. The contributions by shear and twist to
  the total rotation can be disentangled in the analysis of observations
  if the rotation and rise profiles are simultaneously compared with
  model calculations. The resulting twist estimate allows one to judge
  whether the helical kink instability occurred. This is demonstrated
  for the erupting prominence in the "Cartwheel CME" on 9 April 2008,
  which has shown a rotation of ≈ 115<SUP>∘</SUP> up to a height of
  1.5 R<SUB>⊙</SUB> above the photosphere. Out of a range of initial
  equilibria which include strongly kink-unstable (twist Φ=5π), weakly
  kink-unstable (Φ=3.5π), and kink-stable (Φ=2.5π) configurations,
  only the evolution of the weakly kink-unstable flux rope matches the
  observations in their entirety.

---------------------------------------------------------
Title: 2010 August 1-2 Sympathetic Eruptions. I. Magnetic Topology
    of the Source-surface Background Field
Authors: Titov, V. S.; Mikic, Z.; Török, T.; Linker, J. A.;
   Panasenco, O.
2012ApJ...759...70T    Altcode: 2012arXiv1209.5797T
  A sequence of apparently coupled eruptions was observed on 2010 August
  1-2 by Solar Dynamics Observatory and STEREO. The eruptions were closely
  synchronized with one another, even though some of them occurred at
  widely separated locations. In an attempt to identify a plausible reason
  for such synchronization, we study the large-scale structure of the
  background magnetic configuration. The coronal field was computed from
  the photospheric magnetic field observed at the appropriate time period
  by using the potential field source-surface model. We investigate the
  resulting field structure by analyzing the so-called squashing factor
  calculated at the photospheric and source-surface boundaries, as well as
  at different coronal cross-sections. Using this information as a guide,
  we determine the underlying structural skeleton of the configuration,
  including separatrix and quasi-separatrix surfaces. Our analysis
  reveals, in particular, several pseudo-streamers in the regions where
  the eruptions occurred. Of special interest to us are the magnetic
  null points and separators associated with the pseudo-streamers. We
  propose that magnetic reconnection triggered along these separators
  by the first eruption likely played a key role in establishing the
  assumed link between the sequential eruptions. The present work
  substantiates our recent simplified magnetohydrodynamic model of
  sympathetic eruptions and provides a guide for further deeper study
  of these phenomena. Several important implications of our results for
  the S-web model of the slow solar wind are also addressed.

---------------------------------------------------------
Title: Contracting and Erupting Components of Sigmoidal Active Regions
Authors: Liu, Rui; Liu, Chang; Török, Tibor; Wang, Yuming; Wang,
   Haimin
2012ApJ...757..150L    Altcode: 2012arXiv1208.0640L
  It has recently been noted that solar eruptions can be associated with
  the contraction of coronal loops that are not involved in magnetic
  reconnection processes. In this paper, we investigate five coronal
  eruptions originating from four sigmoidal active regions, using
  high-cadence, high-resolution narrowband EUV images obtained by the
  Solar Dynamic Observatory (SDO). The magnitudes of the flares associated
  with the eruptions range from GOES class B to class X. Owing to the
  high-sensitivity and broad temperature coverage of the Atmospheric
  Imaging Assembly (AIA) on board SDO, we are able to identify both the
  contracting and erupting components of the eruptions: the former is
  observed in cold AIA channels as the contracting coronal loops overlying
  the elbows of the sigmoid, and the latter is preferentially observed
  in warm/hot AIA channels as an expanding bubble originating from the
  center of the sigmoid. The initiation of eruption always precedes the
  contraction, and in the energetically mild events (B- and C-flares),
  it also precedes the increase in GOES soft X-ray fluxes. In the more
  energetic events, the eruption is simultaneous with the impulsive phase
  of the nonthermal hard X-ray emission. These observations confirm that
  loop contraction is an integrated process in eruptions with partially
  opened arcades. The consequence of contraction is a new equilibrium with
  reduced magnetic energy, as the contracting loops never regain their
  original positions. The contracting process is a direct consequence of
  flare energy release, as evidenced by the strong correlation of the
  maximal contracting speed, and strong anti-correlation of the time
  delay of contraction relative to expansion, with the peak soft X-ray
  flux. This is also implied by the relationship between contraction
  and expansion, i.e., their timing and speed.

---------------------------------------------------------
Title: Slow Rise and Partial Eruption of a Double-decker
    Filament. I. Observations and Interpretation
Authors: Liu, Rui; Kliem, Bernhard; Török, Tibor; Liu, Chang; Titov,
   Viacheslav S.; Lionello, Roberto; Linker, Jon A.; Wang, Haimin
2012ApJ...756...59L    Altcode: 2012arXiv1207.1757L
  We study an active-region dextral filament that was composed of
  two branches separated in height by about 13 Mm, as inferred from
  three-dimensional reconstruction by combining SDO and STEREO-B
  observations. This "double-decker" configuration sustained for days
  before the upper branch erupted with a GOES-class M1.0 flare on 2010
  August 7. Analyzing this evolution, we obtain the following main
  results. (1) During the hours before the eruption, filament threads
  within the lower branch were observed to intermittently brighten up,
  lift upward, and then merge with the upper branch. The merging process
  contributed magnetic flux and current to the upper branch, resulting
  in its quasi-static ascent. (2) This transfer might serve as the
  key mechanism for the upper branch to lose equilibrium by reaching
  the limiting flux that can be stably held down by the overlying
  field or by reaching the threshold of the torus instability. (3)
  The erupting branch first straightened from a reverse S shape that
  followed the polarity inversion line and then writhed into a forward S
  shape. This shows a transfer of left-handed helicity in a sequence of
  writhe-twist-writhe. The fact that the initial writhe is converted into
  the twist of the flux rope excludes the helical kink instability as the
  trigger process of the eruption, but supports the occurrence of the
  instability in the main phase, which is indeed indicated by the very
  strong writhing motion. (4) A hard X-ray sigmoid, likely of coronal
  origin, formed in the gap between the two original filament branches
  in the impulsive phase of the associated flare. This supports a model
  of transient sigmoids forming in the vertical flare current sheet. (5)
  Left-handed magnetic helicity is inferred for both branches of the
  dextral filament. (6) Two types of force-free magnetic configurations
  are compatible with the data, a double flux rope equilibrium and a
  single flux rope situated above a loop arcade.

---------------------------------------------------------
Title: Reconstruction of 3D Coronal Magnetic Structures from
    THEMIS/MTR and Hinode/SOT Vector Maps
Authors: Schmieder, B.; Guo, Y.; Aulanier, G.; Démoulin, P.; Török,
   T.; Bommier, V.; Wiegelmann, T.; Gosain, S.
2012ASPC..454..363S    Altcode:
  Coordinated campaigns using THEMIS, Hinode, and other instruments have
  allowed us to study the magnetic fields of faculae, filaments, and
  active regions. In a first case, we modelled the 3D magnetic field in a
  flaring active region with a nonlinear force-free field extrapolation,
  using magnetic vectors observed by THEMIS/MTR as boundary condition. In
  order to construct a consistent bottom boundary for the model, we
  first removed the 180 degree ambiguity of the transverse fields and
  minimized the force and torque in the observed vector fields. We found
  a twisted magnetic flux rope, well aligned with the polarity inversion
  line and a part of an Hα filament, and located where a large flare is
  initiated about two hours later. In a second case, Hinode/SOT allowed
  us to detect fine flux concentrations in faculae, while MTR provided us
  with magnetic information at different levels in the atmosphere. The
  polarimetry analysis of the MTR and SOT data gave consistent results,
  using both UNNOFIT and MELANIE inversion codes.

---------------------------------------------------------
Title: MHD modeling of the solar corona: Progress and challenges
Authors: Linker, Jon; Mikic, Zoran; Lionello, Roberto; Riley, Pete;
   Titov, Viacheslav; Torok, Tibor
2012cosp...39.1090L    Altcode: 2012cosp.meet.1090L
  The Sun and its activity is the ultimate driver of space weather at
  Earth. This influence occurs not only via eruptive phenomena such as
  coronal mass ejections, but also through the structure of the corona
  itself, which forms the genesis of fast solar wind streams that trigger
  recurrent geomagnetic activity. Coronal structure also determines the
  connection of the ambient interplanetary magnetic field to CME-related
  shocks and impulsive solar flares, and thus controls where solar
  energetic particles propagate. In this talk we describe both the
  present state of the art and new directions in coronal modeling for
  both dynamic and slowly varying phenomena. We discuss the challenges to
  incorporating these capabilities into future space weather forecasting
  and specification models. Supported by NASA through the HTP, LWS,
  and SR&amp;T programs, by NSF through the FESD and CISM programs,
  and by the AFOSR Space Science program.

---------------------------------------------------------
Title: Magnetic Topology of Pseudo-Streamers in the 2010 August 1-2
    Eruption Events
Authors: Titov, Viacheslav S.; Mikic, Zoran; Torok, Tibor; Linker,
   Jon A.; Panasenco, Olga
2012shin.confE.160T    Altcode:
  A sequence of apparently coupled eruptions was observed on 2010 August
  1-2 by SDO and STEREO. The eruptions were closely synchronized, even
  though some of them occurred very far from each other. Trying to
  identify a plausible reason for such synchronization, we study the
  large-scale structure of the background magnetic field. The latter
  was computed from the photospheric magnetic field observed at the
  appropriate time period by using the potential field source-surface
  model.For the resulting configuration, we determine its structural
  skeleton, which includes all separatrix and quasi-separatrix
  surfaces. Analyzing them, we reveal three pseudo-streamers in the
  regions where the eruptions occurred. Of special interest to us are
  the magnetic null points and separator field lines associated with
  these pseudo-streamers. We propose that magnetic reconnection at
  such nulls and separators played likely a key role in establishing
  the physical link between the successive eruptions. Work supported
  by NASA's Heliophysics Theory and SR&amp;T programs, and SHINE NSF
  Grant AGS-1156119.

---------------------------------------------------------
Title: Sympathetic Eruptive Events and Pseudostreamers
Authors: Panasenco, Olga; Titov, Viacheslav; Mikić, Zoran; Török,
   Tibor; de Toma, Giuliana; Velli, Marco
2012shin.confE.162P    Altcode:
  Sequences of apparently coupled CMEs triggered by sympathetic eruptions
  of solar filaments are usually observed when the initial coronal
  magnetic configuration above the source region contains at least
  one coronal pseudostreamer. We study in detail an example of such a
  sympathetic event observed on 27-28 July 2011 by SDO and STEREO. This
  involved five filaments and caused four individual filament eruptions
  and one partial eruption. The eruptions were closely synchronized,
  even though some occurred at widely separated locations. In an attempt
  to identify a plausible reason of such a synchronization, we study the
  large-scale structure of the background PFSS magnetic fields, computed
  from the observed photospheric magnetic field (SDO/HMI) during the
  appropriate time period. We investigate the magnetic connectivities in
  these configurations by calculating and analyzing the distributions of
  the so-called squashing factor at the photospheric and source-surface
  boundaries, as well as other cross-sections at different heights. This
  allows us to get a comprehensive understanding of the underlying
  structural skeleton of the magnetic configuration. In particular,
  our analysis reveals two pseudostreamer magnetic configurations in the
  region where the eruptions occurred. Of special interest to us are the
  magnetic null points and separators located at the intersection of the
  separatrix domes and curtains of the pseudostreamers. We assume that
  magnetic reconnection induced by the first eruption at these locations
  played likely a major role in establishing the postulated link between
  the different eruptions in sequence. The close relationship between the
  sympathetic eruptions and pseudostreamer configurations are supported
  by a statistical study covering the SDO era (2010-2012).

---------------------------------------------------------
Title: The slow rise phase preceding solar eruptions
Authors: Torok, Tibor
2012shin.confE.214T    Altcode:
  The eruption of active region filaments and quiescent prominences
  is oftenpreceded by a pre-eruptive phase, during which the filament
  or prominencerises slowly for minutes to hours (at a speed of about
  1-10 km/s) beforeit rapidly accelerates and becomes ejected from the
  Sun. Limb observationsof quiescent prominences have shown that their
  pre-eruptive rise is typicallyaccompanied by the slow expansion of
  the surrounding cavity, during which theprominence/cavity system may
  undergo morphological changes.The physics underlying this pre-eruptive
  evolution is not yet well understood.It seems likely that we are
  observing signatures of a magnetic flux rope which,presumably driven
  by slow reconnection, is about to approach a critical heightat which
  it cannot longer remain stable and therefore erupts.In this talk,
  I will further detail this scenario, and I will briefly presenta
  number of eruption simulations that include the pre-eruptive phase,
  with theaim of motivating a discussion on how such simulations may
  help us to interpret the observations.

---------------------------------------------------------
Title: Global energy diagnostics, current sheet formation and
    reconnection outflow jets in a thermodynamic 3D MHD CME simulation
Authors: Reeves, Kathy; Mikić, Zoran; Linker, Jon; Török, Tibor;
   Murphy, Nick
2012shin.confE..40R    Altcode:
  We model a CME using a 3D numerical MHD code that includes coronal
  heating, thermal conduction and radiative cooling in the energy
  equation. We first develop a global coronal solution (from 1 to 20
  Rs) to serve as the initial condition for the CME simulation. The
  magnetic flux distribution at 1 Rs consists of a local subsurface
  dipole superimposed on global dipole, to mimic the presence of an
  active region within the global corona. The resulting configuration
  has solar wind emanating from the open field regions, dense plasma in
  the streamer belt, and hot plasma in the active region. We introduce
  transverse electric fields near the neutral line in the active
  region to form a flux rope, then a converging flow is imposed that
  causes the eruption. We examine the global energy budget for this
  simulated eruption, including the magnetic, kinetic, internal and
  gravitational potential energies, coronal heating, ohmic heating,
  flow of Poynting flux across the simulation boundaries, and losses due
  to radiation. These diagnostic are useful in assessing whether such
  simulations reproduce the characteristics of CME observations. We also
  follow the formation and evolution of the current sheet and reconnection
  outflow jets in this model.

