Confined and ejective eruptions of kink-unstable flux ropes

a r X i v :a s t r o -p h /0507662v 2 24 A u g 2005

MS 19378,J ULY 1,2005

Preprint typeset using L A T E X style emulateapj v.6/22/04

CONFINED AND EJECTIVE ERUPTIONS OF KINK-UNSTABLE FLUX ROPES

T.T ?R?K 1

AND

B.K LIEM 2

Received 2005March 4;accepted 2005July 18

ABSTRACT

The ideal helical kink instability of a force-free coronal magnetic ?ux rope,anchored in the photosphere,is studied as a model for solar https://www.wendangku.net/doc/e77019305.html,ing the ?ux rope model of Titov &Démoulin (1999)as the initial condition in MHD simulations,both the development of helical shape and the rise pro?le of a con?ned (or failed)?lament eruption (on 2002May 27)are reproduced in very good agreement with the observations.By modifying the model such that the magnetic ?eld decreases more rapidly with height above the ?ux 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 pro?le of a fast coronal mass ejection (CME)(on 2001May 15).This con?rms that the helical kink instability of a twisted magnetic ?ux 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 ?eld with height is a main factor in deciding whether the instability leads to a con?ned event or to a CME.

Subject headings:Instabilities –MHD –Sun:corona –Sun:?ares –Sun:coronal mass ejections (CMEs)

1.INTRODUCTION

Large-scale solar eruptions occur as ?ares,?lament (or prominence)eruptions,and coronal mass ejections (CMEs).Despite their different observational appearance,it is believed that these phenomena are manifestations of the same physical processes,which involve the disruption of the coronal mag-netic ?eld.Indeed,in the largest eruptions (eruptive ?ares)usually all three phenomena are observed.The theory of the main phase of such events,referred to as the “standard model”of eruptive ?ares (e.g.,Shibata 1999),is quite well estab-lished.However,their initiation as well as the mechanism of upward acceleration are still unclear.A variety of theoretical models have been proposed to explain the impulsive onset and initial evolution of solar eruptions (see,e.g.,Forbes 2000).Here we focus on a ?ux rope instability model.This is mo-tivated by the observation that solar eruptions often show the phenomenology of a loop-shaped magnetic ?ux system with ?xed footpoints at the coronal base and signatures of magnetic twist.Furthermore,erupting ?laments very often develop a clearly helical axis shape in the course of the eruption,which is the characteristic property of the helical kink instability of a twisted magnetic ?ux rope.The instability occurs if the twist,a measure of the winding of the ?eld lines about the ?ux rope axis,exceeds a critical value (Hood &Priest 1981).

In coronal applications,the simplifying assumption of straight,cylindrically symmetric ?ux ropes has nearly always been used so far.Only very recently,T?r?k,Kliem,&Titov (2004,hereafter Paper I)performed the ?rst detailed study of the kink instability of an arched ?ux rope,line-tied to the photosphere,using the analytical model of a force-free coro-nal ?ux rope developed by Titov &Démoulin (1999,hereafter TD)as the initial condition in 3D ideal MHD simulations.They have shown that this model relaxes to a numerical equi-librium very close to the analytical expressions in the case of subcritical twist and that the helical kink instability develops for supercritical twist (see also Fan &Gibson 2003,2004).

1

Mullard Space Science Laboratory,University College London,Holm-bury St.Mary,Dorking,Surrey RH56NT,UK;tt@https://www.wendangku.net/doc/e77019305.html, 2Astrophysical Institute Potsdam,An der Sternwarte 16,14482Potsdam,Germany;bkliem@aip.de

In the course of the instability,a helical current sheet,wrapped around the kinking and rising ?ux rope where it pushes into the surrounding ?eld,and a vertical current sheet below the rope (which has no counterpart in the cylindrically symmetric case)are formed.A vertical current sheet below rising unstable magnetic ?ux is the central element in the stan-dard model of eruptive solar ?ares.Further essential features of solar eruptions could be reproduced in the simulations,as for example the formation of transient soft X-ray sigmoids (Kliem,Titov,&T?r?k 2004,Paper II).However,a full erup-tion of the con?guration has not yet been obtained;the ?ux rope reached an elevation of only about twice its initial height.Here we present further developments of these simulations to substantiate our suggestion in Papers I and II that the kink instability of a coronal magnetic ?ux rope is a possible trig-ger mechanism of solar eruptions.The instability was ?rst suggested as the trigger of (con?ned and ejective)prominence eruptions by Sakurai (1976),but has recently been generally regarded as a possible explanation only for con?ned events (e.g.,Gerrard &Hood 2003).The new simulations show that the instability can also trigger full eruptions.

