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Slow Rise and Partial Eruption of a Double-Decker Filament. II. A Double Flux Rope Model  

Bernhard Kliem   Submitted: 2014-07-13 05:34

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 & Demoulin (1999) 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 being 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 (Liu et al. 2012). 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.

Authors: B. Kliem, T. Toeroek, V. S. Titov, R. Lionello, J. A. Linker, R. Liu, C. Liu, & H. Wang
Projects: None

Publication Status: ApJ, accepted
Last Modified: 2014-07-13 18:37
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Catastrophe versus instability for the eruption of a toroidal solar magnetic flux rope  

Bernhard Kliem   Submitted: 2014-07-11 09:04

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.

Authors: B. Kliem, J. Lin, T. G. Forbes, E. R. Priest, & T. Török
Projects: None

Publication Status: Published in ApJ 789, 46, 2014
Last Modified: 2014-07-11 14:33
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Magnetohydrodynamic Modeling of the Solar Eruption on 2010 April 8  

Bernhard Kliem   Submitted: 2014-07-11 09:00

The structure of the coronal magnetic field prior to eruptive processes and the conditions for the onset of eruption are important issues that can be addressed through studying the magnetohydrodynamic stability and evolution of nonlinear force-free field (NLFFF) models. This paper uses data-constrained NLFFF models of a solar active region that erupted on 2010 April 8 as initial condition in MHD simulations. These models, constructed with the techniques of flux rope insertion and magnetofrictional relaxation, include a stable, an approximately marginally stable, and an unstable configuration. The simulations confirm previous related results of magnetofrictional relaxation runs, in particular that stable flux rope equilibria represent key features of the observed pre-eruption coronal structure very well and that there is a limiting value of the axial flux in the rope for the existence of stable NLFFF equilibria. The specific limiting value is located within a tighter range, due to the sharper discrimination between stability and instability by the MHD description. The MHD treatment of the eruptive configuration yields very good agreement with a number of observed features like the strongly inclined initial rise path and the close temporal association between the coronal mass ejection and the onset of flare reconnection. Minor differences occur in the velocity of flare ribbon expansion and in the further evolution of the inclination; these can be eliminated through refined simulations. We suggest that the slingshot effect of horizontally bent flux in the source region of eruptions can contribute significantly to the inclination of the rise direction. Finally, we demonstrate that the onset criterion formulated in terms of a threshold value for the axial flux in the rope corresponds very well to the threshold of the torus instability in the considered active region.

Authors: B. Kliem, Y. N. Su, A. A. van Ballegooijen, & E. E. DeLuca
Projects: Hinode/XRT,SDO-AIA,SDO-HMI,STEREO

Publication Status: Published in ApJ 779, 129, 2013
Last Modified: 2014-07-11 14:34
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Observations of flux rope formation prior to coronal mass ejections  

Bernhard Kliem   Submitted: 2014-07-11 08:55

Understanding the magnetic configuration of the source regions of coronal mass ejections (CMEs) is vital in order to determine the trigger and driver of these events. Observations of four CME productive active regions are presented here, which indicate that the pre-eruption magnetic configuration is that of a magnetic flux rope. The flux ropes are formed in the solar atmosphere by the process known as flux cancellation and are stable for several hours before the eruption. The observations also indicate that the magnetic structure that erupts is not the entire flux rope as initially formed, raising the question of whether the flux rope is able to undergo a partial eruption or whether it undergoes a transition in specific flux rope configuration shortly before the CME.

Authors: L. M. Green & B. Kliem
Projects: GOES X-rays ,Hinode/XRT,Yohkoh-SXT

Publication Status: Published in Proc. IAU Symp. 300, 209, 2013
Last Modified: 2014-07-11 14:34
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CME development in the corona and interplanetary medium: A multi-wavelength approach  

Bernhard Kliem   Submitted: 2014-07-11 08:47

This review focuses on the so called three-part CMEs which essentially represent the standard picture of a CME eruption. It is shown how the multi-wavelength observations obtained in the last decade, especially those with high cadence, have validated the early models and contributed to their evolution. These observations cover a broad spectral range including the EUV, white-light, and radio domains.