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Title: Observation &amp; Modeling of An Erupting Double-Decker
    Filament
Authors: Liu, Rui; Kliem, B.; Toeroek, T.; Liu, C.; Titov, V. S.;
   Lionello, R.; Linker, J. A.; Wang, H.
2012AAS...22032203L    Altcode:
  We study an active-region dextral filament which was composed of two
  branches separated in height by about 13 Mm. This “double-decker”
  configuration sustained for days before the upper branch erupted on
  2010 August 7. Main results are as follows. 1) During hours before
  the eruption, filament threads within the lower branch were observed
  to intermittently brighten up, lift upward, and then merge with the
  upper branch. The merging process contributed magnetic flux to the
  upper branch, resulting in its quasi-static ascent. 2) This flux
  transfer might serve as the key mechanism for the upper branch to
  lose equilibrium by reaching the limiting flux that can be stably held
  down by the overlying field or by reaching the threshold of the torus
  instability. 3) The erupting branch first straightened from a reverse S
  shape that followed the polarity <P />inversion line and then writhed
  into a forward S shape. This shows a transfer of left-handed helicity
  in a sequence of writhe-twist-writhe. The fact that the initial writhe
  is converted into the twist of the flux rope excludes the helical
  kink instability as the trigger process of the eruption, but allows
  for a role of the instability in the main phase. 4) A hard X-ray
  sigmoid, likely of coronal origin, formed in the gap between the two
  original filament branches in the impulsive phase of the associated
  flare. This supports a model of transient sigmoids forming in the
  vertical flare current sheet. 5) Using MHD modeling, we demonstrate
  that a configuration with two force-free flux ropes of like handedness
  can form in the slow-rise phase before an eruption and that it admits
  stable equilibria as well as the instability of only the upper rope.

---------------------------------------------------------
Title: Observations and simulations of the sympathetic eruptions on
    2010 August 1
Authors: Torok, T.; Mikic, Z.; Panasenco, O.; Titov, V. S.; Reeves,
   K. K.; Velli, M.; Linker, J. A.; de Toma, G.
2012EGUGA..14.3270T    Altcode:
  During the rise of the new solar cycle, the Sun has produced a number
  of so-called sympathetic eruptions, i.e., eruptions that occur close in
  time in different source regions. While it has become clear in recent
  years that in many of such events the individual eruptions must be
  magnetically connected, the exact nature of these connections is not
  yet understood. A particularly beautiful case, which consisted of half
  a dozen individual eruptions, was observed by STEREO and SDO on 2010
  August 1. Here we focus on a subset of two large, consecutive filament
  eruptions that were preceded by a nearby CME. We first summarize the
  main features of these events and then present 3D MHD simulations
  that were designed to model such a chain of eruptions. The simulations
  suggest that the two filament eruptions were triggered by two successive
  reconnection events, each of which was induced by the previous eruption,
  and thus provide a new mechanism for sympathetic eruptions.

---------------------------------------------------------
Title: Global MHD Models of the Corona and Solar Wind
Authors: Mikic, Z.; Linker, J. A.; Lionello, R.; Riley, P.; Titov,
   V. S.; Torok, T.
2012decs.confE..85M    Altcode:
  Magnetohydrodynamic (MHD) models are useful in understanding the
  properties of the global solar corona. They typically use measured
  photospheric magnetic fields and an empirical specification of coronal
  heating. Comparisons of simulated EUV and X-ray emission from such
  models with observations (such as SOHO/EIT, Hinode/XRT, STEREO/EUVI, and
  SDO/AIA) can provide a tight constraint on coronal heating models. We
  will describe how these models can be used to improve our understanding
  of the process that heats the corona.

---------------------------------------------------------
Title: 3D Reconstruction of a Rotating Erupting Prominence
Authors: Thompson, W. T.; Kliem, B.; Török, T.
2012SoPh..276..241T    Altcode: 2011arXiv1112.3388T
  A bright prominence associated with a coronal mass ejection (CME)
  was seen erupting from the Sun on 9 April 2008. This prominence was
  tracked by both the Solar Terrestrial Relations Observatory (STEREO)
  EUVI and COR1 telescopes, and was seen to rotate about the line of
  sight as it erupted; therefore, the event has been nicknamed the
  "Cartwheel CME." The threads of the prominence in the core of the
  CME quite clearly indicate the structure of a weakly to moderately
  twisted flux rope throughout the field of view, up to heliocentric
  heights of 4 solar radii. Although the STEREO separation was 48°,
  it was possible to match some sharp features in the later part of the
  eruption as seen in the 304 Å line in EUVI and in the Hα-sensitive
  bandpass of COR1 by both STEREO Ahead and Behind. These features could
  then be traced out in three-dimensional space, and reprojected into
  a view in which the eruption is directed toward the observer. The
  reconstructed view shows that the alignment of the prominence to the
  vertical axis rotates as it rises up to a leading-edge height of ≈
  2.5 solar radii, and then remains approximately constant. The alignment
  at 2.5 solar radii differs by about 115° from the original filament
  orientation inferred from Hα and EUV data, and the height profile
  of the rotation, obtained here for the first time, shows that two
  thirds of the total rotation are reached within ≈ 0.5 solar radii
  above the photosphere. These features are well reproduced by numerical
  simulations of an unstable moderately twisted flux rope embedded in
  external flux with a relatively strong shear field component.

---------------------------------------------------------
Title: MHD Modeling of the Sympathetic Eruptions Observed on August
    1, 2010
Authors: Mikic, Z.; Torok, T.; Titov, V. S.; Linker, J. A.; Lionello,
   R.; Riley, P.
2011AGUFMSH41B..04M    Altcode:
  The multiple solar eruptions observed by SDO on August 1, 2010 present a
  special challenge to theoretical models of CME initiation. SDO captured
  in detail a remarkable chain of sympathetic eruptions that involved
  the entire visible hemisphere of the Sun (Schrijver et al. 2011). It
  consisted of several flares and six filament eruptions/CMEs, and
  triggered a geomagnetic storm on August 3 (de Toma et al. 2010). This
  series of eruptions was also observed by the two STEREO spacecraft. This
  collection of observations presents a unique opportunity to understand
  sympathetic eruptions theoretically. We will present 3D MHD simulations
  of these events that have helped us to understand the possible
  mechanisms by which the various filament eruptions/CMEs may be linked,
  with particular emphasis on the global topology of the coronal magnetic
  field in which these structures are embedded.

---------------------------------------------------------
Title: Comparing MHD Simulations of the Solar Corona and the Solar
    Wind with Data
Authors: Lionello, R.; Linker, J. A.; Mikic, Z.; Riley, P.; Titov,
   V. S.; Torok, T.
2011AGUFMSH41B..02L    Altcode:
  Our global three-dimensional magnetohydrodynamic (MHD) model of the
  solar corona and the solar wind has been extensively used to model
  the properties of the magnetic field and of the plasma, from Sun
  to Earth and beyond. The key observational input to the model is the
  incorporation of observed photospheric magnetic fields into the boundary
  conditions. We have studied the geometrical and topological properties
  of the magnetic field (e.g., the location and evolution of corona holes,
  the reproduction of streamer structure, the location of the heliospheric
  current sheet, etc.) and its dynamical reconfiguration (e.g., eruptions
  and CMEs propagation). Direct comparison with observations have been
  made in the corona by calculation of emission in several EUV and X-ray
  bands, both for loops and the global corona. We have also compared the
  simulated speed, density, temperature, and magnetic field in the solar
  wind with in situ observations. We will discuss the insights obtained
  on the strengths and limitations of the models from these comparisons.

---------------------------------------------------------
Title: How do Heliospheric Remote-Sensing Observations Limit Magnetic
    Flux Rope Models?
Authors: Riley, P.; Torok, T.; Mikic, Z.; Linker, J. A.; Lionello,
   R.; Titov, V. S.
2011AGUFMSH24A..02R    Altcode:
  In-situ measurements of coronal mass ejecta (CMEs) display a range of
  properties, only some of which can be accounted for by current global
  MHD models. In fact, first-principle models that include the initiation
  and eruption of the ejecta necessarily produce well-defined flux ropes,
  whereas only a fraction of CMEs observed in-situ appear to contain a
  flux rope. In this talk, we summarize our current understanding of
  the observed properties of interplanetary flux ropes and ejecta in
  general. We explore ideas that the dichotomy between CMEs and flux
  ropes might be due to: (1) an observational selection effect, that is,
  all CMEs do in fact contain flux ropes and that the trajectory of the
  spacecraft through the event is what determines whether a flux rope is
  also encountered; (2) interactions of an erupting flux rope with itself
  or between neighboring flux ropes to produce complex structures in which
  the flux-rope structure has been significantly modified or destroyed;
  (3) an evolutionary process, such as relaxation to a low plasma-beta
  state, which governs whether a flux rope is present or not; or (4)
  the existence of two (or more) intrinsic mechanisms for producing CMEs,
  some of which produce flux ropes and some that do not. To assess these
  ideas, we compare model results with a selection of CMEs observed by
  the Ulysses, ACE, and STEREO spacecraft.

---------------------------------------------------------
Title: Advances in Modeling the initiation and evolution of CMEs
    through the Solar WInd
Authors: Riley, P.; Mikic, Z.; Linker, J. A.; Torok, T.; Lionello,
   R.; Titov, V. S.
2011AGUFMSH53C..05R    Altcode:
  Over the last decade, several factors have led to remarkable gains
  in our ability to realistically model a coronal mass ejection (CME)
  all the way from the solar surface to 1 AU, or beyond. First,
  global models of the ambient solar corona and inner heliosphere
  have improved dramatically. The algorithms have transitioned from
  simple polytropic prescriptions to rich thermodynamic models that
  can reproduce the essential features of remote solar observations and
  in-situ measurements. Second, theories of CME initiation, and their
  implementation into numerical models, have developed to the point
  that a range of complex mechanisms can now be simulated with great
  fidelity. Third, the original serial codes are now fully parallelized
  allowing them to recruit thousands of processors, and with this,
  the ability to simulate events on unprecedented temporal and spatial
  scales. And fourth, successive NASA-led missions are returning ever-more
  resolved and accurate photospheric magnetic field observations from
  which boundary conditions can be derived. In this talk, we show how
  these factors have allowed us to produce event-specific simulations
  that provide genuine insight into the initiation and evolution of
  CMEs, and contrast these results with what was "state-of-the-art"
  only 10 years ago. We close by speculating on what the next advances
  in global CME models might be.

---------------------------------------------------------
Title: Magnetic Topology of the Sympathetic CMEs Observed on 27 July
    2011 and 1 August 2010
Authors: Titov, V. S.; Mikic, Z.; Torok, T.; Linker, J. A.;
   Panasenco, O.
2011AGUFMSH43B1949T    Altcode:
  Two fascinating sequences of apparently coupled CMEs were observed
  on 27-28 July 2011 and 1-2 August 2010 by SDO and STEREO. The latter
  sequence has recently been described at length by Schrijver &amp;
  Title (2011). In both CME sequences, the individual eruptions were
  closely synchronized with one another, even though some of them
  occurred at widely separated locations. In an attempt to identify a
  plausible reason of such a synchronization, we study the large-scale
  structure of the background PFSS magnetic fields that were computed
  from the observed photospheric magnetic field at the appropriate
  time period. We investigate the magnetic connectivities in these
  configurations by calculating and analyzing the distributions of the
  so-called squashing factor at the photospheric and source-surface
  boundaries, as well as at different cross-sections. This allows us
  to get a comprehensive understanding of the underlying structural
  skeleton of the magnetic configuration. In particular, our analysis
  reveals several pseudo-streamers in the regions where the eruptions
  occurred. Of special interest to us are the magnetic null points and
  separators located at the intersection of the separatrix domes and
  curtains of the pseudo-streamers. We assume that magnetic reconnection
  induced by the first eruption at these locations played likely a major
  role in establishing the postulated link between the eruptions in both
  CME sequences. Our recent simplified MHD model of sympathetic eruptions
  supports this assumption (Török et al. 2011). In the present study,
  we try to further verify it by comparing the background magnetic
  topologies of the two sequences of CMEs. Work supported by NASA and
  the Center for Integrated Space Weather Modeling (an NSF Science and
  Technology Center).

---------------------------------------------------------
Title: Evolution of Electric Currents during Active Region Formation
Authors: Torok, T.; Archontis, V.; Titov, V. S.
2011AGUFMSH33C..08T    Altcode:
  In previous work it has been shown that the emergence of twisted
  magnetic flux tubes into the corona can lead to the formation of
  both stable and eruptive coronal flux ropes, either by the rigid
  emergence of the tube or by shear flows and reconnection occurring
  within its expanding upper part. Such an intrusion of new magnetic
  flux into the corona naturally produces return currents that flow
  in the opposite direction of the flux rope current. It has been
  argued that such return currents significantly change the local force
  balance -- thus could prevent the flux rope from eruption -- and that
  therefore coronal flux rope models that employ a non-neutralized flux
  rope current are not suitable to model filament eruptions or coronal
  mass ejections. Recently, however, Georgoulis et al. have shown from
  observations that strong non-neutralized currents can exist close
  to the polarity inversion lines of active regions, particularly in
  regions that produce eruptions. This raises the question on the physical
  origin of such non-neutralized currents. In this talk, we will present
  results from our investigation of the evolution of photospheric and
  coronal electric currents in the course of the formation of active
  regions and coronal flux ropes, using the flux emergence simulations by
  Archontis et al., and we will discuss the implications of our results
  for coronal eruptions.