2.NUMERICAL MODEL

We integrate the compressible ideal MHD equations using the simplifying assumptions of vanishing plasma-beta,β=0,and vanishing gravity,which are identical to Eqs.(2–5)in Pa-per I.Setting β=0is usually a very good approximation in the lower and middle corona of active regions,the source region of most eruptions,where estimates yield β～10?3...10?2.Both the pressure gradient force and the gravity force in?u-ence the rise characteristics of the unstable ?ux rope and the energy partition in the development of the instability.How-ever,the basic characteristics of the instability are well de-scribed by the equations used whenever the Lorentz force dominates,as is the case in the initial phase of solar erup-tions.Magnetic reconnection occurs in the simulations due to numerical diffusion if current sheets steepen suf?ciently.As in Papers I and II,we use the approximate analytical force-free equilibrium of an arched,line-tied,and twisted ?ux rope by TD as the initial condition for the magnetic ?eld.The ?ux rope is modelled by the upper section of a toroidal

2T?r?k&

Kliem

F IG.1.—Left:TRACE195?images of the con?ned?lament eruption on2002May27.Right:magnetic?eld lines outlining the core of the kink-unstable?ux rope(with start points in the bottom plane at circles of radius b/3)at t=0,24,and37.The central part of the box(a volume of size43)is shown,and the magnetogram,B z(x,y,0,t),is included.

ring current,partly submerged below the photosphere,whose Lorentz self-force is balanced by a pair of?ctitious subpho-tospheric magnetic charges.A?ctitious subphotospheric line current at the toroidal symmetry axis is included to achieve a ?nite twist everywhere in the system.See TD for a detailed description of the model.

The initial density distribution can be freely speci?ed;we choose it such that the Alfvén velocity in the volume sur-rounding the?ux rope decreases slowly with height:ρ0∝|B0(x)|3/2(see Fig.3below).The system is at rest at t=0, except for a small upward velocity perturbation,which is lo-calized at the?ux rope apex in a sphere of radius equal to the minor radius,b,of the rope.Lengths,velocities,and times are normalized,respectively,by the initial?ux rope apex height, h0,the initial Alfvén velocity at the apex,v A0,and the corre-sponding Alfvén time,τA=h0/v A0.

3.SIMULATION OF A CONFINED ERUPTION

The eruption of an active region?lament(on2002May27), which was accompanied by an M2?are but did not lead to a CME,was described by Ji et al.(2003).The?lament started to rise rapidly and developed a clear helical shape,as is often observed;however,the ascent was terminated at a projected height of≈80Mm(Figs.1,2).Such con?ned?lament erup-tions are not uncommon(Rust2003).

1

2

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4

2

4

6

8 h

(

t

)

h

[

1

4

k

m

]

010********

t [τ

A

]

0.0

0.1

1

2

3 u

(

t

)

u

[

1

2

k

m

s

-

1

]

18:0118:0318:0518:0718:09UT

F IG.2.—Comparison of height,h(t),and velocity,u(t),of the?ux rope apex in the simulation(solid lines;initial perturbation is dotted)with the corresponding values of the?lament eruption in Fig.1(data from Fig.3 of Ji et al.[2003])overplotted as diamonds(the height data observed before 18:04UT were smoothed here,resulting in reduced velocity scatter).See text and Table1for the scaling of the dimensionless simulation variables (left axes)to the observed values(right axes).