Authors: M. Pick & B. Kliem
Projects: SDO-AIA,SoHO-LASCO,STEREO

Publication Status: Published in EAS Publ. Ser. 55, 299
Last Modified: 2014-07-11 14:34
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A Parametric Study of Erupting Flux Rope Rotation. Modeling the ''Cartwheel CME'' on 9 April 2008  

Bernhard Kliem   Submitted: 2011-12-16 08:03

The rotation of erupting filaments in the solar corona is addressed through aparametric simulation study of unstable, rotating flux ropes in bipolarforce-free initial equilibrium. The Lorentz force due to the external shearfield component and the relaxation of tension in the twisted field are themajor contributors to the rotation in this model, while reconnection with theambient field is of minor importance. Both major mechanisms writhe the fluxrope axis, converting part of the initial twist helicity, and produce rotationprofiles which, to a large part, are very similar in a range of shear-twistcombinations. A difference lies in the tendency of twist-driven rotation tosaturate at lower heights than shear-driven rotation. For parameterscharacteristic of the source regions of erupting filaments and coronal massejections, the shear field is found to be the dominant origin of rotations inthe corona and to be required if the rotation reaches angles of order 90degrees and higher; it dominates even if the twist exceeds the threshold of thehelical kink instability. The contributions by shear and twist to the totalrotation can be disentangled in the analysis of observations if the rotationand rise profiles are simultaneously compared with model calculations. Theresulting twist estimate allows one to judge whether the helical kinkinstability occurred. This is demonstrated for the erupting prominence in the'Cartwheel CME' on 9 April 2008, which has shown a rotation of approx 115degrees up to a height of 1.5 R_sun above the photosphere. Out of a range ofinitial equilibria which include strongly kink-unstable (twist Phi=5pi), weaklykink-unstable (Phi=3.5pi), and kink-stable (Phi=2.5pi) configurations, only theevolution of the weakly kink-unstable flux rope matches the observations intheir entirety.

Authors: B. Kliem, T. Toeroek, W. T. Thompson
Projects: STEREO

Publication Status: Solar Physics, submitted
Last Modified: 2011-12-19 09:10
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3D Reconstruction of a Rotating Erupting Prominence  

Bernhard Kliem   Submitted: 2011-12-16 08:00

A bright prominence associated with a coronal mass ejection (CME) was seenerupting from the Sun on 9 April 2008. This prominence was tracked by both theSolar Terrestrial Relations Observatory (STEREO) EUVI and COR1 telescopes, andwas seen to rotate about the line of sight as it erupted; therefore, the eventhas been nicknamed the 'Cartwheel CME'. The threads of the prominence in thecore of the CME quite clearly indicate the structure of a weakly to moderatelytwisted flux rope throughout the field of view, up to heliocentric heights of 4solar radii. Although the STEREO separation was 48 degrees, it was possible tomatch some sharp features in the later part of the eruption as seen in the 304{AA} line in EUVI and in the Hα -sensitive bandpass of COR1 by both STEREOAhead and Behind. These features could then be traced out in three-dimensionalspace, and reprojected into a view in which the eruption is directed towardsthe observer. The reconstructed view shows that the alignment of the prominenceto the vertical axis rotates as it rises up to a leading-edge height of approx2.5 solar radii, and then remains approximately constant. The alignment at 2.5solar radii differs by about 115 degrees from the original filament orientationinferred 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 rotationis reached within approx 0.5 solar radii above the photosphere. These featuresare well reproduced by numerical simulations of an unstable moderately twistedflux rope embedded in external flux with a relatively strong shear fieldcomponent.

Authors: W. T. Thompson, B. Kliem, T. Toeroek
Projects: STEREO

Publication Status: published in Solar Physics (Online First)
Last Modified: 2011-12-19 09:10
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Photospheric flux cancellation and associated flux rope formation and eruption  

Bernhard Kliem   Submitted: 2010-11-05 08:52

Aims: We study an evolving bipolar active region that exhibits flux cancellation at the internal polarity inversion line, the formation of a soft X-ray sigmoid along the inversion line and a coronal mass ejection. The aim is to investigate the quantity of flux cancellation that is involved in flux rope formation in the time period leading up to the eruption. Methods: The active region is studied using its extreme ultraviolet and soft X-ray emissions as it evolves from a sheared arcade to flux rope configuration. The evolution of the photospheric magnetic field is described and used to estimate how much flux is reconnected into the flux rope. Results: About one third of the active region flux cancels at the internal polarity inversion line in the 2.5 days leading up to the eruption. In this period, the coronal structure evolves from a weakly to a highly sheared arcade and then to a sigmoid that crosses the inversion line in the inverse direction. These properties suggest that a flux rope has formed prior to the eruption. The amount of cancellation implies that up to 60% of the active region flux could be in the body of the flux rope. We point out that only part of the cancellation contributes to the flux in the rope if the arcade is only weakly sheared, as in the first part of the evolution. This reduces the estimated flux in the rope to ~ 30% or less of the active region flux. We suggest that the remaining discrepancy between our estimate and the limiting value of ~ 10% of the active region flux, obtained previously by the flux rope insertion method, results from the incomplete coherence of the flux rope, due to nonuniform cancellation along the polarity inversion line. A hot linear feature is observed in the active region which rises as part of the eruption and then likely traces out field lines close to the axis of the flux rope. The flux cancellation and changing magnetic connections at one end of this feature suggest that the flux rope reaches coherence by reconnection shortly before and early in the impulsive phase of the associated flare. The sigmoid is destroyed in the eruption but reforms quickly, with the amount of cancellation involved being much smaller than in the course of its original formation.

