Transcript The 3D picture of a flare

The 3D picture of a flare
Loukas Vlahos
Points for discussion
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When cartoons drive the analysis of the data and
the simulations….life becomes very complicated
Searching for truth in the “standard model”
The 3D picture of a flare and were the loop and
loop top meet
The multi scale phenomena in complex magnetic
topologies and solar flares
The limits of MHD and the beginning of a big
physics challenge
When cartoons drive the analysis
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In the recent solar flare literature it is hard to
distinguish the real data from the implied
interpretation. We have seen many examples in
the preceding presentations.
Let me discuss the monolithic cartoon in detail
Let me tell you from the start that I believe that
the Loop top sources are embedded in the
acceleration volume and their not
High Coronal X-ray Sources
Tearing Mode Instability?
23:13:40 UT
23:16:40 UT
Sui et al. 2005
The 2D simulations of a cartoon
Jets and shocks in the 2D picture
Solar flares: Global picture
2.5D MHD
26th GA IAU, JD01 “Cosmic Particle Acceleration”, Prague, August 16, 2006
X-ray loop-top source produced by electrons
accelerated in collapsing magnetic trap
Karlicky & Barta, ApJ 647, 1472
Karlicky & Barta, 26th GA IAU, JD01 (poster)
2.5D MHD
Test particles
(GC approx.
+ MC collisions)
26th GA IAU, JD01 “Cosmic Particle Acceleration”, Prague, August 16, 2006
Radiation from the cartoon
Geometry
The MHD incompressible equations are solved to study magnetic
reconnection in a current layer in slab geometry:
Periodic boundary conditions
along y and z directions
Dimensions of the domain:
-lx < x < lx, 0 < y < 2ly, 0 < z < 2lz
Description of the simulation
Incompressible, viscous, dimensionless MHD equations:
V
1 2
 ( V   ) V   P  (  B)  B   V
t
Rv
B
1 2
   ( V  B) 
 B
t
RM
B  0
V  0
B is the magnetic field, V the plasma velocity and P the
kinetic pressure.
RM and Rv are the magnetic and kinetic Reynolds
numbers.
Numerical results: B field lines and current at y=0
Three-dimensional structure of the electric field
Isosurfaces of the electric filed at different times
t=50
t=300
t=200
t=400
Time evolution of the electric field
Isosurfaces of the electric field from t=200 to t=400
E = 1.5x10-3
E = 1.7x10-2
E = 7x10-3
Distribution function of the electric field
P(E)
t=200
t=300
t=400
E
Kinetic energy distribution function of electrons
t=50 TA
T=400 TA
P(Ek)
Ek (keV)
Ek (keV)
Kinetic energy as a function of time
Ek (keV)
protons
electrons
t (s)
3D null point - test particles
• Numerically integrate
trajectories of
particles in em fields
representative of
reconnection
• Widely studied in 2D
(e.g. X-type neutral
line, current sheet),
but few 3D studies
• B=B0 (x,y,-2z)
• We consider the
spine reconnection
configuration
Priest and Titov (1996)
2D
3D
spine
S Dalla and PK Browning
Energy spectrum of particles
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Strong acceleration
Steady state after
few 1000s
Power law spectrum
f  E 0.92
over ≈ 200 – 106
eV
Number of particles and energetics of
the monolithic current sheet
Configuration with 4 magnetic polarities
Separatrices: 2 intersecting cupola
separator
Null
Null
e1 , e3 : positive charges
e2 , e4 : negative charges
I
II
Motion of the charges
=> Current sheet at separator
=> Reconnection (with E//)
=> Flux exchange between domains
III
IV
(Sweet 1969, Baum & Brathenal 1980,
Gorbachev & Somov 1988, Lau 1993 )
4 connectivity domains
Main properties
Skeleton :
Null points + spines + fans + separators
“summary of the magnetic topology”
(Molodenskii & Syrovatskii 1977, Priest et al. 1997,
Welsch & Longcope 1999, Longcope & Klapper 2002)
Classification of possible skeletons (with 3 & 4 magnetic charges)
(Beveridge et al. 2002, Pontin et al. 2003, 1980,
Gorbachev & Somov 1988, Lau 1993 )
Global bifurcations :
