J. Büchner+collaborators, at different times, were:
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Transcript of J. Büchner+collaborators, at different times, were:
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Consequences of LHDI for three-dimensional collisionless reconnection through thin current sheets
J. Büchner+collaborators, at different times, J. Büchner+collaborators, at different times, were: were:
J. Kuska, B. Nikutowski, I.Silin, Th.Wiegelmann J. Kuska, B. Nikutowski, I.Silin, Th.Wiegelmann
all at: Max-Planck Institut für Sonnensystem-all at: Max-Planck Institut für Sonnensystem-forschung in Katlenburg-Lindau, Germany forschung in Katlenburg-Lindau, Germany
(for „Solar System Research“ starting 1.7.2004 (for „Solar System Research“ starting 1.7.2004 after being „for Aeronomy“ the last 40 years)after being „for Aeronomy“ the last 40 years)
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Topics• Gradient and current-driven plasma instabilities in
current sheets • Initiation of 3D collisionless reconnection (PIC->Vlasov-
simulation approach) in / through– anti-parallel magnetic fields– creation / annihilation of helicity density– non-anti-parallel, finite guide magnetic field case– asymmetric (magnetopause) current sheet case
• „Anomalous resistivity“ approach to introduce kinetic results into large scale MHD
• EUV Bright Points (BP): MHD modeling of the dynamic evolution (photospheric flows) + anomalous transport=> Null point <or> finite B <or> QSL reconnection ???
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
3D current sheet instabilities• 1970th: quasi/linear theory: LHD-instability at the edges
(Drake, Huba, Davidson, Winske, Tanaka & Sato ... )• 1996: 3D PIC simulations showed: global (kink/sausage)
mode current sheet instabilities can initiate reconnection
(Pritchett et al.; Zhu & Winglee; Büchner & Kuska 1996)• 1998...now: New theory - and simulation results about
current-driven and drift instabilities at sheet center
(Horiuchi & Sato; Büchner, Kuska & Silin; Daughton et al.)• Our latest move:
From PIC to Vlasov-codes to test wave-particle
interactions, resonances etc. which can initiate
current sheet instabilities and reconnection
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Vlasov equation: 0)(1
v
fBv
cE
m
e
r
fv
t
f j
j
jjj
Linear perturbation of distribution functions
tdv
fBvEc
cm
etf
tj
j
jj
0111 )(
Resulting perturbation of density and current
vdfvej
vdfe
jjj
jjj
11
11
Maxwell equations for the fields or wave equation for the potentials
121
2
21
121
2
21
41
41
jct
A
cA
tc
Kinetic stability investigation
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
-> > 20o: Eigenmodes are linearily stable(k=k0 cos ex +k0 sin ey)
Linear stability of oblique eigenmodes at current sheet center
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Vlasov simulation code
vdfvej
vdfe
ei
Veijei
V
eieij
ei
3,
,,
3,
,,
121
2
21
121
2
21
41
41
jct
A
cA
tc
0)(1 ,
,
,,,
v
fBv
cE
m
e
r
fv
t
f ei
ei
eieiei
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Nonlinear LHDI (anti-parallel fields: Vlasov kinetic simulation)
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Non-local penetration of LHD unstable waves
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Simulation shows: the Ey fluctuations grow also at the center
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Drift-resonance instability (DRI)
1D ion distribution in the current direction
1D electron distribution in the current direction
Ions drive waves → plateau-formation → electron-heating
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
DRI: 3D distribution function
3D Ion distribution function 3D electron distribution
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
3D current sheet instability
(Plasma density perturbation; case of antiparallel fields) (Plasma density perturbation; case of antiparallel fields)
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Current sheet thickness C1<->C4 (7.9.01, 19:00>23:00)
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Current sheet waves ~21:00 UT
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Current sheet waves –observed by Cluster as predicted
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Waves initiate 3D reconnection
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Mechanism:Wave- reconnection coupling:
Dashed: LHDI (edge) ; Solid: LHDI at the center; Dashed-dotted: reconnecting mode
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
3D reconnection island:
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
2.) Helicity density evolution:a.) 3D antiparallel
reconnection
0 const. B)d (A H 3M x
Spheres: quadrants 1 and 4
Squares: quadrants 2 and 3
Solid line - total helicity:
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Antiparallel -> finite guide field By
guide field By -> flux ropesguide field By -> flux ropesQuadrupolar By fieldQuadrupolar By field
-> Bending of B-fields-> Bending of B-fields
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Finite guide field case -> non 180o magnetic shear Guide fields change the shear angle between the ambient B-fields
1 8 0 °
M S P M S HJ
1 2 5 °
M S P M S H
J
2 1 0 °
M S P M S HJ
180o
(J = direction of sheet current and of reconnection E- field)
Negative Co-
helicity HMo < 0
Positive Co-helicity
HMo > 0 0 B)d (A H 3Mo x
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
3D guide field reconnection: initially positive co-helicity case
oi t = 1 oi t = 25
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
2D / 3D positive co-helicity reconnection („pull reconnection“)
Dotted: quadrants 1 and 4
Dashed: quadrants 2 and 3
Solid line - total helicity:
0d B) (E2- H 3M
xdt
d
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
oi t = 1
oi t = 23
3D guide field reconnection: initially negative co-helicity case
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
2D / 3D negative co-helicity reconnection („push reconnection“)
Dotted: quadrants 1 and 4
Dashed: quadrants 2 and 3
Solid line - total helicity:
0d B) (E2- H 3M
xdt
d
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
3.) Resonant DRI in the guide field case:
The growth rate of the instability decreases proportionally to the number of resonant ions.
