Solar Atmosphere as a Laboratory for Magnetic Reconnection

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Solar Atmosphere as a Laboratory for Magnetic
Reconnection

• Shinsuke Imada
• (ISAS/JAXA)

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Magnetic Reconnection
Inflow velocity
Current sheet thickness
Ion-Electron Heating Non-thermal acceleration
Outflow velocity Turbulence/wave
Slow shock
Magnetic field Density
Original idea is converting magnetic field
energy to plasma kinetic energy. Recently plasma
heating, particle acceleration and wave
excitation are also well discussed in the
category of magnetic reconnection. These energy
conversion rates are heavily depending on the
plasma conditions. In that sense it is very
interesting to discuss magnetic reconnection in
various plasma conditions.
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Plasmas in universe
weak collision
collisionless
collisional
Comparative studies important
This figure shows the density and temperature
relationship in the Sun, Earth, Lab, and astro
plasmas. The magnetic reconnection is studied in
various conditions, from collisionless to
collisional regime.
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What plasma parameter controls?
What is the goal of magnetic reconnection study?
I already mentioned that the importance of
understanding of energy conversion. This figure
shows the illustration of the energy conversion
in two plasma conditions. In my opinion to answer
this puzzles and answer what plasma condition
controls the each energy conversion rates.
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Dynamic activities seen in the chromosphere
Many magnetic reconnection seem to be taken place
in chromosphere.
One of the most important findings by Hinode!
I want to mention one of the most important
findings by Hinode. Hinode observed very
dynamical chromospheric activity which may be
associated with magnetic reconnection. Thus now
chromosphere is also a target of magnetic
reconnection. Is magnetic reconnection the same
as coronal reconnection?
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Relative importance of diffusivities
Assumption typical magnetic field profile of a
vertical flux tube
Ambipolar/Hall ?ci/?in ?ci Ion-cyclotron
freq ?B ?in Ion-neutral collision freq ? n
by K.A.P. Singh
Chromosphere ambipolar gt Hall, resistivity
May be not.. Recently Isobe-san studied the
magnetic reconnection in chromosphere. He
discusses relative importance of magnetic
diffusivity between Hall and ambipolar
diffusivity in chromosphere, and found ambipolar
diffusion is important in chromosphere.
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Ohmic only
In the presence of B0 point
By
x
Ambipolar diffusion does not work where
B0 Current is concentrated near B0 gt
thinning of current sheet
This movie shows the current sheet development in
case of only ohmic diffusivity. The upper panel
shows the magnetic field variation in space, and
the bottom is current density. In the case of
only ohmic diffusivity, the current will be
diffusing.
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Ambipolar only
In the presence of B0 point
By
x
Ambipolar diffusion does not work where
B0 Current is concentrated near B0 gt
thinning of current sheet
On the other hand, in the case of ambipolar
diffusivity, the magnetic field gradient go
steeper and forms the this current sheet. This is
because the ambipolar diffusion cannot work
magnetic field is zero.
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2.5D simulation (still preliminary)
Ohmic diffusion only
OhmicAmbipolar
Thin current sheet created by ambipolar
diffusion Formation of islands gt bursty
reconnection
Isobe et al, in preparation
Thus very bursty/sporadic magnetic reconnection
can be taken place in chromosphere.
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Solar Flare
LDE event
Impulsive event
Tsuneta et al., 1996
Tsuneta et al., 1997
Lets move to coronal magnetic reconnection which
we have a large amount of knowledge. This is the
very famous observation of solar flares, one is
LDE and impulsive event. We can see many
structure of flare loops, but we cannot see
reconnection region itself in many event.
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Standard model for Solar Flare
We should observe this region! with spectroscopy
YohkohHinode We understand very well
Tsuneta et al., 1996
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What we need?

• Typical dynamical timescale of reconnection
  10(Mm)/1000(km/s) 10s
• To observe steady reconnection, we should take
  one image within 10 sec
• Another important point is understanding of
  Thermal Non-Equilibrium plasma, to understand
  rapid and strong plasma heating.

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Thermal Non-Equilibrium Plasma

• Non-Gaussian Distribution function ?
  Power-law distribution, beam plasma time
  scale for equilibrium is very short
  (kinetic regime or e-e or p-p collision)
• Different temperature in different species
  ? TpgtTe time scale for
  equilibrium is relatively long (e-p
  collision)
• Ionization non-equilibrium ? strong
  heating or flare time
  scale for equilibrium is relatively long

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Ion Temperature
Imada et al., APJL 2009
Recently Imada et al proposed a method for
estimating an ion temperature by using emission
lines from different atomic species. This method
do not assume Ionization equilibrium. This method
will apply to solar flare near future.
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Ionization Process
Fe13 Fe14 Fe15
Fe16 Fe17
FeXIV FeXV FeXVI
FeXVII FeXVIII
ionization
recombination
a collisional and dielectronic recombination
S collisional ionization
These process linearly depend on density
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Example of ionization calculation
109/cc 1MK Shock angle 85degree
T1MK at tlt0 T41MK tgt0
41MK 1200km/s outflow Without thermal conduction
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Example of ionization calculationin Steady
Reconnection model
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Example of ionization calculationin case of
N108/cc
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Emission measure
Post Flare loop
20 x 1 Mm
1011/cc 15MK Ionization EQ
BlackJet NEQ?Red Jet EQ?BluePost flare loop EQ
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Spatial resolution
The necessary spatial resolution is the
separation of each line peaks. 1arcsec
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Necessary for next generation Solar observation

• To observe the dynamics of magnetic reconnection,
  we need high throughput spectrometer (This is
  most important!)
• We need several emission lines to diagnose inside
  the reconnection region because of NIEQ (line
  ratio or filter ratio may not work)
• To diagnose electron temperature, it is important
  to observe continuum in X-ray range (photon
  counting in X-ray range is useful)

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• Spatial resolution needs 0.10.5 arcsec
• Dynamical range is also important to remove the
  effect of bright post flare loops (Occulter
  may be useful)
• If we can change the direction of slit, it is
  very useful!

We want to see this region!
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