In order to model this event,we consider a kink-unstable con?guration which is very similar to the case of an average ?ux rope twist of4.9πstudied in detail in Paper I.The line current is reduced by about one third to enable a higher rise, but the average twist,Φ=5.0πhere,is kept to reproduce the helical shape.(In the TD model,this?xes the minor radius to b=0.29,8percent larger than in the reference run in Pa-per I.)The sign of the line current is chosen to be positive to conform to the apparent positive(right-handed)helicity of the observed?lament.Furthermore,we increase the numeri-cal diffusion and prevent the density from becoming negative, which permits us to follow the evolution of the system for a considerably longer time.Otherwise,the magnetic con?gura-tion and the numerical settings are the same as in Paper I.

As in our previous simulations,the upwardly directed kink instability leads to the ascent and helical deformation of the ?ux rope as well as to the formation of current sheets(see Fig.3in Paper I).In Fig.1we compare the evolution of the he-lical shape of the?ux rope with Transition Region and Coro-nal Explorer(TRACE)observations of the?lament eruption. The evolution is remarkably similar.Figure2shows that the principal features of the observed rise are also matched.After an exponential rise the?ux rope comes to a stop at≈3.5h0. A?rst deceleration occurs as the current density in the heli-cal current sheet above the apex begins to exceed the current density in the?ux rope(t>22).The subsequent upward push (t>30)results from the reconnection out?ow in the vertical current sheet below the rope.Finally,the rise is terminated by the onset of magnetic reconnection in the current sheet above the rope,which progressively cuts the rope?eld lines(t 33). The reconnection out?ows expand the top part of the rope in lateral direction,as seen both in observation and simulation. Using the scaling to dimensional values given in Table1, good quantitative agreement with the rise pro?le is obtained (Fig.2),and the release of magnetic energy in this run of 5percent corresponds to1031erg,a reasonable value for a con?ned M2-class?are.

The agreement between the observations of the event and our simulation con?rms the long-held conjectures that the de-velopment of strongly helical axis shapes in the course of eruptions can be regarded as an indication of the kink instabil-

Eruptions of kink-unstable?ux ropes3

TABLE1

P ARAMETER S ETTINGS

Simulation Parameters Scaling Parameters

Sect.Φ/πbη(2)L h0τA|B0(h0)|W

(Mm)(s)(G)(erg)

35.00.290.83102311.52001031

4?5.00.33 1.543211511110-401031–32

N OTE.—The expressionη(z)=?z d ln B ex(0,0,z,0)/dz is the‘decay in-

dex’of the‘external’?eld(excluding the contribution by the ring current),L is the box size,and W is the released magnetic energy.The runs are equal in grid resolution in the central part of the box,?=0.02,major rope ra-dius,R=1.83,and distance of the?ctitious magnetic charges from the z axis, l=0.83.

ity of a twisted?ux rope and that the frequently observed heli-cal?ne structures in erupting?laments and prominences out-line twisted?elds.Furthermore,it shows that?ux ropes with substantial twist can exist or be formed in the solar corona at the onset of,or prior to,eruptions.

4.SIMULATION OF AN EJECTIVE ERUPTION(CME)

The full eruption of the kink-unstable?ux rope in the TD model is prevented by the strong overlying?eld,which is dominated by the line current.It is possible to obtain an erup-tive behaviour of the?ux rope by removing the line current; however,such a modi?cation leads to an in?nite number of ?eld line turns at the surface of the?ux rope(Roussev et al. 2003).In order to avoid this problem,we replaced the line current by a pair of subphotospheric dipoles(as used in T?r?k&Kliem2003).The position of the dipoles is chosen such that the?eld lines of the dipole pair passing through the ?ux rope match the curvature of the rope as closely as possi-ble.The resulting equilibrium yields a?nite twist everywhere in the system,but the magnetic?eld overlying the?ux rope now decreases signi?cantly faster with height than in the orig-inal TD model(Fig.3).By varying the dipole moments or the minor radius b,one can adjust the average twist within the ?ux rope.

