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