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Journal ArticleDOI

A Model for Solar Coronal Mass Ejections

01 Jan 1999-The Astrophysical Journal (IOP Publishing)-Vol. 510, Iss: 1, pp 485-493
TL;DR: In this article, a magnetic breakout model for the initiation of a solar coronal mass ejection (CME) was proposed, where reconnection between a sheared arcade and neighboring flux systems triggers the eruption.
Abstract: We propose a new model for the initiation of a solar coronal mass ejection (CME). The model agrees with two properties of CMEs and eruptive flares that have proved to be very difficult to explain with previous models: (1) very low-lying magnetic field lines, down to the photospheric neutral line, can open toward infinity during an eruption; and (2) the eruption is driven solely by magnetic free energy stored in a closed, sheared arcade. Consequently, the magnetic energy of the closed state is well above that of the posteruption open state. The key new feature of our model is that CMEs occur in multipolar topologies in which reconnection between a sheared arcade and neighboring flux systems triggers the eruption. In this "magnetic breakout" model, reconnection removes the unsheared field above the low-lying, sheared core flux near the neutral line, thereby allowing this core flux to burst open. We present numerical simulations that demonstrate our model can account for the energy requirements for CMEs. We discuss the implication of the model for CME/flare prediction.
Citations
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Journal ArticleDOI
TL;DR: The EUV Imaging Spectrometer (EIS) as mentioned in this paper is a two-element, normal incidence design with a backside-illuminated, thinned CCD, which has a significantly greater effective area than previous orbiting EUV spectrographs with typical active region 2 -5 s exposure times in the brightest lines.
Abstract: The EUV Imaging Spectrometer (EIS) on Hinode will observe solar corona and upper transition region emission lines in the wavelength ranges 170 – 210 A and 250 – 290 A. The line centroid positions and profile widths will allow plasma velocities and turbulent or non-thermal line broadenings to be measured. We will derive local plasma temperatures and densities from the line intensities. The spectra will allow accurate determination of differential emission measure and element abundances within a variety of corona and transition region structures. These powerful spectroscopic diagnostics will allow identification and characterization of magnetic reconnection and wave propagation processes in the upper solar atmosphere. We will also directly study the detailed evolution and heating of coronal loops. The EIS instrument incorporates a unique two element, normal incidence design. The optics are coated with optimized multilayer coatings. We have selected highly efficient, backside-illuminated, thinned CCDs. These design features result in an instrument that has significantly greater effective area than previous orbiting EUV spectrographs with typical active region 2 – 5 s exposure times in the brightest lines. EIS can scan a field of 6×8.5 arc min with spatial and velocity scales of 1 arc sec and 25 km s−1 per pixel. The instrument design, its absolute calibration, and performance are described in detail in this paper. EIS will be used along with the Solar Optical Telescope (SOT) and the X-ray Telescope (XRT) for a wide range of studies of the solar atmosphere.

1,050 citations


Cites background from "A Model for Solar Coronal Mass Ejec..."

  • ...Magnetic breakout scenarios (e.g., Antiochos, DeVore, and Klimchuk, 1999), require the removal of overlying magnetic field structures....