Choosing suitable dipole moments and b=0.6,but oth-erwise the same parameters of the TD model as in Sect.3, we?rst checked that the modi?ed con?guration relaxes to a nearby stable equilibrium for subcritical twist,Φ=2.7π.Next a con?guration with supercricital twist,Φ=?5.0π,is consid-ered,obtained by changing the minor radius to b=0.33and reversing the dipole moments.The sign of the helicity corre-sponds to the2001May15event discussed below;it has no in?uence on the rise,h(t),of the?ux rope apex.The numer-ical parameters of the simulation are the same as in Sect.3, except for a considerably larger simulation box and a smaller level of numerical diffusion,which this system permitted. The helical kink instability also develops in the modi?ed model.However,the?ux rope now exhibits a much stronger expansion(Fig.4),which is not slowed down.The initially exponential rise is followed by a rise with approximately con-stant and locally super-Alfvénic velocity,until the rope en-counters the top of the simulation box(at t≈80).The helical current sheet remains very weak on top of the?ux rope apex and no signi?cant amount of reconnection occurs here.On the other hand,the vertical current sheet now steepens in a large height range.Magnetic reconnection commences in this sheet at the beginning of the exponential phase and rises in tandem with the ascent of the?ux rope,particularly closely during the

051015

z

0.001

0.010

0.100

1.000

B

,

v

A

F IG.3.—Normalized initial magnetic?eld strength(thick lines)and Alfvén velocity(thin lines)vs.height for the con?gurations described in Sect.3 (original TD model;dashed lines)and Sect.4(modi?ed TD model;solid lines).

exponential phase.Since the?ux rope expands continuously during this phase(instead of being compressed by the upward reconnection out?ow below it)and moves away from the fore-front of the out?ow region afterwards,the ideal instability of the?ux rope appears to be the driver of the closely coupled processes.Cusp-shaped?eld lines are formed throughout the evolution(Fig.4)but most prominently in the late phase,in agreement with soft X-ray observations of eruptive?ares. The full eruption of the?ux rope in the modi?ed TD model must be enabled by the weaker overlying?eld,since all other parameters are identical,or very close,to Sect.3.

In Fig.5we compare the rise of the?ux rope apex in the simulation with the rise of the apex of a well observed erup-tive prominence on2001May15,which occurred in a spot-less region slightly behind the limb and led to a fast CME (peak velocity of leading edge≈1200km s?1)and a long-duration?are(X-ray class C4).As described by Mariˇc i′c et al. (2004),the eruptive prominence developed a helical shape, analogous to the middle panels in Fig.1with reversed hand-edness,and it showed the typical rise characteristics of a fast CME(initially exponential or exponential-like rise,followed by approximately linear rise;Vr?nak2001).For this com-parison,we?rst scaled the Alfvén time such that the dura-tion of the exponential rise phase is matched,τA=111s, and shifted the time axis accordingly.Then we scaled the length unit such that the apex height at the point of peak acceleration in the simulation(t=21)equals the height of the prominence at the resulting observation time(see bottom axis),i.e.,h0=115Mm.This?xes the scaling of the velocity and acceleration amplitudes.Apart from a somewhat more gradual decrease of the observed acceleration after the peak, excellent qualitative and quantitative agreement is obtained, demonstrating(as in Sect.3)that the kink instability yields the growth rate required by the observed rise pro?le for the twist indicated by the observed helical shape.The slight dif-ference in the late acceleration pro?le may have many origins, for example,a different height pro?le of the?eld strength,or a simultaneous expansion of the overlying?eld enforced by photospheric?ows in the observed event.

The simulation shows a strong magnetic energy release, 25percent of the initial value,which agrees with the mag-nitude observed in ejective solar eruptions(Forbes2000; Emslie et al.2004).The considered event may have released magnetic energy of order～(1031–1032)erg(the low X-ray class resulted from footpoint occultation).Using the above scaling for h0,this energy release is reproduced for B0～

4T?r?k &

Kliem

F I

G .4.—Magnetic ?eld lines of the kink-unstable modi?ed TD model at t =0(left ),t =30(center ),and t =43(right ).The magnetogram,B z (x ,y ,0,t ),is included.Field lines started at a circle of radius b /3in the bottom plane show the core of the ?ux rope.Additional green ?eld lines,also with identical start points in all panels,indicate the formation of “post ?are loops”with a cusp by reconnection.The hyperbolic point of the ?eld at the z -axis (magnetic X-point)lies at z ≈0.2,0.6,and 1.1,respectively.

