Evolution of Flare Ribbons and Energy Release RateAyumi ASAI1,

Takaaki YOKOYAMA2, Masumi SHIMOJO3, Satoshi MASUDA4, and Kazunari SHIBATA1

1:Kwasan and Hida Observatories, Kyoto University 2:Dept. of Earth and Planetary Science, University of Tokyo

3:Nobeyama Radio Observatory, NAOJ 4:Solar-Telestorial Environment Laboratory, Nagoya University

1. INTRODUCTION

Magnetic reconnection is a key process for energy release and particle acceleration during solar flares. We quantitatively

estimated the amount of the released energy, based on the magnetic reconnection model and by using observable values.

We estimated the energy release rate, using ribbon-separation speeds and photospheric magnetic field. The temporal evolution of the estimated reconnection rate and the Poynting flux reproduced the nonthermal bursts. They are locally large enough at the HXR sources, which can explain the difference of spatial distributions of radiatio

n sources.

Fig.2 H image overlaid with HXR contour image

HXR sourcesstrong energy release

AvB

dt

dEi

c

4

2

2. ENERGY RELEASE RATE

Fig1. Hfull disk image obtained with Flare Monitoring Telescope at Hida Observatory

NOAA 9415

Energy release rate (dE/dt) is written as:

Bc : coronal magnetic field strength vi : inflow velocity A : area of reconnection region

3. RESULTS

The dynamic range of HXT is about10. Therefore, if the released energy at the HXR sources are (at least) 10 times larger than those at the other H kernels, the difference of appearance can be explained.

Fig.3 Cartoon of magnetic reconnection

We put slits in the direction of the flare ribbon separation, and calculated vf ・ Bp and vf ・ Bp

2 at the outer edges of flare ribbons. We followed the temporal evolut

ions of these values.

Fig.5 Time profiles of microwave (NoRH 17GHz), HXR (Yohkoh/HXT), reconnection rate (vf ・ Bp), and Poynting flux (vf ・ Bp2) for

slit I (05:19 UT burst) and slit II (05:26 UT burst).

(1) Temporal Evolution: Qualitatively, both of the estimated reconnection rates (vf ・ B

p) and Poynting fluxes (vf ・ Bp2) reconstruct peaks of the light curves of the nontherm

al emissions.

We made extensive use of Yohkoh and SOHO MDI Data Service.

Bc ・ vi = Bp ・ vf

Bc2 ・ vi ∝ Bp

2 ・ vf

Reconnection rate

Poynting Flux

(Conservation of magnetic flux)

(Bc B∝ p is assumed)

The difference between the spatial distributions radiation sources are

caused by the difference of released energy.

Comparing H and HXR images, we found the difference between the spatial distribution of the H kernels and that of the HXR

sources: only a few sources, which are accompanied by the H kernels, are seen in the HXR images, while we can see two-ribbon

structure with many H kernels in the H images.

IAU 223 Symposium, St. Petersburg, June 14 – 19 2004

Sartorius telescope @Kwasan Obs.

Flare2001 April 10, 05:00UT @NOAA 9415GOES X2.3DataH…Kwasan Obs., Sartorius TelescopeMagnetogram…SOHO / MDIhard-X ray (HXR)…Yohkoh / HXTMicrowave…Nobeyama Radioheliograph

Here, we estimate the reconnection rate vf ・ Bp, and the Poynting flux vf ・ Bp

2 along the slits which pass the HXR sources, as the representations of the energy release rates.

Bpvf

neutral line

other H kernelsweak energy release

Since it is difficult to estimate corona physical values (Bc, vi), by using the conservation law of magnetic flux, we estimate the energy release

rate with observable values (Bp, vf).

conservation of magnetic flux fpic vBvB flare ribbon

Bc : coronal magnetic field strengthvf : speed of ribbon separation

Fig.4 Method of the analyses

newly reconnected loop

microwave

HXR

reconnection rate

Poynting flux

HXR burst at 05:19UT

microwave

HXR

reconnection rate

Poynting flux

4. RED ASYMMETRY

slit I slit II

HXR burst at 05:26UT

slit I slit II

slit

(2) Spatial Distribution: Quantitatively, both of the reconnection rates and Poynting fluxes are enhanced enough (more than 10 times larger) at the HXR sources, compared with those at the other H kernels. Table 1 Comparison of the reconnection rates and the Poynting fluxes

between the H kernels with HXR sources and those without ones

reconnection rate (ratio)vf ・ Bp 　 [V m-1]

Poynting flux (ratio)vf ・ Bp

2 [erg cm-2 s-1]

K1 2.6×102 (0.52) 1.3×109 (0.27)

K2 7.7×103 (16) 7.6×1011 (150)

K3 4.9×102 (1.0) 5.0×109 (1.0)

K3

K1K2

K2 : HXR sources

5. Summary

+1.5 A-1.5 A

red blue

bright

dark

The brighter kernel, the redder it is. Red-asymmetry is stronger at HXR sources.

intensity of kernel

blue red

Iblue-Ired0

We examined spatially resolved red-asymmetry distribution. Precipitation of nonthermal particles cause downward motion of chromospheri

c plasma reddening in H

Fig.6 A spectrum at an H kernel

Fig.7 Scatter plot of reddening and Hkernel intensity