---------------------------------------------------------
Title: A Model for Magnetically Coupled Sympathetic Eruptions
Authors: Török, T.; Panasenco, O.; Titov, V. S.; Mikić, Z.; Reeves,
   K. K.; Velli, M.; Linker, J. A.; De Toma, G.
2011ApJ...739L..63T    Altcode: 2011arXiv1108.2069T
  Sympathetic eruptions on the Sun have been observed for several decades,
  but the mechanisms by which one eruption can trigger another remain
  poorly understood. We present a three-dimensional MHD simulation that
  suggests two possible magnetic trigger mechanisms for sympathetic
  eruptions. We consider a configuration that contains two coronal flux
  ropes located within a pseudo-streamer and one rope located next to
  it. A sequence of eruptions is initiated by triggering the eruption of
  the flux rope next to the streamer. The expansion of the rope leads
  to two consecutive reconnection events, each of which triggers the
  eruption of a flux rope by removing a sufficient amount of overlying
  flux. The simulation qualitatively reproduces important aspects of the
  global sympathetic event on 2010 August 1 and provides a scenario for
  the so-called twin filament eruptions. The suggested mechanisms are
  also applicable for sympathetic eruptions occurring in other magnetic
  configurations.

---------------------------------------------------------
Title: A filament supported by different magnetic field configurations
Authors: Guo, Y.; Schmieder, B.; Démoulin, P.; Wiegelmann, T.;
   Aulanier, G.; Török, T.; Bommier, V.
2011IAUS..273..328G    Altcode:
  A nonlinear force-free magnetic field extrapolation of vector
  magnetogram data obtained by THEMIS/MTR on 2005 May 27 suggests the
  simultaneous existence of different magnetic configurations within
  one active region filament: one part of the filament is supported by
  field line dips within a flux rope, while the other part is located
  in dips within an arcade structure. Although the axial field chirality
  (dextral) and the magnetic helicity (negative) are the same along the
  whole filament, the chiralities of the filament barbs at different
  sections are opposite, i.e., right-bearing in the flux rope part and
  left-bearing in the arcade part. This argues against past suggestions
  that different barb chiralities imply different signs of helicity of
  the underlying magnetic field. This new finding about the chirality of
  filaments will be useful to associate eruptive filaments and magnetic
  cloud using the helicity parameter in the Space Weather Science.

---------------------------------------------------------
Title: Solar activity due to magnetic complexity of active regions
Authors: Schmieder, Brigitte; Mandrini, Cristina; Chandra, Ramesh;
   Démoulin, Pascal; Török, Tibor; Pariat, Etienne; Uddin, Wahab
2011IAUS..273..164S    Altcode:
  Active regions (ARs), involved in the Halloween events during
  October-November 2003, were the source of unusual activity during
  the following solar rotation. The flares on 18-20 November 2003 that
  occur in the AR NOAA10501 were accompanied by coronal mass ejections
  associated to some particularly geoeffective magnetic clouds. <P />Our
  analysis of the magnetic flux and helicity injection revealed that
  a new emerging bipole and consequent shearing motions continuously
  energized the region during its disk passage. The stored energy was
  eventually released through the interaction of the various systems
  of magnetic loops by several magnetic reconnection events. Active
  events on November 18 (filament eruptions and CMEs) were originated by
  shearing motions along a section of the filament channel that injected
  magnetic helicity with sign opposite to that of the AR. Two homologous
  flares, that occurred on November 20, were apparently triggered by
  different mechanisms as inferred from the flare ribbons evolution
  (filament eruption and CMEs). We studied in detail the behaviour of
  two North-South oriented filaments on November 20 2003. They merged
  and split following a process suggestive of `sling-shot' reconnection
  between two coronal flux ropes. We successfully tested this scenario
  in a 3D MHD simulation that is presented in this paper.

---------------------------------------------------------
Title: A model for sympathetic eruptions
Authors: Torok, Tibor; Panasenco, O.; Titov, V. S.; Mikic, Z.; Velli,
   M.; Linker, J.; De Toma, G.
2011shin.confE.125T    Altcode:
  Apart from single eruptions originating in localized source regions,
  the Sun sometimes produces so-called sympathetic events, which consist
  of several individual eruptions occurring almost simultaneously
  in different source regions. The close temporal correlation of the
  individual eruptions in such events indicates a causal link between
  them, but the mechanisms by which one eruption can trigger another
  one remain largely a mystery. <P />A particularly beautiful example
  of a global sympathetic event was recently observed by the Solar
  Dynamics Observatory (SDO) on 1 August 2010. It included a small
  filament eruption and CME that was shortly after followed by the
  nearby subsequent eruptions of two large adjacent (twin) filaments,
  indicating that these three eruptions were physically connected. A
  coronal potential field extrapolation reveals that the twin filaments
  were located in the lobes of a so-called pseudostreamer prior to
  their eruptions. <P />Here we present a 3D MHD simulation of the
  successive eruption of two magnetic flux ropes in such a pseudostreamer
  configuration. The two eruptions are triggered by the simulated eruption
  of a third flux rope in the vicinity of the pseudostreamer. The
  simulation qualitatively reproduces the CME and subsequent twin
  filament eruption on 1 August 2010 and suggests that these events
  were indeed physically connected. Furthermore, it provides a generic
  scenario for the frequently observed twin filament eruptions in coronal
  pseudostreamers and suggests a mechanism by which such eruptions can
  be triggered in the first place. Our results thus provide an important
  step for a better understanding of sympathetic eruptions.

---------------------------------------------------------
Title: Energetics of a Simulated 3D Eruption Using the PSI MAS Code
Authors: Reeves, Kathy K.; Török, Tibor; Linker, Zoran Mikić Jon
2011shin.confE..17R    Altcode:
  We examine the energy flow in a three-dimensional simulation of a
  coronal mass ejection. The CME is simulated using the Predictive
  Science Inc., MAS code. Various forms of energy are tracked as a
  function of time over the whole simulation volume as the eruption
  progresses. Current sheets are mapped to begin the process of locating
  the site of energy release for the simulated flare. We also simulate
  the response of the 6 EUV channels from the AIA telescopes on SDO
  during the simulated eruption.

---------------------------------------------------------
Title: Structural Skeleton of the Background Magnetic Field During
    Sympathetic Eruptions on 1-2 August 2010
Authors: Titov, Viacheslav S.; Mikić, Zoran; Török, Tibor; Linker,
   Jon A.
2011shin.confE.131T    Altcode:
  The Solar Dynamics Observatory observed on 1-2 August 2010 an
  interesting sequence of coronal mass ejections (CMEs) (Schrijver &amp;
  Title, 2011). These CMEs were closely synchronized with one another,
  even though some of them occurred at remote locations. Therefore,
  it is tempting to assume that these events were causally linked. In
  an attempt to identify a plausible reason of such a link, we study
  a large-scale structure of the background magnetic field that has
  been computed from the observed photospheric magnetic field at the
  appropriate time period. For this purpose, we investigate the respective
  magnetic connectivity in the obtained configuration by calculating
  and analyzing the distributions of the so-called squashing factor at
  the boundaries as well as at different cross-sections. This allows
  us to get a comprehensive understanding of the underlying structural
  skeleton of the magnetic configuration. In particular, we have found
  that five of the six erupting flux ropes were located inside the domes
  of three pseudostreamers adjoint to the active region AR 11094. The
  stalks of the pseudostreamers passed along the fan separatrix surfaces
  emanating upward from the respective magnetic null points. We assume
  that magnetic reconnection at these null points played likely a major
  role in establishing a hypothetical causal link between the indicated
  CMEs. The obtained topological framework provides a solid guide for
  further numerical modeling and analysis of the observational data of
  these events. <P />Work supported by NASA and the Center for Integrated
  Space Weather Modeling (an NSF Science and Technology Center).

---------------------------------------------------------
Title: Actors of the main activity in large complex centres during
    the 23 solar cycle maximum
Authors: Schmieder, B.; Démoulin, P.; Pariat, E.; Török, T.;
   Molodij, G.; Mandrini, C. H.; Dasso, S.; Chandra, R.; Uddin, W.;
   Kumar, P.; Manoharan, P. K.; Venkatakrishnan, P.; Srivastava, N.
2011AdSpR..47.2081S    Altcode:
  During the maximum of Solar Cycle 23, large active regions had a long
  life, spanning several solar rotations, and produced large numbers of
  X-class flares and CMEs, some of them associated to magnetic clouds
  (MCs). This is the case for the Halloween active regions in 2003. The
  most geoeffective MC of the cycle (Dst = -457) had its source during
  the disk passage of one of these active regions (NOAA 10501) on
  18 November 2003. Such an activity was presumably due to continuous
  emerging magnetic flux that was observed during this passage. Moreover,
  the region exhibited a complex topology with multiple domains of
  different magnetic helicities. The complexity was observed to reach
  such unprecedented levels that a detailed multi-wavelength analysis
  is necessary to precisely identify the solar sources of CMEs and
  MCs. Magnetic clouds are identified using in situ measurements and
  interplanetary scintillation (IPS) data. Results from these two
  different sets of data are also compared.

---------------------------------------------------------
Title: 3d Mhd Simulation Of Sympathetic Eruptions On 1 August 2010
Authors: Torok, Tibor; Panasenco, O.; Titov, V.; Mikic, Z.; Reeves,
   K.; Velli, M.; Linker, J.; de Toma, G.
2011SPD....42.0908T    Altcode: 2011BAAS..43S.0908T
  Apart from single eruptions originating in localized source regions, the
  Sun sometimes produces so-called sympathetic events, which consist of
  <P />several individual eruptions occurring <P />almost simultaneously
  in different source regions. The close temporal vicinity of the
  individual eruptions in such events indicates the <P />existence of
  a causal link between them, but the mechanisms by which one eruption
  can trigger another one remain largely a mystery. A particularly
  beautiful example of a global sympathetic event was recently observed
  by the Solar Dynamics Observatory (SDO) on 1 August 2010. It included
  a small filament eruption and CME that was closely followed by the
  eruptions of two large adjacent (twin) filaments, indicating that these
  three eruptions were physically connected. A coronal potential field
  extrapolation revealed that the twin filaments were located in the
  lobes of a so-called pseudostreamer prior to their eruptions. Here we
  present a 3D MHD simulation of the successive eruption of two magnetic
  flux ropes in such a pseudostreamer configuration. The two eruptions are
  triggered by the simulated eruption of a third flux rope in the vicinity
  of the pseudostreamer. The simulation qualitatively reproduces the CME
  and subsequent twin filament eruption on 1 August 2010 and suggests that
  these events were indeed physically connected. Furthermore, it provides
  a generic scenario for the frequently observed twin filament eruptions
  in coronal pseudostreamers and suggests a mechanism by which such
  eruptions can be triggered in the first place. Our results thus provide
  an important step for a better understanding of sympathetic eruptions.

---------------------------------------------------------
Title: Magnetic Topology of the Source Surface Potential Field on
    1 August 2010
Authors: Titov, Viacheslav; Mikic, Z.; Torok, T.; Linker, J. A.
2011SPD....42.2303T    Altcode: 2011BAAS..43S.2303T
  A sequence of coronal mass ejections was recently observed by the Solar
  Dynamics Observatory (SDO) on 1 August 2010. The events were closely
  synchronized with one another, even though some of them occured at
  rather different locations. Therefore, it is tempting to assume that
  these events were causally linked with each other. In an attempt to
  verify this assumption and identify a plausible reason of such a link,
  we study the topological structure of the source surface potential
  field that has been computed from the observed photospheric magnetic
  field at the appropriate time period. For this purpose, we investigate
  the respective magnetic connectivity in the obtained configuration by
  calculating and analyzing the distributions of the so-called squashing
  factor at the boundaries as well as at different cross-sections. This
  allows us to get a comprehensive understanding of the underlying
  structural skeleton of the magnetic cofiguration and identify the
  robust topological features that likely establish the assumed causal
  link in the indicated events. The obtained topological framework also
  provides a solid guide for further numerical modeling and analysis of
  the observational data of these eruptions.

---------------------------------------------------------
Title: Homologous Flares and Magnetic Field Topology in Active Region
    NOAA 10501 on 20 November 2003
Authors: Chandra, R.; Schmieder, B.; Mandrini, C. H.; Démoulin, P.;
   Pariat, E.; Török, T.; Uddin, W.
2011SoPh..269...83C    Altcode: 2010arXiv1011.1187C; 2010SoPh..tmp..249C
  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 centre
  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 quasi-separatrix 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.

---------------------------------------------------------
Title: A single picture for solar coronal outflows and radio noise
    storms
Authors: Del Zanna, G.; Aulanier, G.; Klein, K. -L.; Török, T.
2011A&A...526A.137D    Altcode:
  We propose a unified interpretation for persistent coronal outflows
  and metric radio noise storms, two phenomena typically observed in
  association with quiescent solar active regions. Our interpretation
  is based on multi-wavelength observations of two such regions as
  they crossed the meridian in May and July 2007. For both regions,
  we observe a persistent pattern of blue-shifted coronal emission in
  high-temperature lines with Hinode/EIS, and a radio noise storm with the
  Nançay Radioheliograph. The observations are supplemented by potential
  and linear force-free extrapolations of the photospheric magnetic
  field over large computational boxes, and by a detailed analysis of
  the coronal magnetic field topology. We find true separatrices in the
  coronal field and null points high in the corona, which are preferential
  locations for magnetic reconnection and electron acceleration. We
  suggest that the continuous growth of active regions maintains a steady
  reconnection across the separatrices at the null point. This interchange
  reconnection occurs between closed, high-density loops in the core of
  the active region and neighbouring open, low-density flux tubes. Thus,
  the reconnection creates strong pressure imbalances which are the main
  drivers of plasma upflows. Furthermore, the acceleration of low-energy
  electrons in the interchange reconnection region sustains the radio
  noise storm in the closed loop areas, as well as weak type III emission
  along the open field lines. For both active regions studied, we find a
  remarkable agreement between the observed places of persistent coronal
  outflows and radio noise storms with their locations as predicted by
  our interpretation.

