Author name code: toeroek ADS astronomy entries on 2022-09-14 author:"Toeroek, Tibor" ------------------------------------------------------------------------ Title: A Magnetogram-matching Method for Energizing Magnetic Flux Ropes Toward Eruption Authors: Titov, V. S.; Downs, C.; Török, T.; Linker, J. A. Bibcode: 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. 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 Bibcode: 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. Title: Suppression of Torus Instability on Cool Stars Authors: Sun, Xudong; Derosa, Marc; Torok, Tibor Bibcode: 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. Title: Early Dynamics and Trajectories of CMEs Authors: Zhang, Jie; Torok, Tibor; Nikou, Eleni; Nazmus Sakib, Md; Dhakal, Suman Bibcode: 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? Title: The 3D magnetic structure of CMEs throughout the extended solar corona Authors: Palmerio, Erika; Downs, Cooper; Torok, Tibor; Ben-Nun, Michal Bibcode: 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. Title: The Pre-Eruptive Structure and Initiation Mechanism(s) of CMEs Authors: Torok, Tibor Bibcode: 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. 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. Bibcode: 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°).
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.
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.
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.
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.

Movie associated to Fig. 2 is available at https://www.aanda.org Title: A Model of Homologous Confined and Ejective Eruptions Involving Kink Instability and Flux Cancellation Authors: Hassanin, Alshaimaa; Kliem, Bernhard; Seehafer, Norbert; Török, Tibor Bibcode: 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. Title: Torus-stable zone above starspots Authors: Sun, Xudong; Török, Tibor; DeRosa, Marc L. Bibcode: 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. Title: Magnetogram-matching Energization and Eruption of Magnetic Flux Ropes Authors: Titov, Viacheslav; Downs, Cooper; Torok, Tibor; Linker, Jon Bibcode: 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. Title: Propagation and Deflection of CMEs in Different Background Magnetic Fields Authors: Ben-Nun, Michal; Torok, Tibor; Downs, Cooper; Caplan, Ronald; Lionello, Roberto Bibcode: 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. Title: Theory and Models of Flare/CME Onset Via Flux Emergence and/or Shear Flows Authors: Linton, Mark; Torok, Tibor; Lynch, Benjamin Bibcode: 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 Title: Evolution of Non-neutralized Electric Currents in Eruptive Solar Active Regions Authors: Prazak, Michael; Downs, Cooper; Torok, Tibor; Jiong, Qiu; Titov, Viacheslav Bibcode: 2021AGUFMSH35B2036P Altcode: We study the evolution of several solar active regions (ARs) that produced both fast (>600 km/s) and slow (<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). 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 Bibcode: 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. 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 Bibcode: 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. 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 Bibcode: 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? Title: Torus-Stable Zone Above Starspots Authors: Sun, Xudong; Torok, Tibor; DeRosa, Marc Bibcode: 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. 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. Bibcode: 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. Bibcode: 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.

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.

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.

*Research supported by NSF, NASA, and AFOSR Title: Torus-Stable Zone Above Starspots Authors: Sun, X.; Torok, T.; DeRosa, M. Bibcode: 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 hc increases with the bipole size a, the dipole field with harmonic coefficient g10, and the source surface radius Rs where the magnetic field becomes radial. The value of hc, 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 Rs. 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. Bibcode: 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 Bibcode: 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 hc increases with the bipole size a, the dipole field with harmonic coefficient g10, and the source surface radius Rs where the magnetic field becomes radial. The value of hc, 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 Rs. 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. Bibcode: 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⊙, 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 Bibcode: 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 > 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. Bibcode: 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.

* 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. Bibcode: 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. Bibcode: 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. Bibcode: 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?

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.

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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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-1. 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. Bibcode: 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.

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. Bibcode: 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. Bibcode: 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 s 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. Bibcode: 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. Bibcode: 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. Bibcode: 2019AGUFMSH33B3391Q Altcode: Eruptions of a magnetic flux rope in the solar corona can be triggered by certain magnetohydrodynamic (MHD) instabilities, such as the helical

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 Bibcode: 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.

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 Bibcode: 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?

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.

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 Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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.

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 Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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 Bibcode: 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 Bibcode: 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 & 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 Bibcode: 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 Bibcode: 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 Bibcode: 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 Bibcode: 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 (<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 (<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 Bibcode: 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 Bibcode: 2018tess.conf10905L Altcode: Partially Open Fields and Solar Eruptions*

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.

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 & Low ApJ 1992; Hu, ApJ 2004; Aly & 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.

*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 Bibcode: 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 Bibcode: 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 1033 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-1, 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 Bibcode: 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 1033 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-1, 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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 > 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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.

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.

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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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'(2012, ApJ, 756, 59) Authors: Liu, Rui; Kliem, Bernhard; Török, Tibor; Liu, Chang; Titov, Viacheslav S.; Lionello, Roberto; Linker, Jon A.; Wang, Haimin Bibcode: 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. Bibcode: 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.