Authors: L. M. Green, B. Kliem, A. J. Wallace
Projects: Hinode/EIS,Hinode/XRT,SoHO-MDI,SoHO-LASCO

Publication Status: Astron. Astrophys., in press
Last Modified: 2010-11-08 07:34
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Reconnection of a kinking flux rope triggering the ejection of a microwave and hard X-ray source. I. Observations and interpretation  

Bernhard Kliem   Submitted: 2010-08-09 03:21

Imaging microwave observations of an eruptive, partially occulted solar flare on 18 April 2001 suggest that the global structure of the event can be described by the helical kink instability of a twisted magnetic flux rope. This model is suggested by the inverse gamma shape of the source exhibiting crossing legs of a rising flux loop and by evidence that the legs interact at or near the crossing point. The interaction is reflected by the location of peak brightness near the crossing point and by the formation of superimposed compact nonthermal sources most likely at or near the crossing point. These sources propagate upward along both legs, merge into a single, bright source at the top of the structure, and continue to rise at a velocity >1000 km s-1. The compact sources trap accelerated electrons which radiate in the radio and hard X-ray ranges. This suggests that they are plasmoids, although their internal structure is not revealed by the data. They exhibit variations of the radio brightness temperature at a characteristic time scale of ~ 40 s, anti-correlated to their area, which also support their interpretation as plasmoids. Their propagation path differs from the standard scenario of plasmoid formation and propagation in the flare current sheet, suggesting the helical current sheet formed by the instability instead.

Authors: M. Karlický and B. Kliem
Projects:

Publication Status: Solar Physics, in press
Last Modified: 2010-08-09 08:33
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Reconnection of a kinking flux rope triggering the ejection of a microwave and hard X-ray source. II. Numerical modeling  

Bernhard Kliem   Submitted: 2010-08-09 03:16

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 Phigtrsim6pi. Such 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.

Authors: B. Kliem, M. G. Linton, T. Toeroek, M. Karlický
Projects:

Publication Status: Solar Physics, in press
Last Modified: 2010-08-09 08:34
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Evidence for Mixed Helicity in Erupting Filaments  

Bernhard Kliem   Submitted: 2010-08-09 03:11

Erupting filaments are sometimes observed to undergo a rotation about the vertical direction as they rise. This rotation of the filament axis is generally interpreted as a conversion of twist into writhe in a kink-unstable magnetic flux rope. Consistent with this interpretation, the rotation is usually found to be clockwise (as viewed from above) if the post-eruption arcade has right-handed helicity, but counterclockwise if it has left-handed helicity. Here, we describe two non-active-region filament events recorded with the Extreme-Ultraviolet Imaging Telescope on the Solar and Heliospheric Observatory in which the sense of rotation appears to be opposite to that expected from the helicity of the post-event arcade. Based on these observations, we suggest that the rotation of the filament axis is, in general, determined by the net helicity of the erupting system, and that the axially aligned core of the filament can have the opposite helicity sign to the surrounding field. In most cases, the surrounding field provides the main contribution to the net helicity. In the events reported here, however, the helicity associated with the filament ''barbs'' is opposite in sign to and dominates that of the overlying arcade.

Authors: K. Muglach, Y.-M. Wang, B. Kliem
Projects: SoHO-EIT,SoHO-MDI

Publication Status: ApJ 703, 976 (2009)
Last Modified: 2010-08-09 07:49
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Endpoint Brightenings in Erupting Filaments  