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Title: Filament Interaction Modeled by Flux Rope Reconnection
Authors: Török, T.; Chandra, R.; Pariat, E.; Démoulin, P.;
   Schmieder, B.; Aulanier, G.; Linton, M. G.; Mandrini, C. H.
2011ApJ...728...65T    Altcode:
  Hα observations of solar active region NOAA 10501 on 2003 November
  20 revealed a very uncommon dynamic process: during the development
  of a nearby flare, two adjacent elongated filaments approached each
  other, merged at their middle sections, and separated again, thereby
  forming stable configurations with new footpoint connections. The
  observed dynamic pattern is indicative of "slingshot" reconnection
  between two magnetic flux ropes. We test this scenario by means
  of a three-dimensional zero β magnetohydrodynamic simulation,
  using a modified version of the coronal flux rope model by Titov
  and Démoulin as the initial condition for the magnetic field. To
  this end, a configuration is constructed that contains two flux
  ropes which are oriented side-by-side and are embedded in an ambient
  potential field. The choice of the magnetic orientation of the flux
  ropes and of the topology of the potential field is guided by the
  observations. Quasi-static boundary flows are then imposed to bring
  the middle sections of the flux ropes into contact. After sufficient
  driving, the ropes reconnect and two new flux ropes are formed,
  which now connect the former adjacent flux rope footpoints of opposite
  polarity. The corresponding evolution of filament material is modeled
  by calculating the positions of field line dips at all times. The dips
  follow the morphological evolution of the flux ropes, in qualitative
  agreement with the observed filaments.

---------------------------------------------------------
Title: Study of solar flares and filament interaction in NOAA 10501
    on 20 November, 2003
Authors: Chandra, R.; Schmieder, B.; Mandrini, C. H.; Démoulin, P.;
   Pariat, E.; Török, T.; Aulanier, G.; Uddin, W.; Linton, M. G.
2011ASInC...2..323C    Altcode:
  We analyze the observations of two flares from NOAA AR 10501 on 20
  November, 2003. The flares are homologous, exhibit four ribbons and
  are located in a quadrupolar magnetic configuration. The evolution
  of the ribbons suggests that the first eruption is triggered by
  "tether cutting" (with subsequent quadrupolar reconnection as in the
  "magnetic breakout" model), whereas the second one is consistent
  with the "magnetic breakout" model. Another interesting feature of
  our observations is the interaction of two filaments elongated in the
  north-south direction. The filaments merge at their central parts and
  afterwards change their orientation to the east-west direction. This
  merging and splitting is closely related to the evolution found in an
  MHD simulation as a result of reconnection between two flux ropes.

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Title: Writhing and rotation of erupting prominences and CMEs
Authors: Torok, T.; Kliem, B.; Thompson, W. T.; Berger, M. A.
2010AGUFMSH43C..01T    Altcode:
  Erupting prominences often exhibit a writhing motion as they rise in
  the corona to become the core of a coronal mass ejection (CME). The
  writhing points towards the presence of a magnetic flux rope whose top
  part rotates about the direction of ascent. Understanding what causes
  the writhing, and which parameters determine its amount, will help
  us to 1) constrain CME initiation models and 2) predict the magnetic
  orientation of CMEs when they hit the Earth. Two mechanisms have been
  suggested to cause significant writhing/rotation in the low corona,
  namely the helical kink instability (KI) and the interaction of the
  shear field component of the ambient coronal field with the flux rope
  current. Here we present the first height profile of the rotation of an
  erupting prominence, obtained from STEREO observations. The prominence
  rotated by about 120 degree from its pre-eruptive orientation, until
  it reached a heliocentric height of about 2.5 solar radii. The data
  are compared to a series of numerical simulations that study the
  corresponding rotation of an erupting magnetic flux rope, by varying
  the initial flux rope twist and the external shear field component. The
  parameter range compatible with the data is constrained by the observed
  rotation-height and height-time profiles. It is found that, for the set
  of geometrical model parameters considered here, the observed strong
  rotation cannot be caused by the KI alone, but requires the presence
  of a shear field component. Moreover, the simulations suggest that the
  contribution of the shear field component was dominant in the observed
  event, indicating that the flux rope was only moderately twisted. We
  also briefly present the first measurements of the evolution of twist
  and writhe in numerical simulations of confined and ejective flux rope
  eruptions, and we discuss the implications of the results for filament
  eruptions and CMEs.

---------------------------------------------------------
Title: Driving Mechanism and Onset Condition of a Confined Eruption
Authors: Guo, Y.; Ding, M. D.; Schmieder, B.; Li, H.; Török, T.;
   Wiegelmann, T.
2010ApJ...725L..38G    Altcode:
  We study a confined eruption accompanied by an M1.1 flare in solar
  active region (AR) NOAA 10767 on 2005 May 27, where a pre-eruptive
  magnetic flux rope was reported in a nonlinear force-free field (NLFFF)
  extrapolation. The observations show a strong writhing motion of the
  erupting structure, suggesting that a flux rope was indeed present
  and converted some of its twist into writhe in the course of the
  eruption. Using the NLFFF extrapolation, we calculate the twist of
  the pre-eruptive flux rope and find that it is in very good agreement
  with thresholds of the helical kink instability found in numerical
  simulations. We conclude that the activation and rise of the flux
  rope were triggered and driven by the instability. Using a potential
  field extrapolation, we also estimate the height distribution of the
  decay index of the external magnetic field in the AR 1 hr prior to the
  eruption. We find that the decay index stays below the threshold for
  the torus instability for a significant height range above the erupting
  flux rope. This provides a possible explanation for the confinement
  of the eruption to the low corona.

---------------------------------------------------------
Title: 3D Study of Solar Eruptions Using SDO and STEREO Observations
Authors: de Toma, G.; Reinard, A. A.; Gibson, S. E.; Burkepile, J.;
   Fan, Y.; Torok, T.
2010AGUFMSH23A1834D    Altcode:
  Combination of data from the recently launched SDO and the two STEREO
  spacecraft -that are now at about 80deg from the Sun-Earth direction-
  offers the unprecedented opportunity to observe simultaneously the
  region where a CME originates and the CME moving outward in the
  plane-of-the-sky. This allows us to compute trajectories for the
  CME and the associated eruptive prominence and, at the same time, to
  study the on-disk CME manifestations such as flares, dimming regions,
  and coronal waves with very high spatial and temporal resolution. We
  present examples of Earth-directed CMEs, when the CME can be traced
  from the Sun to the Earth, that take advantage of this unique satellite
  configuration.

---------------------------------------------------------
Title: Observational and numerical study of the 25 July 2004 event
Authors: Soenen, A.; Jacobs, C.; Poedts, S.; van Driel-Gesztelyi,
   L.; Torok, T.; Lapenta, G.
2010AGUFMSH23B1843S    Altcode:
  We study the 25 July 2004 event. By analyzing SOHO EIT images we
  establish a basic understanding of the large-scale interaction going
  on during this event. Magnetic reconnection between the expanding
  CME and the Southern hemispheric active regions (AR) will connect the
  leading polarities of the two ARs, lead to brightening in the ARs and
  transport CME field line foot points to distant ARs (observable as
  dimming at the foot points).We reproduce the large scale interactions
  during this event using three-dimensional magneto-hydrodynamic (MHD)
  simulations. We superimpose a magnetic source region that resembles
  the SOHO MDI images on a basic wind model. By emerging new flux at the
  centre of this region we initiate a Coronal Mass Ejection (CME). We
  monitor the evolution of this CME and study its interaction with the
  source region.

---------------------------------------------------------
Title: Reconnection of a Kinking Flux Rope Triggering the Ejection
    of a Microwave and Hard X-Ray Source II. Numerical Modeling
Authors: Kliem, B.; Linton, M. G.; Török, T.; Karlický, M.
2010SoPh..266...91K    Altcode: 2010SoPh..tmp..149K; 2010arXiv1007.2147K
  Numerical simulations of the helical (m=1) kink instability of an
  arched, line-tied flux rope demonstrate that the helical deformation
  enforces reconnection between the legs of the rope if modes with two
  helical turns are dominant as a result of high initial twist in the
  range Φ≳6π. Such a reconnection is complex, involving also the
  ambient field. In addition to breaking up the original rope, it can
  form a new, low-lying, less twisted flux rope. The new flux rope is
  pushed downward by the reconnection outflow, which typically forces it
  to break as well by reconnecting with the ambient field. The top part
  of the original rope, largely rooted in the sources of the ambient
  flux after the break-up, can fully erupt or be halted at low heights,
  producing a "failed eruption." The helical current sheet associated with
  the instability is squeezed between the approaching legs, temporarily
  forming a double current sheet. The leg - leg reconnection proceeds
  at a high rate, producing sufficiently strong electric fields that it
  would be able to accelerate particles. It may also form plasmoids, or
  plasmoid-like structures, which trap energetic particles and propagate
  out of the reconnection region up to the top of the erupting flux rope
  along the helical current sheet. The kinking of a highly twisted flux
  rope involving leg - leg reconnection can explain key features of an
  eruptive but partially occulted solar flare on 18 April 2001, which
  ejected a relatively compact hard X-ray and microwave source and was
  associated with a fast coronal mass ejection.

---------------------------------------------------------
Title: Testing magnetofrictional extrapolation with the
    Titov-Démoulin model of solar active regions
Authors: Valori, G.; Kliem, B.; Török, T.; Titov, V. S.
2010A&A...519A..44V    Altcode: 2010arXiv1005.0254V
  We examine the nonlinear magnetofrictional extrapolation scheme
  using the solar active region model by Titov and Démoulin as test
  field. This model consists of an arched, line-tied current channel
  held in force-free equilibrium by the potential field of a bipolar
  flux distribution in the bottom boundary. A modified version with a
  parabolic current density profile is employed here. We find that the
  equilibrium is reconstructed with very high accuracy in a representative
  range of parameter space, using only the vector field in the bottom
  boundary as input. Structural features formed in the interface
  between the flux rope and the surrounding arcade - “hyperbolic
  flux tube” and “bald patch separatrix surface” - are reliably
  reproduced, as are the flux rope twist and the energy and helicity of
  the configuration. This demonstrates that force-free fields containing
  these basic structural elements of solar active regions can be obtained
  by extrapolation. The influence of the chosen initial condition on
  the accuracy of reconstruction is also addressed, confirming that the
  initial field that best matches the external potential field of the
  model quite naturally leads to the best reconstruction. Extrapolating
  the magnetogram of a Titov-Démoulin equilibrium in the unstable
  range of parameter space yields a sequence of two opposing evolutionary
  phases, which clearly indicate the unstable nature of the configuration:
  a partial buildup of the flux rope with rising free energy is followed
  by destruction of the rope, losing most of the free energy.

---------------------------------------------------------
Title: Symmetric Coronal Jets: A Reconnection-controlled Study
Authors: Rachmeler, L. A.; Pariat, E.; DeForest, C. E.; Antiochos,
   S.; Török, T.
2010ApJ...715.1556R    Altcode:
  Current models and observations imply that reconnection is a key
  mechanism for destabilization and initiation of coronal jets. We evolve
  a system described by the theoretical symmetric jet formation model
  using two different numerical codes with the goal of studying the
  role of reconnection in this system. One of the codes is the Eulerian
  adaptive mesh code ARMS, which simulates magnetic reconnection through
  numerical diffusion. The quasi-Lagrangian FLUX code, on the other hand,
  is ideal and able to evolve the system without reconnection. The ideal
  nature of FLUX allows us to provide a control case of evolution without
  reconnection. We find that during the initial symmetric and ideal phase
  of evolution, both codes produce very similar morphologies and energy
  growth. The symmetry is then broken by a kink-like motion of the axis
  of rotation, after which the two systems diverge. In ARMS, current
  sheets formed and reconnection rapidly released the stored magnetic
  energy. In FLUX, the closed field remained approximately constant
  in height while expanding in width and did not release any magnetic
  energy. We find that the symmetry threshold is an ideal property of the
  system, but the lack of energy release implies that the observed kink is
  not an instability. Because of the confined nature of the FLUX system,
  we conclude that reconnection is indeed necessary for jet formation
  in symmetric jet models in a uniform coronal background field.