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.

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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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 Bibcode: 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.

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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 & 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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 (1010 cm-3) 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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 Bibcode: 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 Bibcode: 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 Bibcode: 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).

Work supported by Lockheed Martin, NASA's Heliophysics Theory and SR&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 Bibcode: 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 Bibcode: 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 Bibcode: 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 Bibcode: 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 ⊙-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. Bibcode: 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&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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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∘ up to a height of 1.5 R⊙ 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. Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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&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 Bibcode: 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&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 Bibcode: 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 Bibcode: 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 Bibcode: 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. Title: Observation & 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. Bibcode: 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

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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 & 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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.

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. Bibcode: 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.

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.

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 Bibcode: 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. Bibcode: 2011shin.confE.131T Altcode: The Solar Dynamics Observatory observed on 1-2 August 2010 an interesting sequence of coronal mass ejections (CMEs) (Schrijver & 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.

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. Bibcode: 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. Bibcode: 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

several individual eruptions occurring

almost simultaneously in different source regions. The close temporal vicinity of the individual eruptions in such events indicates the

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. Bibcode: 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. Bibcode: 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. Bibcode: 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. 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. Bibcode: 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. Bibcode: 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. Title: Writhing and rotation of erupting prominences and CMEs Authors: Torok, T.; Kliem, B.; Thompson, W. T.; Berger, M. A. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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.
Aims: Here we perform a quantitative investigation of these questions relevant for coronal flux ropes.
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).
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.
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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Title: Ejective events from a complex active region Authors: Mandrini, Cristina H.; Chandra, Ramesh; Pariat, Etienne; Schmieder, Brigitte; Demoulin, Pascal; Toeroek, Tibor; Uddin, Wahab Bibcode: 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. 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. Bibcode: 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. Bibcode: 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-1, whereas downflows of up to 30 km s-1 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-1 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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.

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.

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. Bibcode: 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.
Methods: We perform 3D numerical experiments by solving the time-dependent and resistive MHD equations.
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. Bibcode: 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 & 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. Bibcode: 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.

Unfortunately, the coronal magnetic field is not directly measurable at present, and therefore it is difficult to verify the validity of different CME models.

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.

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.

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.

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)).

Therefore, the TD solution is by far the most realistic analytical equilibrium available to date for the modeling of solar active regions.

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.

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.

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.

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.

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. Bibcode: 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. Bibcode: 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.

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.

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 & 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. Bibcode: 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. Bibcode: 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.

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.

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. Bibcode: 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 tm 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 Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Title: Torus Instability Authors: Kliem, B.; Török, T. Bibcode: 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. Title: Confined and Ejective Eruptions of Kink-unstable Flux Ropes Authors: Török, T.; Kliem, B. Bibcode: 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. 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 Bibcode: 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. Title: The Kink Instability in Solar Eruptions Authors: Török, T.; Kliem, B. Bibcode: 2004ESASP.575...56T Altcode: 2004soho...15...56T No abstract at ADS Title: The kink instability of a coronal magnetic loop as a trigger mechanism for solar eruptions Authors: Török, T.; Kliem, B. Bibcode: 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. Title: Ideal kink instability of a magnetic loop equilibrium Authors: Török, T.; Kliem, B.; Titov, V. S. Bibcode: 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. Title: Formation of current sheets and sigmoidal structure by the kink instability of a magnetic loop Authors: Kliem, B.; Titov, V. S.; Török, T. Bibcode: 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. Title: The kink instability of a coronal magnetic loop as a trigger mechanism for solar eruptions Authors: Török, T.; Kliem, B.; Titov, V. S. Bibcode: 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. Title: Instabilität magnetischer Flußröhren in solaren Eruptionen Title: Instabilität magnetischer Flußröhren in solaren Eruptionen Authors: Török, Tibor Bibcode: 2004PhDT.......150T Altcode: No abstract at ADS Title: The evolution of twisting coronal magnetic flux tubes Authors: Török, T.; Kliem, B. Bibcode: 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 <Phic<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. 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. Bibcode: 2003ANS...324...73K Altcode: 2003ANS...324..I16K No abstract at ADS Title: The evolution of coronal magnetic flux tubes twisted by photospheric vortex motions Authors: Török, T.; Kliem, B. Bibcode: 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 < Φc < 3.0π. Title: The evolution of coronal magnetic flux tubes subject to footpoint twisting motions Authors: Kliem, B.; Török, T. Bibcode: 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. Bibcode: 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. Title: Technical dictionary of spectroscopy and spectral analysis. English-French-German-Russian Authors: Moritz, Heinrich; Toeroek, Tibor Bibcode: 1971tdss.book.....M Altcode: No abstract at ADS