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Journal ArticleDOI
TL;DR: In this paper, the authors present observations of the magnetic field configuration and its transformation in six solar eruptive events that show good agreement with the standard bipolar model for eruptive flares.
Abstract: We present observations of the magnetic field configuration and its transformation in six solar eruptive events that show good agreement with the standard bipolar model for eruptive flares. The observations are X-ray images from the Yohkoh soft X-ray telescope (SXT) and magnetograms from Kitt Peak National Solar Observatory, interpreted together with the 1-8 Angstrom X-ray flux observed by Geostationary Operational Environmental Satellites (GOES). The observations yield the following interpretations: (1) Each event is a magnetic explosion that occurs in an initially closed single bipole in which the core field is sheared and twisted in the shape of a sigmoid, having an oppositely curved elbow on each end. The arms of the opposite elbows are sheared past each other so that they overlap and are crossed low above the neutral line in the middle of the bipole. The elbows and arms seen in the SXT images are illuminated strands of the sigmoidal core field, which is a continuum of sheared/twisted field that fills these strands as well as the space between and around them; (2) Although four of the explosions are ejective (appearing to blow open the bipole) and two are confined (appearing to be arrested within the closed bipole), all six begin the same way. In the SXT images, the explosion begins with brightening and expansion of the two elbows together with the appearance of short bright sheared loops low over the neutral line under the crossed arms and, rising up from the crossed arms, long strands connecting the far ends of the elbows; and (3) All six events are single-bipole events in that during the onset and early development of the explosion they show no evidence for reconnection between the exploding bipole and any surrounding magnetic fields. We conclude that in each of our events the magnetic explosion was unleashed by runaway tether-cutting via implosive/explosive reconnection in the middle of the sigmoid, as in the standard model. The similarity of the onsets of the two confined explosions to the onsets of the four ejective explosions and their agreement with the model indicate that runaway reconnection inside a sheared core field can begin whether or not a separate system of overlying fields, or the structure of the bipole itself, allows the explosion to be ejective. Because this internal reconnection apparently begins at the very start of the sigmoid eruption and grows in step with the explosion, we infer that this reconnection is essential for the onset and growth of the magnetic explosion in eruptive flares and coronal mass ejections.

1,019 citations

Journal ArticleDOI
TL;DR: In this article, the authors investigated the temporal relationship between coronal mass ejections (CMEs) and associated solar flares using the Large Angle and Spectrometric Coronagraph and the EUV Imaging Telescope observations combined with GOES soft X-ray observations.
Abstract: The temporal relationship between coronal mass ejections (CMEs) and associated solar flares is of great importance to understanding the origin of CMEs, but it has been difficult to study owing to the nature of CME detection. In this paper, we investigate this issue using the Large Angle and Spectrometric Coronagraph and the EUV Imaging Telescope observations combined with GOES soft X-ray observations. We present four well-observed events whose source regions are close to the limb such that we are able to directly measure the CMEs' initial evolution in the low corona (~ 1-3 R☉) without any extrapolation; this height range was not available in previous space-based coronagraph observations. The velocity-time profiles show that kinematic evolution of three of the four CMEs can be described in a three-phase scenario: the initiation phase, impulsive acceleration phase, and propagation phase. The initiation phase is characterized by a slow ascension with a speed less than 80 km s-1 for a period of tens of minutes. The initiation phase always occurs before the onset of the associated flare. Following the initiation phase, the CMEs display an impulsive acceleration phase that coincides very well with the flares' rise phase lasting for a few to tens of minutes. The acceleration of CMEs ceases near the peak time of the soft X-ray flares. The CMEs then undergo a propagation phase, which is characterized by a constant speed or slowly decreasing in speed. The acceleration rates in the impulsive acceleration phase are in the range of 100-500 m s-2. One CME (on 1997 November 6, associated with an X9.4 flare) does not show an initiation phase. It has an extremely large acceleration rate of 7300 m s-2. The possible causes of CME initiation and acceleration in connection with flares are explored.

744 citations

Journal ArticleDOI
TL;DR: A short review of some of the basic concepts related to the origin of coronal mass ejections (CMEs) can be found in this paper, where various ideas which have been put forward to explain the initiation of CMEs are categorized in terms of whether they are force-free or non-force-free and ideal or nonideal.
Abstract: This paper provides a short review of some of the basic concepts related to the origin of coronal mass ejections (CMEs). The various ideas which have been put forward to explain the initiation of CMEs are categorized in terms of whether they are force-free or non-force-free and ideal or nonideal. A few representative models of each category are examined to illustrate the principles involved. At the present time there is no model which is sufficiently developed to aid forecasters in their efforts to predict CMEs, but given the current pace of research, this situation could improve dramatically in the near future.