---------------------------------------------------------
Title: The writhe of helical structures in the solar corona
Authors: Török, T.; Berger, M. A.; Kliem, B.
2010A&A...516A..49T    Altcode: 2010arXiv1004.3918T
  Context. Helicity is a fundamental property of magnetic fields,
  conserved in ideal MHD. In flux rope geometry, it consists of twist and
  writhe helicity. Despite the common occurrence of helical structures
  in the solar atmosphere, little is known about how their shape relates
  to the writhe, which fraction of helicity is contained in writhe,
  and how much helicity is exchanged between twist and writhe when
  they erupt. <BR /> Aims: Here we perform a quantitative investigation
  of these questions relevant for coronal flux ropes. <BR /> Methods:
  The decomposition of the writhe of a curve into local and nonlocal
  components greatly facilitates its computation. We use it to study
  the relation between writhe and projected S shape of helical curves
  and to measure writhe and twist in numerical simulations of flux
  rope instabilities. The results are discussed with regard to filament
  eruptions and coronal mass ejections (CMEs). <BR /> Results: (1) We
  demonstrate that the relation between writhe and projected S shape
  is not unique in principle, but that the ambiguity does not affect
  low-lying structures, thus supporting the established empirical rule
  which associates stable forward (reverse) S shaped structures low
  in the corona with positive (negative) helicity. (2) Kink-unstable
  erupting flux ropes are found to transform a far smaller fraction
  of their twist helicity into writhe helicity than often assumed. (3)
  Confined flux rope eruptions tend to show stronger writhe at low heights
  than ejective eruptions (CMEs). This argues against suggestions that
  the writhing facilitates the rise of the rope through the overlying
  field. (4) Erupting filaments which are S shaped already before the
  eruption and keep the sign of their axis writhe (which is expected if
  field of one chirality dominates the source volume of the eruption),
  must reverse their S shape in the course of the rise. Implications
  for the occurrence of the helical kink instability in such events are
  discussed. (5) The writhe of rising loops can easily be estimated
  from the angle of rotation about the direction of ascent, once the
  apex height exceeds the footpoint separation significantly. <BR />
  Conclusions: Writhe can straightforwardly be computed for numerical
  data and can often be estimated from observations. It is useful in
  interpreting S shaped coronal structures and in constraining models
  of eruptions.

---------------------------------------------------------
Title: Coexisting Flux Rope and Dipped Arcade Sections Along One
    Solar Filament
Authors: Guo, Y.; Schmieder, B.; Démoulin, P.; Wiegelmann, T.;
   Aulanier, G.; Török, T.; Bommier, V.
2010ApJ...714..343G    Altcode:
  We compute the three-dimensional magnetic field of an active
  region in order to study the magnetic configuration of active region
  filaments. The nonlinear force-free field model is adopted to compute
  the magnetic field above the photosphere, where the vector magnetic
  field was observed by THEMIS/MTR on 2005 May 27. We propose a new
  method to remove the 180° ambiguity of the transverse field. Next, we
  analyze the implications of the preprocessing of the data by minimizing
  the total force and torque in the observed vector fields. This step
  provides a consistent bottom boundary condition for the nonlinear
  force-free field model. Then, using the optimization method to compute
  the coronal field, we find a magnetic flux rope along the polarity
  inversion line. The magnetic flux rope aligns well with part of an Hα
  filament, while the total distribution of the magnetic dips coincides
  with the whole Hα filament. This implies that the magnetic field
  structure in one section of the filament is a flux rope, while the
  other is a sheared arcade. The arcade induced a left-bearing filament
  in the magnetic field of negative helicity, which is opposite to the
  chirality of barbs that a flux rope would induce in a magnetic field
  of the same helicity sign. The field strength in the center of the flux
  rope is about 700 G, and the twist of the field lines is ~1.4 turns.

---------------------------------------------------------
Title: Formation of Torus-Unstable Flux Ropes and Electric Currents
    in Erupting Sigmoids
Authors: Aulanier, G.; Török, T.; Démoulin, P.; DeLuca, E. E.
2010ApJ...708..314A    Altcode:
  We analyze the physical mechanisms that form a three-dimensional
  coronal flux rope and later cause its eruption. This is achieved by a
  zero-β magnetohydrodynamic (MHD) simulation of an initially potential,
  asymmetric bipolar field, which evolves by means of simultaneous slow
  magnetic field diffusion and sub-Alfvénic, line-tied shearing motions
  in the photosphere. As in similar models, flux-cancellation-driven
  photospheric reconnection in a bald-patch (BP) separatrix transforms the
  sheared arcades into a slowly rising and stable flux rope. A bifurcation
  from a BP to a quasi-separatrix layer (QSL) topology occurs later on in
  the evolution, while the flux rope keeps growing and slowly rising,
  now due to shear-driven coronal slip-running reconnection, which
  is of tether-cutting type and takes place in the QSL. As the flux
  rope reaches the altitude at which the decay index -∂ln B/∂ln z
  of the potential field exceeds ~3/2, it rapidly accelerates upward,
  while the overlying arcade eventually develops an inverse tear-drop
  shape, as observed in coronal mass ejections (CMEs). This transition
  to eruption is in accordance with the onset criterion of the torus
  instability. Thus, we find that photospheric flux-cancellation and
  tether-cutting coronal reconnection do not trigger CMEs in bipolar
  magnetic fields, but are key pre-eruptive mechanisms for flux ropes to
  build up and to rise to the critical height above the photosphere at
  which the torus instability causes the eruption. In order to interpret
  recent Hinode X-Ray Telescope observations of an erupting sigmoid, we
  produce simplified synthetic soft X-ray images from the distribution
  of the electric currents in the simulation. We find that a bright
  sigmoidal envelope is formed by pairs of J-shaped field lines in the
  pre-eruptive stage. These field lines form through the BP reconnection
  and merge later on into S-shaped loops through the tether-cutting
  reconnection. During the eruption, the central part of the sigmoid
  brightens due to the formation of a vertical current layer in the wake
  of the erupting flux rope. Slip-running reconnection in this layer
  yields the formation of flare loops. A rapid decrease of currents due
  to field line expansion, together with the increase of narrow currents
  in the reconnecting QSL, yields the sigmoid hooks to thin in the early
  stages of the eruption. Finally, a slightly rotating erupting loop-like
  feature (ELLF) detaches from the center of the sigmoid. Most of this
  ELLF is not associated with the erupting flux rope, but with a current
  shell that develops within expanding field lines above the rope. Only
  the short, curved end of the ELLF corresponds to a part of the flux
  rope. We argue that the features found in the simulation are generic
  for the formation and eruption of soft X-ray sigmoids.

---------------------------------------------------------
Title: Magnetic Flux Rope Eruption: Non Equilibrium versus Torus
    Instability
Authors: Demoulin, Pascal; Aulanier, Guillaume; Toeroek, Tibor;
   Deluca, Edward
2010cosp...38.1855D    Altcode: 2010cosp.meet.1855D
  The coronal magnetic configuration of an active region typically
  evolves quietly during few days before becoming suddenly eruptive
  and launching a CME. The precise origin of the eruption is still
  debated. Among other mechanisms, it has been long proposed that a
  loss of equilibrium, or an ideal MHD instability such as the torus
  instability, could be responsible for the sudden eruptivity. We first
  revisit both approaches with simple analytical models as well as with
  a 3D MHD simulation of an initially potential bipolar field, which
  evolves by means of simultaneous slow magnetic field diffusion and
  shearing motions in the photosphere. Reconnection of sheared arcade
  leads to the formation of a twisted flux rope, which corresponds to an
  electric current channel. We find that the electric current distribution
  and the field-line organization present in the MHD simulation provide
  an explanation for the recent X-rays Hinode observations of erupting
  sigmoidal regions. Next, we show analytically that the loss of
  equilibrium and the torus instability are two different views of the
  same physical mechanism. We compare the instability thresholds in the
  limit of straight and circular current channels, finding that they are
  closely comparable for thick current channels (as present in the MHD
  simulation and as expected in the corona) while these thresholds are
  well distinct at the limit of very thin current channels (as typically
  found in previous studies). Finally, including photospheric line tying
  of the current channel in the analytical models permits to have a
  closer comparison between instability thresholds found analytically
  and by the MHD simulation.

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Title: Ejective events from a complex active region
Authors: Mandrini, Cristina H.; Chandra, Ramesh; Pariat, Etienne;
   Schmieder, Brigitte; Demoulin, Pascal; Toeroek, Tibor; Uddin, Wahab
2010cosp...38.1886M    Altcode: 2010cosp.meet.1886M
  On 18 and 20 November 2003 active region (AR) 10501 produced a series of
  M flares all of them associated with coronal mass ejections (CMEs). The
  particularity of this AR is that while observational tracers of the
  magnetic helicity sign indicate that the large scale field in the
  region had a negative magnetic helicity sign, the MC associated
  to the most intense flare/CME on November 18 showed the opposite
  sign. Furthermore, the filaments observed on November 20 present
  morphological characteristics that correspond to a negative magnetic
  helicity sign, the rotation of the polarities of an emerging bipole
  indicate negative magnetic helicity sign injection; however, the flare
  ribbons observed after two homologous events can be connected either
  by field lines computed using a positive or a negative helicity sign
  magnetic field. We combine Hα, EUV, hard X-rays, and magnetic field
  data analysis with magnetic field modelling, and magnetic helicity
  injection computations to understand the origin of the helicity
  sign discrepancies discussed above. On November 20 magnetic field
  modeling and topology computations (in particular, the location of
  quasi-separatrix layers in relation to flare ribbons and evolution)
  give us clues about the CME initiation process.

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Title: Actors of the main activity of large complex centres during
    the 23 Solar Cycle maximum
Authors: Schmieder, Brigitte; Chandra, Ramesh; Demoulin, Pascal;
   Mandrini, Cristina H.; Venkatakrishnan, P.; Manoharan, P. K.; Uddin,
   Wahab; Pariat, Etienne; Toeroek, Tibor; Molodij, Guillaume; Kumar, P.
2010cosp...38.1861S    Altcode: 2010cosp.meet.1861S
  During the maximum of the last Solar Cycle solar cycle 23, large
  active regions had a long life spanning several solar rotations and
  produced a large number of X-ray class flares, CMEs and Magnetic
  clouds (MC). This was the case for the Halloween active regions in
  2003. The most geoeffective magnetic cloud of the cycle (Dst=-457)
  has its source in one passage of the active region (NOAA 10501) on
  November 18, 2003. Such an activity is presumably due to continuous
  emerging magnetic flux that was observed during this passage. Moreover,
  the region exhibited a complex topology with multiple domains of
  distinct magnetic helicities. The complexity is observed to reach
  such unprecedented levels that a detailed multi wavelength analysis
  is necessary to precisely identify the sources of CMEs and MCs.

---------------------------------------------------------
Title: Intensification of Plasma Upflows in an Active Region---Coronal
Hole Complex: A CME Precursor
Authors: Baker, D.; van Driel-Gesztelyi, L.; Murray, M. J.; Green,
   L. M.; Török, T.; Sun, J.
2009ASPC..415...75B    Altcode:
  We investigate the plasma flows resulting from the interaction between
  a mature active region (AR) and a surrounding equatorial coronal hole
  (CH) observed by Hinode's EIS and XRT from 15 to 18 October 2007. For 3
  days, EIS velocity maps showed upflows at the AR's eastern and western
  edges that were consistently between 5 and 10 km s<SUP>-1</SUP>, whereas
  downflows of up to 30 km s<SUP>-1</SUP> were seen in AR loops. However,
  on 18 October, velocity profiles of hotter coronal lines revealed
  intensification in upflow velocities of up to 18 km s<SUP>-1</SUP>
  at the AR's western footpoints 4.5 hours prior to a CME. We compare
  the AR's plasma flows with 2.5D MHD numerical simulations of the
  magnetic configuration, which show that expansion of the mature AR's
  loops drives upflows along the neighboring CH field. Further, the
  intensification of upflows observed on the AR's western side prior to
  a CME is interpreted to be the result of the expansion of a flux rope
  containing a filament further compressing the neighboring CH field.

---------------------------------------------------------
Title: Fan-Spine Topology Formation Through Two-Step Reconnection
    Driven by Twisted Flux Emergence
Authors: Török, T.; Aulanier, G.; Schmieder, B.; Reeves, K. K.;
   Golub, L.
2009ApJ...704..485T    Altcode: 2009arXiv0909.2235T
  We address the formation of three-dimensional nullpoint topologies
  in the solar corona by combining Hinode/X-ray Telescope (XRT)
  observations of a small dynamic limb event, which occurred beside
  a non-erupting prominence cavity, with a three-dimensional (3D)
  zero-β magnetohydrodynamics (MHD) simulation. To this end, we model
  the boundary-driven "kinematic" emergence of a compact, intense,
  and uniformly twisted flux tube into a potential field arcade that
  overlies a weakly twisted coronal flux rope. The expansion of the
  emerging flux in the corona gives rise to the formation of a nullpoint
  at the interface of the emerging and the pre-existing fields. We unveil
  a two-step reconnection process at the nullpoint that eventually yields
  the formation of a broad 3D fan-spine configuration above the emerging
  bipole. The first reconnection involves emerging fields and a set of
  large-scale arcade field lines. It results in the launch of a torsional
  MHD wave that propagates along the arcades, and in the formation of
  a sheared loop system on one side of the emerging flux. The second
  reconnection occurs between these newly formed loops and remote arcade
  fields, and yields the formation of a second loop system on the opposite
  side of the emerging flux. The two loop systems collectively display
  an anenome pattern that is located below the fan surface. The flux that
  surrounds the inner spine field line of the nullpoint retains a fraction
  of the emerged twist, while the remaining twist is evacuated along
  the reconnected arcades. The nature and timing of the features which
  occur in the simulation do qualititatively reproduce those observed
  by XRT in the particular event studied in this paper. Moreover, the
  two-step reconnection process suggests a new consistent and generic
  model for the formation of anemone regions in the solar corona.