Bernhard Kliem   Submitted: 2009-06-28 20:00

Two well known phenomena associated with erupting filaments are the transient coronal holes that form on each side of the filament channel and the bright post-event arcade with its expanding double row of footpoints. Here we focus on a frequently overlooked signature of filament eruptions: the spike- or fan-shaped brightenings that appear to mark the far endpoints of the filament. From a sample of non-active-region filament events observed with the Extreme-Ultraviolet Imaging Telescope on the Solar and Heliospheric Observatory, we find that these brightenings usually occur near the outer edges of the transient holes, in contrast to the post-event arcades, which define their inner edges. The endpoints are often multiple and are rooted in and around strong network flux well outside the filament channel, a result that is consistent with the axial field of the filament being much stronger than the photospheric field inside the channel. The extreme ultraviolet brightenings, which are most intense at the time of maximum outward acceleration of the filament, can be used to determine unambiguously the direction of the axial field component from longitudinal magnetograms. Their location near the outer boundary of the transient holes suggests that we are observing the footprints of the current sheet formed at the leading edge of the erupting filament, as distinct from the vertical current sheet behind the filament which is the source of the post-event arcade.

Authors: Y.-M. Wang, K. Muglach, and B. Kliem
Projects: SoHO-EIT,SoHO-MDI,SoHO-LASCO

Publication Status: ApJ 699, 133 (2009)
Last Modified: 2009-06-29 09:40
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Flux Rope Formation Preceding Coronal Mass Ejection Onset  

Bernhard Kliem   Submitted: 2009-06-28 18:29

We analyse the evolution of a sigmoidal (S shaped) active region toward eruption, which includes a coronal mass ejection (CME) but leaves part of the filament in place. The X-ray sigmoid is found to trace out three different magnetic topologies in succession: a highly sheared arcade of coronal loops in its long-lived phase, a bald-patch separatrix surface (BPSS) in the hours before the CME, and the first flare loops in its major transient intensity enhancement. The coronal evolution is driven by photospheric changes which involve the convergence and cancellation of flux elements under the sigmoid and filament. The data yield unambiguous evidence for the existence of a BPSS, and hence a flux rope, in the corona prior to the onset of the CME.

Authors: L. M. Green and B. Kliem
Projects: Yohkoh-SXT,SoHO-MDI

Publication Status: ApJ Letters, in press
Last Modified: 2009-06-29 09:40
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Torus instability  

Bernhard Kliem   Submitted: 2006-08-04 13:23

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.

Authors: B. Kliem and T. Toeroek
Projects:

Publication Status: Phys. Rev. Lett. 96, 255002, 2006
Last Modified: 2006-09-11 09:08
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Testing the alphabest magnetic field extrapolation method with nonlinear force-free fields  

Bernhard Kliem   Submitted: 2004-12-15 15:38

We apply the alphabest magnetic field extrapolation method to two complementary nonlinear force-free models of solar active regions containing a twisted flux rope, in order to demonstrate that the method strongly underestimates the current helicity density in equilibrium flux ropes with twists exceeding Phisimpi. This behaviour results from the limit set on the force-free parameter α by the employed linear force-free field and from the compromise in fitting a linear to a nonlinear force-free field embodied by the method. The result holds for flux ropes with and without a net current. The α _mathrm{best} values obtained for nonlinear fields scatter strongly if the magnetogram size or the threshold field strength used in determining α _mathrm{best} are varied. The scatter can, in some cases, even lead to a sign of α _mathrm{best} opposite to that of α in the core of the flux rope.

Authors: B. Kliem and G. Valori
Projects: None

Publication Status: ApJ, submitted
Last Modified: 2004-12-15 15:38
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Extrapolation of a nonlinear force-free field containing a highly twisted magnetic loop  

Bernhard Kliem   Submitted: 2004-12-15 15:33

The stress-and-relax method for the extrapolation of nonlinear force-free coronal magnetic fields from photospheric vector magnetograms is formulated and implemented in a manner analogous to the evolutionary extrapolation method. The technique is applied to a numerically constructed force-free equilibrium that has a simple bipolar structure of the normal field component at the bottom but contains a highly twisted loop and a shear (current) layer, with a smooth but strong variation of the force-free parameter α in the magnetogram. A standard linear force-free extrapolation of this magnetogram, using the so-called α _mathrm{best} value, is found to fail in reproducing the twisted loop (or flux rope) and the shear layer; it yields a loop pair instead and the shear is not concentrated in a layer. With the nonlinear extrapolation technique, the given equilibrium is readily reconstructed to a high degree of accuracy if the magnetogram is sufficiently resolved. A parametric study quantifies the requirements on the resolution for a successful nonlinear extrapolation. Permitting magnetic reconnection by a controlled use of resistivity improved the extrapolation of a magnetogram which contained structures with scales at the resolution limit.