For stronger guide fields the cross-field
propagation direction turns
further away from the current direction.
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Reconnection wave in a non- anti-parallel (guide field) current sheet
Bz in linear presentation for the polarity of magnetic bubbles
Bz in log presentation turbulence -> structure
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Result: patchy reconnection in the
non-anti-parallel, guide field case:
The B field opens the boundary throug local patches (blue: below, red: above)
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Simulation model
The pressure being locally balanced; drift Maxwellians,
drifts
currents
4: Non-symmetric case (MP)
-> fields rotate through a tangential magnetic boundary
Bc
j
4
eiei TTuu //
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Instability of a non-symmetric magnetic boundary current sheet
LHD instability first on magnetospheric side (z<0) -> penetrates to the magnetosheath side (z>0) and triggers reconnection - island formation
Magnetic
field Bz:
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Magnetopause observation (Cluster)
A. Vaivadset al., 2004
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
5.) Quasilinear estimate of the WP momentum exchange (-> “anomalous collision frequency;-> “... resistivity”)
(Davidson and Gladd, Phys. Fluids, 1975)
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Anomalous momentum exchangedue to nonlinear DRI in a current sheet:
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
6.) X-ray & EUV Bright Points (BPs): quiet-sun reconnection
- XBP are formed inside diffuse clouds, which grow at 1 km/s up to 20 Mm and then form a bright core 3 Mm wide, they last, typically, 8 h
Vaiana, 1970: rockets; Golub et al. 1974-77: Skylab More recently: SOHO and TRACE observations
-Later (Soho...) : also many EUV BP investigated
-> BP are assumed to be prime candidates for reconnection: they well correlate with separated photospheric dipolar (opposite polarity) photospheric magnetic fluxes
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Soho-MDI and EIT: EUV BP
MDI line-of sight magnetic
field
( 40” x 40”)
EIT (195 A) same field of
view
17-18.10.1996 (M. Madjarska et al., 2003)
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Reconnection models for BP
- Due to the B separation in the photosphere -> Reconnection between bipoles
assumed to take place in the corona, -> magnetohydrostatic models, e.g.
- Newly Emerging Flux Model (EMF) Heyvaerts, Priest & Rust 1977
- Converging flux model Priest, Parnell, Martin & Gollup, 1994- Separator Reconnection in MCC
Longcope, 1998
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
But: dynamical footpoint motion:
-> currents are driven into the chromosphere/corona
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Model, starting with extrapolated B-fields ...
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
... and footpoint motion (here after 1:39 ...and density-heightUT 18.10.96): profile (VAL):
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Density Evolution -> t=128
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Parallel electric fields and parallel currents at t=128
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Transition region parallel electric fields
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Transition region reconnection
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Reconnection due to resistivity switched on enhanced current (velocity)
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Not at a null, but between two nulls (separator through 35,20,5 ?)
<- Iso-surfaces of a smalltotal magnetic field, henceembedding the nulls
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Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004
Further work planned on:• Current sheet instabilities for more
realistic current and field models and their consequences for reconnection
• resulting anomalous transport as an approach toward quantifying the coupling between MHD and kinetic scales for solar and magnetospheric applications
• Reconnection at neutral points vs. separator reconnection vs. quasi-separatrix layer - reconnection in the course of the dynamically evolving „magnetic carpet“ („tectonics“)