---------------------------------------------------------
Title: 3D Reconstruction of an Erupting Prominence
Authors: Thompson, William T.; Kliem, B.; Toeroek, T.
2009SPD....40.2111T    Altcode:
  A bright prominence associated with a coronal mass ejection was seen
  erupting from the Sun on April 9, 2008. This prominence was tracked
  in both the STEREO EUVI and COR1 telescopes, and was seen to rotate or
  “swirl” as it erupted. Although the STEREO separation was 48 degrees,
  it was possible to match some sharp features in the later part of the
  eruption as seen in the 304 A line in EUVI by both STEREO Ahead and
  Behind. These features could then be traced out in three-dimensional
  space, and reprojected into a view in which the eruption is directed
  towards the observer. The reconstructed view shows that the alignment
  of the prominence rotates as it rises through the EUVI field-of-view
  out to 1.4 solar radii, and then remains constant as seen by COR1. The
  alignment at 1.4 solar radii differed by about 120 degrees from the
  original filament orientation. We will match the filament observations
  against a model of the event as kink instability in a flux rope.

---------------------------------------------------------
Title: Flux Emergence as a Trigger of Coronal Mass Ejections
Authors: Linton, Mark; Torok, T.
2009SPD....40.2202L    Altcode:
  We will present preliminary results from an investigation of Coronal
  Mass Ejections (CMEs) triggered by flux emergence. Related numerical
  simulations rely so far mostly on the kinematic, i.e. boundary-driven,
  emergence of magnetic flux at a photospheric boundary into the
  corona. We are investigating the viability of these models by studying
  the dynamical emergence of flux from a convection zone, through
  a temperature minimum photospheric region, into the corona. We are
  focusing on two CME models: the magnetic breakout model, and the ideal
  MHD torus instability model. Results from the breakout CME study will
  be shown at this meeting in the presentation by Leake et al. Here, we
  will show first results from the torus CME model. We build on recent
  simulations by Torok, where the torus instability of a pre-existing,
  stable coronal flux rope is triggered by kinematic flux emergence. We
  will report on our work to emerge flux dynamically in an equivalent
  configuration.

---------------------------------------------------------
Title: Solar prominences
Authors: Schmieder, Brigitte; Aulanier, Guillaume; Török, Tibor
2009IAUS..257..223S    Altcode:
  Solar filaments (or prominences) are magnetic structures in the
  corona. They can be represented by twisted flux ropes in a bipolar
  magnetic environment. In such models, the dipped field lines of the
  flux rope carry the filament material and parasitic polarities in the
  filament channel are responsible for the existence of the lateral feet
  of prominences. <P />Very simple laws do exist for the chirality of
  filaments, the so-called “filament chirality rules”: commonly
  dextral/sinistral filaments corresponding to left- (resp. right)
  hand magnetic twists are in the North/South hemisphere. Combining
  these rules with 3D weakly twisted flux tube models, the sign of the
  magnetic helicity in several filaments were identified. These rules
  were also applied to the 180° disambiguation of the direction of the
  photospheric transverse magnetic field around filaments using THEMIS
  vector magnetograph data (López Ariste et al. 2006). Consequently,
  an unprecedented evidence of horizontal magnetic support in filament
  feet has been observed, as predicted by former magnetostatic and
  recent MHD models. <P />The second part of this review concerns the
  role of emerging flux in the vicinity of filament channels. It has been
  suggested that magnetic reconnection between the emerging flux and the
  pre-existing coronal field can trigger filament eruptions and CMEs. For
  a particular event, observed with Hinode/XRT, we observe signatures of
  such a reconnection, but no eruption of the filament. We present a 3D
  numerical simulation of emerging flux in the vicinity of a flux rope
  which was performed to reproduce this event and we briefly discuss,
  based on the simulation results, why the filament did not erupt.

---------------------------------------------------------
Title: Eruption of magnetic flux ropes during flux emergence
Authors: Archontis, V.; Török, T.
2008A&A...492L..35A    Altcode: 2008arXiv0811.1134A
  Aims: We investigate the formation of flux ropes in a flux
  emergence region and their rise into the outer atmosphere of the
  Sun. <BR />Methods: We perform 3D numerical experiments by solving
  the time-dependent and resistive MHD equations. <BR />Results: A
  sub-photospheric twisted flux tube rises from the solar interior
  and expands into the corona. A flux rope is formed within the
  expanding field, due to shearing and reconnection of field lines at
  low atmospheric heights. If the tube emerges into a non-magnetized
  atmosphere, the flux rope rises, but remains confined inside the
  expanding magnetized volume. In contrast, if the expanding tube is
  allowed to reconnect with a pre-existing coronal field, the flux rope
  experiences a full eruption with a rise profile that is in qualitative
  agreement with erupting filaments and Coronal Mass Ejections.

---------------------------------------------------------
Title: Simulations of the CME-Flare Relationship
Authors: Kliem, B.; Török, T.; Forbes, T. G.
2008AGUFMSH23B1648K    Altcode:
  Observations of coronal mass ejections (CMEs) and solar flares have
  revealed a high correlation between the acceleration of the ejecta
  and the plasma heating and particle acceleration signified by the
  soft and hard X-ray emissions of the associated flare. The latter are
  generally thought to result from magnetic reconnection. This finding
  has stimulated the discussion of the CME-flare relationship, but at
  the same time it has made it difficult to find a conclusive answer as
  to whether magnetic reconnection or an ideal MHD instability is the
  prime cause of the eruptions. Numerical simulations of unstable flux
  ropes will be presented that are in very satisfactory quantitative
  agreement with erupting filaments, both, confined to the corona and
  ejective (i.e., developing into a CME). Some of these simulations
  indeed show a high degree of synchronization between the initial
  exponential acceleration of the flux rope, due to the ideal MHD
  instability, and the development of reconnection flows. However,
  others show a very delayed onset of reconnection, even after the
  flux rope's acceleration peak. In addition, the reconnection flows
  generally lag behind the motions driven by the ideal instability as
  the flux rope rise velocity nears the saturation phase. Comparison of
  the simulation results with observations suggests that the ideal MHD
  process is the primary driver of the coupled CME-flare phenomenon. The
  strong differences in the degree of synchronization, which the simulated
  systems show in the main rise phase of the eruption, are related to
  the magnetic topology prior to the eruption. Given the observational
  result of a high correlation between CME and flare development (Zhang
  &amp; Dere 2006), these simulations yield constraints on the topology
  and lead us to conclude that a seed for a reconnecting current sheet
  must typically be present already at the onset of the eruption.

---------------------------------------------------------
Title: Magnetofrictional Extrapolations of Current-Carrying Flux Ropes
Authors: Valori, G.; Kliem, B.; Toeroek, T.
2008ESPM...12.2.90V    Altcode:
  The quiescent solar corona is regularly modified by very fast ejections
  of coronal material and magnetic field (CME) that occur preferably
  above active regions. Most CME models require the formation of twisted
  magnetic field structures (flux ropes) before or during such events. <P
  />Unfortunately, the coronal magnetic field is not directly measurable
  at present, and therefore it is difficult to verify the validity
  of different CME models. <P />In order to remove this obstacle, the
  extrapolation of photospheric magnetic field measurements can be used
  to reconstruct the missing coronal information. As an application of
  our magneto-frictional code, we present an extrapolation of a measured
  magnetogram where a flux rope is found. <P />In such applications it
  is necessary to estimate how well our extrapolation code can reproduce
  all aspects of highly nonlinear structures such as flux ropes. This is
  of course possible only using test fields. <P />The Titov and Demoulin
  force-free equilibrium (Titov and Demoulin, Astr. and Astrophys. 351,
  707, (1999), hereafter TD) models a semi-circular, 3D current-carrying
  flux rope by means of a current ring embedded in a potential field. The
  parameters of the TD model can be adjusted to create both stable and
  kink- and torus-unstable configurations. <P />Its solar relevance
  was confirmed by the quantitative reproduction of some specific CME
  features (see e.g., Toeroek and Kliem, Astroph. J. Lett. 630 L97
  (2005)). <P />Therefore, the TD solution is by far the most realistic
  analytical equilibrium available to date for the modeling of solar
  active regions. <P />Employing the TD equilibrium as a test-field,
  we show that the magnetofrictional extrapolation code can reproduce
  the energy and the twist of the magnetic field within a percent
  accuracy. <P />This information is essential for the reconstruction
  of coronal fields involved in eruptions because the twist is,
  together with the height profile of the overlying potential field,
  the most important stability parameter -- at least as long as the
  TD equilibrium is a good model of the considered active region. <P
  />Perfectly reproduced are also X-type magnetic topology features,
  sometimes referred to as Hyperbolic Flux Tubes, which are regarded to be
  essential to the physics of CMEs and flares because they are preferred
  locations for the formation of current sheets. <P />On the other hand,
  we also show how the scale-height of the potential field that is used
  as initial condition in the extrapolation influences the quality of the
  reconstructed field: different initial conditions reproduce correctly
  the twist and the topology, but less accurately the height and the
  shape of the flux rope. <P />Consequently, care must be taken when
  comparing the shapes of soft X-ray and EUV loops, especially those in
  the nearly potential field overlying filaments, with the field lines
  obtained from the extrapolation of the corresponding magnetogram.

---------------------------------------------------------
Title: Modelling CMEs close to the Sun
Authors: Török, T.
2008ESPM...12.3.32T    Altcode:
  It is now widely accepted that large-scale solar eruptive phenomena like
  flares, eruptive prominences or filaments, and coronal mass ejections
  (CMEs) are magnetically driven. They are different observational
  manifestations of a more general process, namely a large-scale
  disruption of the coronal magnetic field ("solar eruption" in the
  following). It is also widely accepted that the energy necessary to
  drive solar eruptions is stored in the low corona, in form of sheared
  and twisted magnetic fields which are held in equilibrium prior to
  eruption by the ambient coronal field. An eruption occurs if this
  equilibrium is driven or perturbed such that it becomes unstable. In
  spite of this general understanding, the detailed processes which
  initiate and drive solar eruptions are not yet well understood. Several
  mechanisms have been proposed in the last decades. In recent years, the
  availability of 3D MHD simulations has helped to test the models and has
  greatly increased our understanding of these processes. In this talk,
  I will review current theoretical models and corresponding numerical
  simulations of solar eruptions. I will outline their differences and
  similarities and briefly discuss how current and future observations
  can help us to constrain the models. The simulation results indicate
  a flux rope instability or loss of equilibrium to be the canonical
  driving mechanism of solar eruptions in their fast acceleration phase
  close to the Sun, and they point towards a relatively large variety
  of possible mechanisms that initiate that phase. As an example for
  such an initiation mechanism, I will present new simulations which
  show how the eruption of a pre-existing 3D coronal flux rope can be
  triggered by magnetic flux emergence.

---------------------------------------------------------
Title: Simulations of the CME-Flare Relationship
Authors: Kliem, B.; Török, T.
2008ESPM...12.3.67K    Altcode:
  Observations of coronal mass ejections (CMEs) and solar flares have
  revealed a high correlation between the acceleration of the ejecta
  and the plasma heating and particle acceleration signified by the
  soft and hard X-ray emissions of the associated flare. The latter are
  generally thought to result from magnetic reconnection. This finding has
  stimulated the discussion of the CME-flare relationship, but at the same
  time it has made it difficult to find a conclusive answer as to whether
  magnetic reconnection or an ideal MHD instability is the prime cause of
  the eruptions. <P />Numerical simulations of unstable flux ropes will
  be presented that are in very satisfactory quantitative agreement with
  erupting filaments, both, confined to the corona and ejective (i.e.,
  developing into a CME). Some of these simulations indeed show a high
  degree of synchronization between the initial exponential acceleration
  of the flux rope, due to the ideal MHD instability, and the development
  of reconnection flows. However, others show a very delayed onset of
  reconnection, even after the flux rope's acceleration peak. In addition,
  the reconnection flows generally lag behind the motions driven by the
  ideal instability as the flux rope rise velocity nears the saturation
  phase. Both findings indicate that the ideal MHD process is the primary
  driver of the coupled CME-flare phenomenon. <P />The strong differences
  in the degree of synchronization, which the simulated systems show
  in the main rise phase of the eruption, are related to the magnetic
  topology prior to the eruption. Given the observational result of
  a high correlation between CME and flare development (Zhang &amp;
  Dere 2006), these simulations yield constraints on the topology and
  lead us to conclude that a seed for a reconnecting current sheet must
  typically be present already at the onset of the eruption.

---------------------------------------------------------
Title: Magnetic field changes preceding filament eruptions and
    coronal mass ejections
Authors: Schmieder, B.; Török, T.; Aulanier, G.
2008AIPC.1043..260S    Altcode:
  Solar filaments (or prominences) can be represented by twisted flux
  ropes in a bipolar magnetic environment. In such models, the dipped
  field lines of the flux rope carry the filament material and parasitic
  polarities in the filament channel are responsible for the existence
  of the lateral feet of filaments. Most filaments eventually erupt, in
  many cases as part of a coronal mass ejection (CME). Such eruptions are
  often preceded by detectable changes in the photospheric magnetic field
  in the vicinity of the filament. We first review recent observations of
  such changes due to large-scale flows or variations of the background
  magnetic field, and we discuss their role in eruptions. We then focus
  on emerging flux in the vicinity of filament channels. It has been
  suggested that magnetic reconnection between the emerging flux and
  the pre-existing coronal field can trigger filament eruptions and
  CMEs. For a particular event, observed with Hinode/XRT, we observe
  signatures of such reconnection, but no eruption of the filament. We
  present a numerical simulation of this event and we briefly argue why
  no eruption took place in this case.