Authors: G. Valori, B. Kliem, R. Keppens
Projects: None

Publication Status: A&A, in press
Last Modified: 2004-12-15 15:33
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Formation of current sheets and sigmoidal structure by the kink instability of a magnetic loop  

Bernhard Kliem   Submitted: 2003-11-06 17:30

We study dynamical consequences of the kink instability of a twisted coronal flux rope, using the force-free coronal loop model by Titov & D'emoulin (1999) 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.

Authors: B. Kliem, V. S. Titov, and T. Toeroek
Projects: None

Publication Status: Astron. Astrophys. Lett., accepted
Last Modified: 2003-11-07 15:37
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Ideal kink instability of a magnetic loop equilibrium  

Bernhard Kliem   Submitted: 2003-11-06 17:26

The force-free coronal loop model by Titov & D'emoulin (1999) 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 Phi gtrsim 3.5pi (at a loop aspect ratio of approx 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. (See animation at http://www.aip.de/~kli/Fi252.gif)

Authors: T. Toeroek, B. Kliem, and V. S. Titov
Projects:

Publication Status: Astron. Astrophys. Lett., accepted
Last Modified: 2003-11-07 15:51
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The evolution of twisting coronal magnetic flux tubes  

Bernhard Kliem   Submitted: 2003-11-06 17:14

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 Sturrock et al. (1995) 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 < Phi_mathrm{c} < 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.

Authors: T. Toeroek and B. Kliem
Projects:

Publication Status: Astron. Astrophys. 406, 1043 (2003)
Last Modified: 2003-11-21 10:28
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Correlated dynamics of hot and cool plasmas in the main phase of a solar flare  

Bernhard Kliem   Submitted: 2002-03-04 11:58

We report far-ultraviolet observations of a solar limb flare obtained by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer. At a fixed pointing of the slit above the limb, spectra were simultaneously obtained in several emission lines that covered a wide temperature range from approx!104 to approx!107 K. The temporal evolution of the spectra revealed, for the first time, a high degree of correlation between the dynamical behavior of hot (Tsim107 K) and cool (Tsim104 K) coronal material during the main phase of a flare. We note that the data did not show any indication of the presence of a prominence. Hot and cool plasmas brightened at nearly the same location. Their Doppler shifts, which were opposite to each other, reached peak values simultaneously. Thereafter, the two components showed anti-correlated, rapidly damped, and oscillatory Doppler shifts and a very similar decay of the line widths, but with the cool plasma reaching maximum brightness before the hot plasma. This behavior points to an active role for cool plasma in the dynamics of this flare, different from the usual picture of passive cooling after the impulsive phase. We suggest a model in which the localized cooling of coronal plasma by the thermal instability triggers magnetic reconnection through the resulting enhanced resistivity, the combined processes leading to the correlated dynamics of hot and cool plasmas in a loop-loop interaction geometry.

Authors: B. Kliem, I. E. Dammasch, W. Curdt, and K. Wilhelm
Projects:

Publication Status: ApJ Lett (in press)
Last Modified: 2002-03-04 11:58
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Abstracts by Author
Slow Rise and Partial Eruption of a Double-Decker Filament. II. A Double Flux Rope Model
Catastrophe versus instability for the eruption of a toroidal solar magnetic flux rope
Magnetohydrodynamic Modeling of the Solar Eruption on 2010 April 8
Observations of flux rope formation prior to coronal mass ejections
CME development in the corona and interplanetary medium: A multi-wavelength approach
A Parametric Study of Erupting Flux Rope Rotation. Modeling the ''Cartwheel CME'' on 9 April 2008
3D Reconstruction of a Rotating Erupting Prominence
Photospheric flux cancellation and associated flux rope formation and eruption
Reconnection of a kinking flux rope triggering the ejection of a microwave and hard X-ray source. I. Observations and interpretation
Reconnection of a kinking flux rope triggering the ejection of a microwave and hard X-ray source. II. Numerical modeling
Evidence for Mixed Helicity in Erupting Filaments
Endpoint Brightenings in Erupting Filaments
Flux Rope Formation Preceding Coronal Mass Ejection Onset
Torus instability
Testing the alphabest magnetic field extrapolation method with nonlinear force-free fields
Extrapolation of a nonlinear force-free field containing a highly twisted magnetic loop
Formation of current sheets and sigmoidal structure by the kink instability of a magnetic loop
Ideal kink instability of a magnetic loop equilibrium
The evolution of twisting coronal magnetic flux tubes
Correlated dynamics of hot and cool plasmas in the main phase of a solar flare
Solar flare radio pulsations as a signature of dynamic magnetic reconnection
Three-dimensional spontaneous magnetic reconnection in neutral current sheets

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