magnetic reconnection in flares yokoyama, t. (naoj) reconnection mini-workshop 2002.7.9. kwasan obs....
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Magnetic Reconnection in Flares
Yokoyama, T. (NAOJ)
Reconnection mini-workshop 2002.7.9. Kwasan obs.
Main Title
1. Introduction : Reconnection Model of a Flare
2. Direct Observation of a Reconnection Inflow
3. MHD Simulation of a Flare
Reconnection Model of a Flare
& Yohkoh Observations
Observation of solar flares by Yohkoh
• Cusp-shape of the flare loop (Tsuneta et al. 1992)• Loop-top hard X-ray source (Masuda et al. 1994)
• Plasma ejection associated with a flare
Shibata et al. (1995); Ohyama et al. (1997)
Magnetic reconnection model of solar flares
Carmichael (1964); Sturrock (1966); Hirayama (1974); Kopp & Pneuman (1976)
Magnetic energy of coronal field
Magnetic reconnection
Bulk kinetic & thermal energy of
plasma
Observation of
Reconnection Inflow in a Flare
T. Yokoyama (NAOJ)
K. Akita (Osaka Gakuin Univ.)T. Morimoto, K. Inoue (Kyoto Univ.)
J. Newmark (NASA/GSFC)
Many pieces of indirect evidence
cusp loops, loop-top HXR sources, plasma ejection
supporting MHD simulations
FOUND !!
But … for solar flares, here has been
NO direct evidence of reconnection
NO observation of energy-release site itself
We should search for the reconnection flows …
2. Flare 1999-3-18
• Long-Duration Event (LDE; ~300A) on the NE solar limb• Simultaneous coronal mass ejection (CME)
SOHO/EIT SOHO/LASCO
Soft X-ray Observation by SXT of Yohkoh
• cusp-shaped flare loops
100,000 km
3:03 3:22 4:37
8:03 16:27 0:31
T > 4MK
Observation of plasmoid ejection and reconnection inflow
EUV~1.5MK
SXR> 4MK
100,000 km
Observation of plasmoid ejection and reconnection inflow
Observation of plasmoid ejection and reconnection inflow
Plasmoid ejection
Inflow
Reconnected loop
X-point
Evolution of 1D plot of EIT data across the X-point
Evolution of 1D plot of SXT data along the cusp
Energy release rate
(1)
Derivation of reconnection rate
• From SXR observation
Lifetime
• From EUV observation
Energy release rate (2)
From (1) = (2)
Thus, we obtain
Consistent with the Petschek model.
MHD Simulation of
a Flare
T. Yokoyama (NAOJ)K. Shibata (Kyoto Univ.)
MHD Simulation of a Flare Yokoyama & Shibata (1998)
• Simulation from the peak to the end of the decay phase
• Growth and cooling of post-flare loops
• Light curve, differential emission measure
In this study
Heat Conduction, Evaporation & Radiation Cooling
This Study
Numerical Model• 2.5-dimensional MHD
• Non-linear non-isotropic (Spitzer type) heat conduction
• Cooling by the optically-thin radiation
• No gravity
• Initially in magnetohydrostaticequilibrium
• Localized resistivity
• For typical case, Plasma = 0.2Alfv = 100 sec cond = 600 sec rad = 16000 sec
Numerical Model chromosphere
corona
Time Series
Temporal Evolution
Movie : Temperature
Movie : Temperature
Movie : Density
Movie : Density
Effects of the Heat Conduction & Radiation Cooling
Only MHD
Temperature
Density
Effects of Heat Conduction & Radiation Cooling #0
Effects of the Heat Conduction & Radiation Cooling
Temperature
Density
Only MHDConduction
Effects of Heat Conduction & Radiation Cooling #1
Conduction & Radiation
Conduction
Effects of the Heat Conduction & Radiation Cooling
Temperature
Density
Only MHD
Effects of Heat Conduction & Radiation Cooling #2
This is the case without the radiation but with the conduction.
Differential Emission Measure (DEM) Derived from the Simulation Results
Time
Time
DEM
• Rapid increase of the DEM of hot plasma in the rise phase, keeping the temperature.
• Temperature of maximum DEM decreases in the decay phase, keeping the amount of the DEM.
TimeDere & Cook (1979)
( only initial part of the decay phase )
DEM Derived from the Simulation
DEM Derived from the Observations
DEM: Comparison
Light Curve & Energy Budget
• The energy release continues even in the decay phase.
• The total amount of the released (magnetic) energy is several times the thermal energy derived from the snap shot at the peak of the flare.
Light Curve & Energy Budget
Parameter survey : Effect of plasma
• When the is smaller, the cooling time is shorter. 5.0 Plasma Beta #0
• When the is smaller, the cooling time is shorter.
5.0
57.07/4
• Explanation
If we assume is independent of at the start of the radiation cooling process
T
Plasma Beta #1
nT /rad radiation:
7/47/8 Bnenergy balance in reconnection &
magnetic confinement
(Shibata & Yokoyama 1999)
Summary
• Many pieces of evidence supporting the magnetic reconnection model of flares were found by recent space-craft observations.
• There is one example of direct observation of reconnection inflow.
• We developed a 2.5-dimensional MHD code including the effects of heat conduction, chromospheric evaporation, and radiation cooling. It is applied to simulate a solar flare.
Summary
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