---------------------------------------------------------
Title: Twist, Writhe and Rotation of Magnetic Flux Ropes in Filament
    Eruptions and Coronal Mass Ejections
Authors: Török, T.; Berger, M. A.; Kliem, B.; Démoulin, P.; Linton,
   M.; van Driel-Gesztelyi, L.
2008ESPM...12.3.54T    Altcode:
  We present the first quantitative analysis of the conversion of twist
  into writhe in the course of ideal MHD instabilities in erupting coronal
  magnetic flux ropes. For our analysis, we consider numerical simulations
  of two instabilities which have been suggested as trigger and initial
  driving mechanisms in filament eruptions and coronal mass ejections,
  namely the helical kink instability and the torus instability. We
  use two different coronal flux rope models as initial conditions
  in the simulations, namely the cylindrical Gold-Hoyle equilibrium
  and the toroidal Titov-Demoulin equilibrium. <P />For each model, we
  perform a series of simulations with different amounts of initial flux
  rope twist. In order to study both confined and ejective eruptions,
  we additionally use different initial potential fields overlying
  the flux rope in the simulations of the Titov-Demoulin model. <P
  />In all simulations, we measure the writhe of the flux rope and the
  corresponding rotation of its axis in vertical projection by making use
  of recently developed expressions which permit us to calculate writhe as
  a single integral in space. We discuss the implications of our results
  for filament eruptions, coronal mass ejections and magnetic clouds.

---------------------------------------------------------
Title: Observations and Modeling of the Early Acceleration Phase of
    Erupting Filaments Involved in Coronal Mass Ejections
Authors: Schrijver, Carolus J.; Elmore, Christopher; Kliem, Bernhard;
   Török, Tibor; Title, Alan M.
2008ApJ...674..586S    Altcode: 2007arXiv0710.1609S
  We examine the early phases of two near-limb filament destabilizations
  involved in coronal mass ejections (CMEs) on 2005 June 16 and July
  27, using high-resolution, high-cadence observations made with the
  Transition Region and Coronal Explorer (TRACE), complemented by
  coronagraphic observations by the Mauna Loa Solar Observatory (MLSO)
  and the Solar and Heliospheric Observatory (SOHO). The filaments'
  heights above the solar limb in their rapid-acceleration phases are
  best characterized by a height dependence h(t) propto t<SUP>m</SUP>
  with m near, or slightly above, 3 for both events. Such profiles are
  incompatible with published results for breakout, MHD-instability,
  and catastrophe models. We show numerical simulations of the
  torus instability that approximate this height evolution in case a
  substantial initial velocity perturbation is applied to the developing
  instability. We argue that the sensitivity of magnetic instabilities
  to initial and boundary conditions requires higher fidelity modeling of
  all proposed mechanisms if observations of rise profiles are to be used
  to differentiate between them. The observations show no significant
  delays between the motions of the filament and of overlying loops:
  the filaments seem to move as part of the overall coronal field until
  several minutes after the onset of the rapid-acceleration phase.

---------------------------------------------------------
Title: Interaction between emerging flux and coronal hole -
    observations and simulations
Authors: van Driel-Gesztelyi, Lidia; Baker, Deborah; Murray, Michelle;
   Demoulin, Pascal; Attrill, Gemma; Matthews, Sarah A.; Mandrini,
   Cristina H.; Toeroek, Tibor
2008cosp...37.3288V    Altcode: 2008cosp.meet.3288V
  Flux emergence in the vicinity of or inside a coronal hole (CH) is
  expected to induce magnetic reconnection between the closed emerging
  and open CH magnetic field lines, resulting in an evolution of the
  CH as formerly closed field lines become topologically open, while at
  the same time, open field lines close down. Through two case studies
  we show observational signatures of this (interchange) reconnection
  process and discuss its implications. First, using SOHO EIT and MDI
  data, we study a small active region (AR10869) emerging in the close
  vicinity of a low-latitude coronal hole in April 2006. The interfacing
  magnetic polarities between the AR and the CH were opposite, favourable
  for magnetic reconnection. We indeed observe the coupled formation of
  bright closed loops between the CH and the AR and coronal dimming on
  the far side of the AR, which we interpret as evidence of interchange
  reconnection. This process effectively modifies the CH boundary
  (making it retreat), while simultaneously displacing open field lines
  to the far side of the AR. In order to study this process in detail,
  we perform 2.5D MHD simulations, which qualitatively reproduce important
  aspects of the observations. We expect to find upflows of plasma at the
  location where previously closed field lines are opening up as well as
  on the reconnecting side, but since we had no spectroscopic data for
  this event, we can not verify this. Therefore we analyze Hinode/EIS
  line-of-sight velocity maps of another low-latitude CH with a small AR
  in its midst observed on 18 Oct. 2007. We find that while closed loops
  of the bipole are dominated by downflows in the Fe XII, Fe XIII and
  Fe XV lines, the strongest coronal plasma upflows are indeed located
  around and particularly at the "far side" of the bipolar AR, i.e. having
  the same polarity as the dominant polarity of the CH. The emerging
  biplole and the series of interchange reconnections it induces create
  a significant additional plasma upflow in the CH, thus we identify
  this outflow must contribute to the acceleration of the fast solar wind.

---------------------------------------------------------
Title: Numerical modelling of solar eruptions
Authors: Toeroek, Tibor
2008cosp...37.3194T    Altcode: 2008cosp.meet.3194T
  It is now widely accepted that large-scale solar eruptive phenomena like
  flares, eruptive prominences or filaments, and coronal mass ejections
  (CMEs) are magnetically driven. They are different observational
  manifestations of a more general process, namely a large-scale
  disruption of the coronal magnetic field ("solar eruption" in the
  following). It is also widely accepted that the energy necessary to
  drive solar eruptions is stored in the low corona, in form of sheared
  and twisted magnetic fields which are held in equilibrium prior to
  eruption by the ambient coronal field. An eruption occurs if this
  equilibrium is driven or perturbed such that it becomes unstable. In
  spite of this general understanding, the detailed processes which
  initiate and drive solar eruptions are not yet well understood. Several
  mechanisms have been proposed in the last decades. In recent years, the
  availability of 3D MHD simulations has helped to test the models and has
  greatly increased our understanding of these processes. In this talk,
  I will review the main theoretical models and corresponding numerical
  simulations of solar eruptions. I will outline their differences and
  similarities and briefly discuss how current and future observations
  can help us to constrain the models. The simulation results indicate a
  flux rope instability or loss of equilibrium to be the canonical driving
  mechanism of solar eruptions in their fast acceleration phase, and they
  point towards a relatively large variety of possible mechanisms that
  initiate that phase. These initiation mechanisms are strongly related
  to the coupling between the photosphere and the corona. As an example,
  I will present new simulations which show for the first time how the
  eruption of a pre-existing 3D coronal flux rope can be triggered by
  magnetic flux emergence.

---------------------------------------------------------
Title: What kinking filament eruptions tell us about the physical
    nature of transient coronal sigmoids ?
Authors: van Driel-Gesztelyi, Lidia; Green, Lucie M.; Kliem, Bernhard;
   Toeroek, Tibor; Attrill, Gemma
2008cosp...37.3289V    Altcode: 2008cosp.meet.3289V
  Soft X-ray images of the Sun have shown that some active regions contain
  loops, or collections of loops, which appear forward or reverse 'S'
  in shape. These features have been termed sigmoids. These structures
  are of interest because their presence in an active region has been
  linked to eruptive activity and the sense of sigmoid orientation is
  taken to indicate the sense of shear and twist (or helicity) in the
  magnetic field. Differing models have been put forward in order to
  explain the physical nature of sigmoids and the role they play in an
  eruption. We use multiwavelength observations (Yohkoh/SXT, TRACE,
  SOHO/EIT and MDI, H-alpha) to investigate how transient sigmoids
  are formed. We also investigate filament eruptions from these active
  regions, which show a clear sign of rotation of their apex. We find
  that for positive (negative) helicity the filament apex rotates
  clockwise (counterclockwise), consistent with the flux rope taking on
  a reverse (forward) S shape, which is opposite to that observed for
  the sigmoid. These observations put constraints on sigmoid models,
  excluding some of them. We conclude that transient sigmoids are
  associated with the formation of current sheets and heating along
  field lines under a dynamic flux rope.

---------------------------------------------------------
Title: A New Model for Propagating Parts of EIT Waves: A Current
    Shell in a CME
Authors: Delannée, C.; Török, T.; Aulanier, G.; Hochedez, J. -F.
2008SoPh..247..123D    Altcode:
  EIT waves are observed in EUV as bright fronts. Some of these bright
  fronts propagate across the solar disk. EIT waves are all associated
  with a flare and a CME and are commonly interpreted as fast-mode
  magnetosonic waves. Propagating EIT waves could also be the direct
  signature of the gradual opening of magnetic field lines during a
  CME. We quantitatively addressed this alternative interpretation. Using
  two independent 3D MHD codes, we performed nondimensional numerical
  simulations of a slowly rotating magnetic bipole, which progressively
  result in the formation of a twisted magnetic flux tube and its fast
  expansion, as during a CME. We analyse the origins, the development,
  and the observability in EUV of the narrow electric currents sheets that
  appear in the simulations. Both codes give similar results, which we
  confront with two well-known SOHO/EIT observations of propagating EIT
  waves (7 April and 12 May 1997), by scaling the vertical magnetic field
  components of the simulated bipole to the line of sight magnetic field
  observed by SOHO/MDI and the sign of helicity to the orientation of the
  soft X-ray sigmoids observed by Yohkoh/SXT. A large-scale and narrow
  current shell appears around the twisted flux tube in the dynamic phase
  of its expansion. This current shell is formed by the return currents
  of the system, which separate the twisted flux tube from the surrounding
  fields. It intensifies as the flux tube accelerates and it is co-spatial
  with weak plasma compression. The current density integrated over the
  altitude has the shape of an ellipse, which expands and rotates when
  viewed from above, reproducing the generic properties of propagating
  EIT waves. The timing, orientation, and location of bright and faint
  patches observed in the two EIT waves are remarkably well reproduced. We
  conjecture that propagating EIT waves are the observational signature of
  Joule heating in electric current shells, which separate expanding flux
  tubes from their surrounding fields during CMEs or plasma compression
  inside this current shell. We also conjecture that the bright edges
  of halo CMEs show the plasma compression in these current shells.

---------------------------------------------------------
Title: Transient Coronal Sigmoids and Rotating Erupting Flux Ropes
Authors: Green, L. M.; Kliem, B.; Török, T.; van Driel-Gesztelyi,
   L.; Attrill, G. D. R.
2007SoPh..246..365G    Altcode:
  To determine the relationship between transient coronal (soft X-ray
  or EUV) sigmoids and erupting flux ropes, we analyse four events
  in which a transient sigmoid could be associated with a filament
  whose apex rotates upon eruption and two further events in which
  the two phenomena were spatially but not temporally coincident. We
  find the helicity sign of the erupting field and the direction of
  filament rotation to be consistent with the conversion of twist
  into writhe under the ideal MHD constraint of helicity conservation,
  thus supporting our assumption of flux rope topology for the rising
  filament. For positive (negative) helicity the filament apex rotates
  clockwise (counterclockwise), consistent with the flux rope taking on
  a reverse (forward) S shape, which is opposite to that observed for
  the sigmoid. This result is incompatible with two models for sigmoid
  formation: one identifying sigmoids with upward arching kink-unstable
  flux ropes and one identifying sigmoids with a current layer between
  two oppositely sheared arcades. We find instead that the observations
  agree well with the model by Titov and Démoulin (Astron. Astrophys.351,
  707, 1999), which identifies transient sigmoids with steepened current
  layers below rising flux ropes.

---------------------------------------------------------
Title: Numerical simulations of fast and slow coronal mass ejections
Authors: Török, T.; Kliem, B.
2007AN....328..743T    Altcode: 2007arXiv0705.2100T
  Solar coronal mass ejections (CMEs) show a large variety in their
  kinematic properties. CMEs originating in active regions and accompanied
  by strong flares are usually faster and accelerated more impulsively
  than CMEs associated with filament eruptions outside active regions
  and weak flares. It has been proposed more than two decades ago that
  there are two separate types of CMEs, fast (impulsive) CMEs and slow
  (gradual) CMEs. However, this concept may not be valid, since the large
  data sets acquired in recent years do not show two distinct peaks
  in the CME velocity distribution and reveal that both fast and slow
  CMEs can be accompanied by both weak and strong flares. We present
  numerical simulations which confirm our earlier analytical result
  that a flux-rope CME model permits describing fast and slow CMEs in
  a unified manner. We consider a force-free coronal magnetic flux rope
  embedded in the potential field of model bipolar and quadrupolar active
  regions. The eruption is driven by the torus instability which occurs
  if the field overlying the flux rope decreases sufficiently rapidly
  with height. The acceleration profile depends on the steepness of
  this field decrease, corresponding to fast CMEs for rapid decrease,
  as is typical of active regions, and to slow CMEs for gentle decrease,
  as is typical of the quiet Sun. Complex (quadrupolar) active regions
  lead to the fastest CMEs.

---------------------------------------------------------
Title: The Evolving Sigmoid: Evidence for Magnetic Flux Ropes in
    the Corona Before, During, and after CMES
Authors: Gibson, S. E.; Fan, Y.; Török, T.; Kliem, B.
2007sdeh.book..131G    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The Evolving Sigmoid: Evidence for Magnetic Flux Ropes in
    the Corona Before, During, and After CMES
Authors: Gibson, S. E.; Fan, Y.; Török, T.; Kliem, B.
2006SSRv..124..131G    Altcode: 2007SSRv..tmp...52G
  It is generally accepted that the energy that drives coronal mass
  ejections (CMEs) is magnetic in origin. Sheared and twisted coronal
  fields can store free magnetic energy which ultimately is released
  in the CME. We explore the possibility of the specific magnetic
  configuration of a magnetic flux rope of field lines that twist
  about an axial field line. The flux rope model predicts coronal
  observables, including heating along forward or inverse S-shaped,
  or sigmoid, topological surfaces. Therefore, studying the observed
  evolution of such sigmoids prior to, during, and after the CME gives
  us crucial insight into the physics of coronal storage and release of
  magnetic energy. In particular, we consider (1) soft-X-ray sigmoids,
  both transient and persistent; (2) The formation of a current sheet
  and cusp-shaped post-flare loops below the CME; (3) Reappearance of
  sigmoids after CMEs; (4) Partially erupting filaments; (5) Magnetic
  cloud observations of filament material.