732 citations

Journal ArticleDOI
TL;DR: The Space Weather Modeling Framework (SWMF) as discussed by the authors provides a high-performance flexible framework for physics-based space weather simulations, as well as for various space physics applications.
Abstract: [1] The Space Weather Modeling Framework (SWMF) provides a high-performance flexible framework for physics-based space weather simulations, as well as for various space physics applications. The SWMF integrates numerical models of the Solar Corona, Eruptive Event Generator, Inner Heliosphere, Solar Energetic Particles, Global Magnetosphere, Inner Magnetosphere, Radiation Belt, Ionosphere Electrodynamics, and Upper Atmosphere into a high-performance coupled model. The components can be represented with alternative physics models, and any physically meaningful subset of the components can be used. The components are coupled to the control module via standardized interfaces, and an efficient parallel coupling toolkit is used for the pairwise coupling of the components. The execution and parallel layout of the components is controlled by the SWMF. Both sequential and concurrent execution models are supported. The SWMF enables simulations that were not possible with the individual physics models. Using reasonably high spatial and temporal resolutions in all of the coupled components, the SWMF runs significantly faster than real time on massively parallel supercomputers. This paper presents the design and implementation of the SWMF and some demonstrative tests. Future papers will describe validation (comparison of model results with measurements) and applications to challenging space weather events. The SWMF is publicly available to the scientific community for doing geophysical research. We also intend to expand the SWMF in collaboration with other model developers.

730 citations

References
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Journal ArticleDOI
TL;DR: In this paper, the authors outline a different paradigm of cause and effect that removes solar flares from their central position in the chain of events leading from the Sun to near-Earth space.
Abstract: Many years of research have demonstrated that large, nonrecurrent geomagnetic storms, shock wave disturbances in the solar wind, and energetic particle events in interplanetary space often occur in close association with large solar flares. This result has led to a pradigm of cause and effect - that large solar flares are the fundamental cause of these events in the near-Earth space environmemt. This paradigm, which I call 'the solar flare myth,' dominates the popular perception of the relationship between solar activity and interplanetary and geomagnetic events and has provided much of the pragmatic rationale for the study of the solar flare phenomenon. Yet there is good evidence that this paradigm is wrong and that flares do not generally play a central role in producing major transient disturbances in the near-Earth space environment. In this paper I outline a different paradigm of cause and effect that removes solar flares from their central position in the chain of events leading from the Sun to near-Earth space. Instead, this central role is given to events known as coronal mass ejections.

877 citations


"A Model for Solar Coronal Mass Ejec..." refers background in this paper

  • ...It is now widely recognized that coronal mass ejections (CMEs) are the most important manifestation of solar activity that drives the space weather near Earth (Gosling 1993, 1994)....

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Journal ArticleDOI
TL;DR: In this paper, the magnetic field expands outward in a process that opens the field lines and produces a tangential discontinuity, leading to an impulsive release of magnetic energy, fast flows, and the ejection of a plasmoid.
Abstract: The ideal and resistive properties of isolated large-scale coronal magnetic arcades are studied using axisymmetric solutions of the time-dependent magnetohydrodynamic (MHD) equations in spherical geometry. We examine how flares and coronal mass ejections may be initiated by sudden disruptions of the magnetic field. The evolution of coronal arcades in response to applied shearing photospheric flows indicates that disruptive behavior can occur beyond a critical shear. The disruption can be traced to ideal MHD magnetic nonequilibrium. The magnetic field expands outward in a process that opens the field lines and produces a tangential discontinuity in the magnetic field. In the presence of plasma resistivity, the resulting current sheet is the site of rapid reconnection, leading to an impulsive release of magnetic energy, fast flows, and the ejection of a plasmoid. We relate these results to previous studies of force-free fields and to the properties of the open-field configuration. We show that the field lines in an arcade are forced open when the magnetic energy approaches (but is still below) the open-field energy, creating a partially open field in which most of the field lines extend away from the solar surface. Preliminary application of this model to helmet streamers indicates that it is relevant to the initiation of coronal mass ejections.

