Main Title Reconnection mini-workshop 2002.7.9. Kwasan obs. Magnetic Reconnection in Flares Yokoyama, T. (NAOJ) • Introduction : Reconnection Model of a Flare • Direct Observation of a Reconnection Inflow • 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 • NOdirect 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; ~300tA) on the NE solar limb • Simultaneous coronal mass ejection (CME) SOHO/LASCO SOHO/EIT
Soft X-ray Observation by SXT of Yohkoh • cusp-shaped flare loops T > 4MK 3:03 3:22 4:37 8:03 16:27 0:31 100,000 km
Observation of plasmoid ejection and reconnection inflow EUV ~1.5MK SXR > 4MK 100,000 km
Observation of plasmoid ejection and reconnection inflow Plasmoid ejection Inflow X-point Reconnected loop
Derivation of reconnection rate • From SXR observation • Lifetime • Energy release rate • (1) • 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 This Study Yokoyama & Shibata (1998) In this study Heat Conduction,Evaporation & Radiation Cooling • Simulation from the peak to the end of the decay phase • Growth and cooling of post-flare loops • Light curve, differential emission measure
Numerical Model Numerical Model Alfv = 100 sec cond = 600 sec rad = 16000 sec • 2.5-dimensional MHD • Non-linear non-isotropic (Spitzer type) heat conduction • Cooling by the optically-thin radiation • No gravity • Initially in magnetohydrostatic • equilibrium • Localized resistivity • For typical case, corona Plasma b = 0.2 chromosphere
Time Series Temporal Evolution
Movie : Temperature Movie : Temperature
Movie : Density Movie : Density
Effects of the Heat Conduction & Radiation Cooling Effects of Heat Conduction & Radiation Cooling #0 Only MHD Temperature Density
Effects of the Heat Conduction & Radiation Cooling Effects of Heat Conduction & Radiation Cooling #1 Conduction Only MHD Temperature Density
Effects of the Heat Conduction & Radiation Cooling Effects of Heat Conduction & Radiation Cooling #2 Conduction & Radiation Conduction Only MHD Temperature This is the case without the radiation but with the conduction. Density
DEM Differential Emission Measure (DEM) Derived from the Simulation Results Time • 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. Time
DEM: Comparison Time DEM Derived from the Simulation DEM Derived from the Observations Dere & Cook (1979) ( only initial part of the decay phase )
Light Curve & Energy Budget 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.
Parameter survey : Effect of plasma b Plasma Beta #0 • When the b is smaller, the cooling time is shorter.
Plasma Beta #1 If we assume is independent of at the start of the radiation cooling process • When the b is smaller, the cooling time is shorter. • Explanation radiation: energy balance in reconnection magnetic confinement & (Shibata & Yokoyama 1999)
Summary • 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.