They modify the number of domains
- separator bifurcation (2 fans meet)
- spine-fan bifurcation (fan + spine meet)
(Gorbachev et al. 1988,
Brown & Priest 1999, Maclean et al. 2004)
Definition of Quasi-Separatrix Layers
Corona:
- low beta plasma
- vA~1000 kms-1
Field line mapping to the “boundary” :
Jacobi matrix :
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x  , y   x , y : x x  , y   , y x  , y  
x /x  x /y  
F  
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y /x  y /y  
Initial QSL definition : regions where
N  || F || 1
Better QSL definition : regions where
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Squashing degree
|| F ||2
Q
 1
Bn, / Bn,
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Photosphere & below:
- high inertia, high beta
- low velocities (~0.1 kms-1)
- line tying
Same value of Q at both feet of a field line :
Q  Q
( Démoulin et al. 1996 )
( Titov et al. 2002 )
Example of an eruption
quadrupolar reconnection (breakout)
4 ribbons
1:57 UT
reconnection behind the twisted flux rope
(with kink instability) 2 J-shaped ribbons
MDI
( Williams et al. 2005 )
2:04 UT
Brief summary
Discret photospheric field :
(Model with magnetic charges)
--> Photospheric null points
Separatrices
--> Skeleton
Separator
Generalisation to
continuous field distribution :
Quasi-Separatrix Layers
Hyperbolic Flux Tube
Indeed, a little bit more complex…..
More still to come….
A different type of flaring configuration
Arch Filament System
H (Pic du Midi)
QSL chromospheric footprint
~ H ribbons
Soft X-rays (SXT)
27 Oct. 1993
X-ray loops
( Schmieder, Aulanier et al. 1997 )
Formation of current layers at QSLs (1)
• Expected theoretically : - with almost any boundary motions
- with an internal instability
Using Euler potential representation: magnetic shear gradient across QSL
( Démoulin et al. 1997 )
Surface Q = constant ( = 100 )
Formation of
current layers
(Titov, Galsgaard & Neukirch. 2003 )
Example of boundary motions
The 3D picture of a flare
Assume that ant time neighboring field
lines are twisted more than θ the current
sheet becomes unstable and the resistivity
jumps up
 The E=-vxB+ηJ
 Distributed E-fields do the acceleration
and the tangled field lines do create local
trapping producing the anomalous
diffusion
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Eruption and stresses (Kliem et al)
Emerging Flux Current Sheet
Emerging flux Current Sheet
The multi scale phenomena in solar
flares
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The Big structure is due to magnetic field
extrapolation. This extrapolated field has build in
already magnetic filed anisotropies and small
scale CS providing part of the coronal heating
The numerous loops and arcades are now
stressed further from photospheric motions
Compact Loops form CS internally (see Galsgaard
picture) and some loops erupt forming even more
stresses magnetic topologies (see Amari picture)
Pre-impulsive phase activity and post impulsive
phase activity is an indication of these stresses
What causes the impulsive flare? The sudden
formation of a big structure and its cascade.
The multi scale phenomena in solar
flares
The ideal MHD predicted coronal
structures are long and filled with many
CS covering many scales.
 A few CS are becoming UCS due to
resistivity changes
 A typical Multi scale phenomenon
 Suggestion: “Loop-top” and foot points
are connected with acceleration source.
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A new big physics challenge
How can we build a multi code
environment where most structures are
predicted by Ideal MHD. From time to time
small scales appear were we depart from
MHD and move to kinetic physics
 Drive such a code from photosphere (fluid
motions and emerging flux)
 We are currently attempting to model this
using a CA type model, as prototype and
will follow by MHD/Kinetic models
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