500 citations

Journal ArticleDOI
TL;DR: An overview of observations of coronal mass ejections (CMEs) during the interval March 28, 1979 through December 31, 1981 is presented in this paper, where an introduction is provided to the instrument used in the observations, the method of identifying CMEs, the concepts of CME structural classes, CME importance categories, and the distribution of mass ejection among these classes and categories.
Abstract: An overview of observations of coronal mass ejections (CMEs) during the interval March 28, 1979 through December 31, 1981 is presented. An introduction is first provided to the instrument used in the observations, the method of identifying CMEs, the concepts of CME structural classes, CME importance categories, and the distribution of mass ejections among these classes and categories. The properties of CMEs are given for all mass ejections regardless of their structural classes or importance categories, and then for each class and category. After a brief discussion of the instrument duty cycle, the occurrence rate is presented for all CMEs and for major CMEs, for fast CMEs only, and finally for equatorial CMEs only. The results are compared to those obtained previously.

473 citations


"A Model for Solar Coronal Mass Ejec..." refers background in this paper

  • ...CMEs are huge ejected plasmoids, often with masses g and energies ergs, and frequentlyZ1016 Z1032 subtending more than 60¡ in position angle (see, e.g., Howard et al. 1985 ; Hundhausen 1997)....

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Journal ArticleDOI
TL;DR: In this article, a priori inequalities are defined which must be satisfied by the force-free equations, and upper bounds for the magnetic energy of the region provided the value of the magnetic normal component at the boundary of a region can be shown to decay sufficiently fast at infinity.
Abstract: Techniques for solving boundary value problems (BVP) for a force free magnetic field (FFF) in infinite space are presented. A priori inequalities are defined which must be satisfied by the force-free equations. It is shown that upper bounds may be calculated for the magnetic energy of the region provided the value of the magnetic normal component at the boundary of the region can be shown to decay sufficiently fast at infinity. The results are employed to prove a nonexistence theorem for the BVP for the FFF in the spatial region. The implications of the theory for modeling the origins of solar flares are discussed.

333 citations


"A Model for Solar Coronal Mass Ejec..." refers background or methods in this paper

  • ...As emphasized by a number of authors (see, e.g., Aly 1984 ; Klimchuk & Sturrock 1989 ; Wolfson & Verma 1991), a low-b system like the corona is highly sensitive to boundary conditions at the base, and the application of inappropriate conditions can easily lead to erroneous conclusions about the…...

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  • ...Note that the boundary conditions we use are exactly the ones used by Aly (1984), Sturrock (1989), and others in deriving the energy limit....

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  • ...In fact, Aly (1984) and Sturrock (1991) have claimed, on the basis of mathematical arguments, that the maximum energy state of any force-free Ðeld is the fully open Ðeld (Aly 1984, 1991 ; Sturrock 1991)....

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Journal ArticleDOI
TL;DR: In this article, a magneto-frictional method was proposed to calculate magnetic field configurations in which the Lorentz force j x B is everywhere zero, subject to specified boundary conditions.
Abstract: The problem under discussion is that of calculating magnetic field configurations in which the Lorentz force j x B is everywhere zero, subject to specified boundary conditions. We choose to represent the magnetic field in terms of Clebsch variables in the form B = grad alpha x grad beta. These variables are constant on any field line so that each field line is labeled by the corresponding values of alpha and beta. When the field is described in this way, the most appropriate choice of boundary conditions is to specify the values of alpha and beta on the bounding surface. We show that such field configurations may be calculated by a magneto-frictional method. We imagine that the field lines move through a stationary medium, and that each element of magnetic field is subject to a frictional force parallel to and opposing the velocity of the field line. This concept leads to an iteration procedure for modifying the variables alpha and beta, that tends asymptotically towards the force-free state. We apply the method first to a simple problem in two rectangular dimensions, and then to a problem of cylindrical symmetry that was previously discussed by Barnes and Sturrock (1972). In one important respect, our new results differ from the earlier results of Barnes and Sturrock, and we conclude that the earlier article was in error.

256 citations


"A Model for Solar Coronal Mass Ejec..." refers methods in this paper

  • ...The code solves the force-free equations ($ Â B) Â B \ 0 (1) using an Euler potential representation for the Ðeld (Yang et al. 1986)....

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