1.0010.0h (t )

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h [R S u n ]

0.010.101.00u (t )

101 102

103 u [k m s -1]

01020

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G .5.—Comparison of the simulation in Sect.4with the CME on 2001May 15in the same format as in Fig.2,including the acceleration a (t ).Dia-monds show the apex motion of the erupting prominence/the CME core (data are from Fig.6a,c of Mariˇc i′c et al.[2004]).

(10–40)G,consistent with expected averages of the coronal ?eld strength over the large length scales involved.

The simulation could also be scaled to a ?lament eruption that was associated with an X-class ?are and a very fast CME (on 2004November 10;see Williams et al.2005).

A line-tied ?ux rope was found to erupt in a few previous simulations (Amari et al.2000,2003a,b).The present simu-lations,through their agreement with characteristic properties

of solar eruptions,identify a mechanism for the process,con-?rming the original suggestion by Sakurai (1976).They also demonstrate the importance of the height dependence of the overlying ?eld for the evolution of the instability into a CME,while Amari et al.(2003b)found the amount of magnetic he-licity to be essential.Since Amari et al.built up the helicity by rotating the main photospheric polarities,which simulta-neously expands the overlying ?eld (T?r?k &Kliem 2003),both results are fully consistent with each other.

5.CONCLUSIONS

Our MHD simulations of the kink instability of a coronal

magnetic ?ux rope reproduce essential properties—an ini-tially exponential rise with the rapid development of a heli-cal shape—of two well observed solar eruptions,one of them con?ned,the other ejective.The subsequent approximately linear rise of the ejective eruption is reproduced as well.Since these features are characteristic properties of many solar erup-tions (Vr?nak 2001),we regard the kink instability of coronal magnetic ?ux ropes as the initiation mechanism and initial driver of many such events.A suf?ciently steep decrease of the magnetic ?eld with height above the ?ux rope permits the process to evolve into a CME.

We acknowledge constructive comments by the referee and thank H.Ji and B.Vr?nak for the observation data in Figs.2and 5,respectively.This work was supported by grants 50OC 9706(DLR),MA 1376/16-2(DFG),and HPRN-CT-2000-00153(EU).The John von Neumann Institute for Com-puting,Jülich granted computer time.

REFERENCES

Amari,T.,et al.2003a,ApJ,585,1073Amari,T.,et al.2003b,ApJ,595,1231

Amari,T.,Luciani,J.F.,Mikic,Z.,&Linker,J.2000,ApJ,529,L49Emslie,A.G.,et al.2004,J.Geophys.Res.,109,A10104Fan,Y .,&Gibson,S.E.2003,ApJ,589,L105Fan,Y .,&Gibson,S.E.2004,ApJ,609,1123Forbes,T.G.2000,J.Geophys.Res.,105,23153

Gerrard,C.L.,&Hood,A.W.2003,Sol.Phys.,214,151

Hood,A.W.,&Priest,E.R.1981,Geophys.Astrophys.Fluid Dyn.,17,297Ji,H.,et al.2003,ApJ,595,L135

Kliem,B.,Titov,V .S.,&T?r?k,T.2004,A&A,413,L23(Paper II)Mariˇc i′c ,D.,Vr?nak,B.,Stanger,A.L.,&Veronig,A.2004,Sol.Phys.,225,337

Roussev,I.I.,et al.2003,ApJ,588,L45Rust,D.M.2003,Adv.Space Res.,32,1895Sakurai,T.1976,PASJ,28,177Shibata,K.1999,Ap&SS,264,129

Titov,V .S.,&Démoulin,P.1999,A&A,351,707(TD)T?r?k,T.,&Kliem,B.2003,A&A,406,1043

T?r?k,T.,Kliem,B.,&Titov V .S.2004,A&A,413,L27(Paper I)

Eruptions of kink-unstable?ux ropes5 Vr?nak,B.2001,J.Geophys.Res.,106,25249

Williams,D.R.,T?r?k,T.,Démoulin,P.,van Driel-Gesztelyi,L.,&Kliem,

B.2005,ApJ,628,L163

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