Transcript Solar Flares and Magnetic Reconnection

Solar-B science meeting
2003.2.3-5. ISAS, NAOJ
Solar Flares and
Magnetic Reconnection
T. Yokoyama (NAOJ)
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Introduction
• Present status of our understanding
(observation, theory)
• Open questions on magnetic
reconnection theory
• (What to be observed)
• Warning : very biased !
Carmichael (1964); Sturrock (1966);
Hirayama (1974); Kopp & Pneuman (1976)
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Present status of our understanding
— observation
• Observational pieces of evidence
– Cusps (Tsuneta et al. 1992)
– Above-the-loop HXR source (Masuda et al.
1994)
– Outflow/ejection (McKenzie & Hudson
1999; Ohyama & Shibata 1997)
– Inflow (Yokoyama et al. 2000)
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Observational evidence for the
magnetic reconnection model
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Detection of reconnection inflow
Yohkoh/SXT
SOHO/EIT
Yokoyama et al. (2000)
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Detection of reconnection inflow
Vinflow  4.7km/s
Vinflow / CA  0.001 0.03
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Present status of our understanding
— observation
• Observational pieces of evidence
– Cusps (Tsuneta et al. 1992)
– Above-the-loop HXR source (Masuda et al.
1994)
– Outflow/ejection (McKenzie & Hudson
1999; Ohyama & Shibata 1997)
– Inflow (Yokoyama et al. 2000)
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Present status of our understanding
— theory
• “Realistic” simulations (e.g. Yokoyama &
Shibata 2001)
• What is the condition for the fast
reconnection ?
– The localized resistivity is necessary (Ugai
1992; Kulsrud 2001).
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“Realistic” simulation of a flare
Yokoyama & Shibata (2001)
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Present status of our understanding
— theory
• “Realistic” simulations (e.g. Yokoyama &
Shibata 2001)
• What is the condition for the fast
reconnection ?
– The localized resistivity is necessary (Ugai
1992; Kulsrud 2001).
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Localized resistivity for the necessary
condition of fast reconnection
Yokoyama & Shibata (1994)
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Present status of our understanding
— theory
• “Realistic” simulations (e.g. Yokoyama &
Shibata 2001)
• What is the condition for the fast
reconnection ?
– The localized resistivity is necessary (Ugai
1992; Kulsrud 2001).
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Open questions on magnetic
reconnection
• Local enhancement of magnetic
diffusion
– Had been a conjecture (Coppi & Friedland
1971)
– Finding in laboratory plasma (Ono et al.
2001; Ji et al. 2001)
• Scale-matching between the macro and
the micro
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Enhancement of resistivity in the
laboratory plasma
• Ono et al. (2001)
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Open questions on magnetic
reconnection
• Local enhancement of magnetic
diffusion
– Had been a conjecture (Coppi & Friedland
1971)
– Finding in laboratory plasma (Ono et al.
2001; Ji et al. 2001)
• Scale-matching between the macro and
the micro
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Enormous gap of scale sizes
• Scale-size of
the anomalous resistivity
d = ri ~ 10 m
d ; Thickness of the current sheet
ri ; Ion Larmor radius
• Scale size of a flare: 104 km !
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Fractal current sheet
• Tajima & Shibata (1997)
~1 km
~104 km
~10 m
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Turbulence ? in outflow
• Tanuma & Shibata (2003)
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Turbulent reconnection
• Lazarian & Vishniac (1999)
Vin  CA M
2
turb
M turb
: large-scale magnetic
Mach number of the
turbulence
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MHD simulations of turbulent
reconnection
• Yokoyama (2003): very preliminary !
4
Without turbulence
pressure
Y=0
-4-32
X=0
32
With turbulence
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MHD simulations of turbulent
reconnection
• Yokoyama (2003): very preliminary !
Vptb  0.75CA
Vptb  0
dEmag
dt
Time
Emag
Time
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Summary
• We have many observational pieces of
evidence which support the reconnection
model of solar flares.
• The localized resistivity is necessary for
magnetic reconnection, and is now found in
the laboratory plasma in the micro-scale.
• But there is still an enormous gap between
the micro-scale of the anomalous resistivity
and the size of a solar flare.
• The scale matching problem is very important.
The MHD turbulence may be a key process.
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