---------------------------------------------------------
Title: Flux Ropes and CMEs: The Kink and Torus Instabilities,
    Catastrophe, and Magnetic Reconnection
Authors: Kliem, Bernhard; Toeroek, T.
2006SPD....37.0820K    Altcode: 2006BAAS...38..234K
  Prior to eruption, the coronal magnetic field evolves along an
  equilibrium sequence due to slow photospheric changes. Configurations
  containing a flux rope can erupt when the rope passes the threshold
  of an instability in the sequence or when the rope is driven beyond
  an end point of the sequence in parameter space (catastrophe). The
  kink instability of a flux rope yields quantitative agreement with
  characteristic properties of many CMEs during their onset and early
  evolution: development of helical shape and exponential-to-linear rise
  profiles. The large-scale evolution of kinking flux ropes is governed
  by the torus (expansion) instability (TI). This instability yields a
  unified description of fast and slow CMEs, the preferred occurrence of
  very fast CMEs in quadrupolar active regions, and an indication why
  the minor flux rope radius expands overproportionally in the course
  of the eruption, creating or deepening the cavity seen in three-part
  CMEs. If an eruption is triggered by a flux rope catastrophe, we expect
  its evolution to possess characteristics similar to the TI-driven
  case. The magnetic reconnection that commences in the wake of a rising
  unstable flux rope is an integral part of the eruption and proceeds
  in a highly dynamic and complex manner, forming many intermittent X-
  and O-type structures along a vertical current sheet.

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Title: Torus Instability
Authors: Kliem, B.; Török, T.
2006PhRvL..96y5002K    Altcode: 2006physics...5217K
  The expansion instability of a toroidal current ring in low-beta
  magnetized plasma is investigated. Qualitative agreement is obtained
  with experiments on spheromak expansion and with essential properties
  of solar coronal mass ejections, unifying the two apparently disparate
  classes of fast and slow coronal mass ejections.

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Title: Confined and Ejective Eruptions of Kink-unstable Flux Ropes
Authors: Török, T.; Kliem, B.
2005ApJ...630L..97T    Altcode: 2005astro.ph..7662T
  The ideal helical kink instability of a force-free coronal magnetic
  flux rope, anchored in the photosphere, is studied as a model for
  solar eruptions. Using the flux rope model of Titov and Démoulin
  as the initial condition in MHD simulations, both the development of
  helical shape and the rise profile of a confined (or failed) filament
  eruption (on 2002 May 27) are reproduced in very good agreement
  with the observations. By modifying the model such that the magnetic
  field decreases more rapidly with height above the flux rope, a full
  (or ejective) eruption of the rope is obtained in very good agreement
  with the developing helical shape and the exponential-to-linear rise
  profile of a fast coronal mass ejection (CME) on 2001 May 15. This
  confirms that the helical kink instability of a twisted magnetic flux
  rope can be the mechanism of the initiation and the initial driver
  of solar eruptions. The agreement of the simulations with properties
  that are characteristic of many eruptions suggests that they are often
  triggered by the kink instability. The decrease of the overlying field
  with height is a main factor in deciding whether the instability leads
  to a confined event or to a CME.

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Title: Eruption of a Kink-unstable Filament in NOAA Active Region
    10696
Authors: Williams, David R.; Török, Tibor; Démoulin, Pascal;
   van Driel-Gesztelyi, Lidia; Kliem, Bernhard
2005ApJ...628L.163W    Altcode: 2005astro.ph..7661W
  We present rapid-cadence Transition Region and Coronal Explorer (TRACE)
  observations that show evidence of a filament eruption from NOAA active
  region 10696, accompanied by an X2.5 flare, on 2004 November 10. The
  eruptive filament, which manifests as a fast coronal mass ejection
  some minutes later, rises as a kinking structure with an apparently
  exponential growth of height within TRACE's field of view. We compare
  the characteristics of this filament eruption with MHD numerical
  simulations of a kink-unstable magnetic flux rope, finding excellent
  qualitative agreement. We suggest that while tether weakening by
  breakout-like quadrupolar reconnection may be the release mechanism
  for the previously confined flux rope, the driver of the expansion is
  most likely the MHD helical kink instability.

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Title: The Kink Instability in Solar Eruptions
Authors: Török, T.; Kliem, B.
2004ESASP.575...56T    Altcode: 2004soho...15...56T
  No abstract at ADS

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Title: The kink instability of a coronal magnetic loop as a trigger
    mechanism for solar eruptions
Authors: Török, T.; Kliem, B.
2004PADEU..14..165T    Altcode:
  The kink instability of twisted magnetic flux tubes in the solar corona
  is regarded as a possible initiation process of solar eruptions. We
  study the stability properties and the dynamic evolution of such
  coronal magnetic loops using 3D numerical simulations within the
  framework of ideal MHD. The analytical force-free coronal loop
  model by Titov and Demoulin (1999) is used as initial condition in
  the simulations. The loop model is found to be kink-unstable if a
  critical twist is exceeded. The growing kink perturbation leads to the
  formation of current sheets, which steepen exponentially and define
  the locations of plasma heating. Due to the twist in the magnetic
  field, the heated structures are S shaped - in very good agreement
  with soft X-ray observations of solar eruptions. The model, however,
  does not yet show a successful eruption, rather the kink instability
  starts to saturate. We present an improvement of the model which is
  promising with regard to eruption: a modification of the equilibrium
  so that the magnetic field surrounding the loop decreases more rapidly
  with height above the photosphere. Furthermore, we briefly discuss
  how the simulation results can be related to observations of solar
  eruptive phenomena.

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Title: Ideal kink instability of a magnetic loop equilibrium
Authors: Török, T.; Kliem, B.; Titov, V. S.
2004A&A...413L..27T    Altcode: 2003astro.ph.11198T
  The force-free coronal loop model by \cite{Tit:Dem-99} is found
  to be unstable with respect to the ideal kink mode, which suggests
  this instability as a mechanism for the initiation of flares. The
  long-wavelength (m = 1) mode grows for average twists Φ⪆3.5π (at a
  loop aspect ratio of ≈5). The threshold of instability increases with
  increasing major loop radius, primarily because the aspect ratio then
  also increases. Numerically obtained equilibria at subcritical twist
  are very close to the approximate analytical equilibrium; they do not
  show indications of sigmoidal shape. The growth of kink perturbations
  is eventually slowed down by the surrounding potential field, which
  varies only slowly with radius in the model. With this field a global
  eruption is not obtained in the ideal MHD limit. Kink perturbations with
  a rising loop apex lead to the formation of a vertical current sheet
  below the apex, which does not occur in the cylindrical approximation.

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Title: Formation of current sheets and sigmoidal structure by the
    kink instability of a magnetic loop
Authors: Kliem, B.; Titov, V. S.; Török, T.
2004A&A...413L..23K    Altcode: 2003astro.ph.11199K
  We study dynamical consequences of the kink instability of a
  twisted coronal flux rope, using the force-free coronal loop
  model by \cite{Tit:Dem-99} 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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Title: The kink instability of a coronal magnetic loop as a trigger
    mechanism for solar eruptions
Authors: Török, T.; Kliem, B.; Titov, V. S.
2004cosp...35.3327T    Altcode: 2004cosp.meet.3327T
  MHD instabilities of twisted magnetic flux tubes in the solar corona
  are regarded as a possible initiation process of solar eruptions. We
  study the stability properties and the dynamic evolution of coronal
  magnetic loops using 3D numerical simulations within the framework of
  ideal MHD. The analytical force-free coronal loop model by Titov and
  Démoulin (1999) is used as initial condition in the simulations. The
  loop model is found to be kink-unstable if a critical twist is
  exceeded. The growing kink perturbation leads to the formation of
  current sheets, which steepen exponentially and define the locations
  of plasma heating. Due to the twist in the magnetic field, the heated
  structures are S shaped -- in very good agreement with sigmoidal soft
  X-ray structures that brighten in solar eruptions. The model, however,
  does not yet show a successful eruption, rather the kink instability
  starts to saturate. We present an improvement of the model which is
  promising with regard to eruption: a modification of the equilibrium so
  that the magnetic field surrounding the loop decreases more rapidly with
  height above the photosphere. Furthermore, we discuss how the simulation
  results can be related to observations of solar eruptive phenomena.

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Title: Instabilität magnetischer Flußröhren in solaren Eruptionen

---------------------------------------------------------
Title: Instabilität magnetischer Flußröhren in solaren Eruptionen
Authors: Török, Tibor
2004PhDT.......150T    Altcode:
  No abstract at ADS

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Title: The evolution of twisting coronal magnetic flux tubes
Authors: Török, T.; Kliem, B.
2003A&A...406.1043T    Altcode:
  We simulate the twisting of an initially potential coronal flux
  tube by photospheric vortex motions, centred at two photospheric
  flux concentrations, using the compressible zero-beta ideal MHD
  equations. A twisted flux tube is formed, surrounded by much less
  twisted and sheared outer flux. Under the action of continuous slow
  driving, the flux tube starts to evolve quasi-statically along a
  sequence of force-free equilibria, which rise slowly with increasing
  twist and possess helical shape. The flux bundle that extends from
  the location of peak photospheric current density (slightly displaced
  from the vortex centre) shows a sigmoidal shape in agreement with
  observations of sigmoidal soft X-ray loops. There exists a critical
  twist, above which no equilibrium can be found in the simulation
  and the flux tube ascends rapidly. Then either stable equilibrium
  ceases to exist or the character of the sequence changes such that
  neighbouring stable equilibria rise by enormous amounts for only modest
  additions of twist. A comparison with the scalings of the rise of flux
  in axisymmetric geometry by \cite{Stur:al-95} suggests the former. Both
  cases would be observed as an eruption. The critical end-to-end twist,
  for a particular set of parameters describing the initial potential
  field, is found to lie in the range 2.5pi &lt;Phi<SUB>c</SUB>&lt;2.75pi
  . There are some indications for the growth of helical perturbations
  at supercritical twist. Depending on the radial profiles of the
  photospheric flux concentration and vortex velocity, the outer part
  or all of the twisted flux expands from the central field line of the
  flux tube. This effect is particularly efficient in the dynamic phase,
  provided the density is modeled realistically, falling off sufficiently
  rapidly with height. It is expected to lead to the formation of a
  cavity in which the twisted flux tube is embedded, analogous to the
  typical structure of coronal mass ejections.

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Title: Formation of Current Sheets and Sigmoidal Structure by the
    Ideal Kink Instability of a Magnetic Loop
Authors: Kliem, Bernhard; Török, Tibor; Titov, Viatcheslav S.
2003ANS...324...73K    Altcode: 2003ANS...324..I16K
  No abstract at ADS

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Title: The evolution of coronal magnetic flux tubes twisted by
    photospheric vortex motions
Authors: Török, T.; Kliem, B.
2002ESASP.506..781T    Altcode: 2002svco.conf..781T; 2002ESPM...10..781T
  We simulate the twisting of initially potential coronal magnetic
  flux by slow photospheric vortex motions using the compressional,
  zero-beta ideal MHD equations. The twisted flux tube starts to
  evolve quasi-statically along a sequence of force-free equilibria,
  rising slowly and possessing helical shape. As a critical amount of
  twist is reached, the evolution becomes dynamic and the tube rises
  and expands rapidly. No neighbouring equilibrium can be found in the
  simulation domain at this stage of the evolution, as confirmed by
  relaxation runs. Hence, above the critical twist either the flux tube
  becomes unstable or neighbouring equilibria rise by enormous amounts
  for only small additional twist. Both cases would be observed as an
  eruption. The critical end-to-end twist of the flux tube is found to
  lie in the range 2.5π &lt; Φ<SUB>c</SUB> &lt; 3.0π.

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Title: The evolution of coronal magnetic flux tubes subject to
    footpoint twisting motions
Authors: Kliem, B.; Török, T.
2002ocnd.confE..25K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The evolution of coronal magnetic flux tubes under the
    influence of footpoint twisting motions
Authors: Török, T.; Kliem, B.
2001sps..proc..364T    Altcode:
  We present first results of an MHD simulation study of the quasi-static
  evolution of coronal magnetic flux tubes under the influence of
  vortex motions at their footpoints. An initial vacuum field of
  two sub-photospheric dipoles is subjected to slow vortex motions
  at the photospheric level, centred at the projected positions of
  the dipoles. The flux tube connecting the vortices becomes strongly
  twisted with time. This leads to an ascending and also laterally
  expanding motion of the upper parts of the tube, which takes an S-type,
  or sigmoidal, shape. Most of the field lines emanating at the sides
  of the vortices lean sidewards (to let the central flux tube ascend
  freely). If the amount of twist increases, the flux tube tends to take
  uniform width, i.e., field strength, along its upper parts. Decreasing
  the separation of the flux tube footpoints leads to the formation of
  a central current sheet between them.

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Title: Technical dictionary of spectroscopy and spectral
    analysis. English-French-German-Russian
Authors: Moritz, Heinrich; Toeroek, Tibor
1971tdss.book.....M    Altcode:
  No abstract at ADS