1. Evolution of Flare Ribbons and Energy Release
Magnetic Reconnection Hyogo, March 8 – 10, 2005
Evolution of Flare Ribbons and Energy Release
Ayumi Asai1, T. Yokoyama T.2, M. Shimojo1, S. Masuda3, and K. Shibata4
1: Nobeyama Radio Observatory, NAOJ
2: Dept. of Earth and Planetary Science, University of Tokyo
3: Solar-Terrestrial Environment Laboratory, Nagoya University
4: Kwasan and Hida Observatories, Kyoto University
Sartorius telescope
@Kwasan Obs.
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.
Energy release rate (dE/dt) is written as:
Bc : coronal magnetic field strength
vi : inflow velocity
A : area of reconnection region
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).
Flare
2001 April 10, 9415
GOES X2.3
Data
Ha…Kwasan Obs., Sartorius Telescope
Magnetogram…SOHO / MDI
hard-X ray (HXR)…Yohkoh / HXT
Microwave…
Nobeyama Radioheliograph
NOAA 9415
Fig.2 Cartoon of magnetic reconnection
conservation of
magnetic flux
Bc : coronal magnetic field strength
vf : speed of ribbon separation
Reconnection rate
Bc・vi = Bp・vf
(Conservation of magnetic flux)
Fig1. Ha full disk image obtained with Flare Monitoring Telescope at Hida Obs.
Poynting Flux
Bc2・vi ∝ Bp2・vf
(Bc∝Bp is assumed)
2. ENERGY RELEASE RATE
slit I
slit II
slit II
We put slits in the direction of the flare ribbon separation, and calculated vf・Bp and vf・Bp2 at the outer edges of flare ribbons. We followed the temporal evolutions of these values.
slit I
microwave
microwave
HXR
HXR
HXR burst at 05:19UT
HXR burst at 05:26UT
neutral line
newly reconnected loop
reconnection rate
reconnection rate Bp vf
Poynting flux
Poynting flux
slit
Fig.4 Time profiles of microwave (NoRH), 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) Qualitatively, both of the estimated reconnection rates (vf・Bp) and Poynting fluxes (vf・Bp2) reconstruct peaks of the light curves of the nonthermal emissions.
flare ribbon
Fig.3 Method of the analyses
The spatial distribution of the Ha kernels is different from that of the HXR sources. The dynamic range of HXT is about10.
reconnection rate (ratio)
vf・Bp　[V m-1]
Poynting flux (ratio)
vf・Bp2 [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)
Table 1 Comparison of the reconnection rates and the Poynting fluxes between the Ha kernels with HXR sources and those without ones
So, the released energy at the HXR sources of (at least) 10 times larger than those at the other Ha kernels can explain the difference of appearance.
HXR sources
strong energy release K1 K2 K3
(2) 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 Ha kernels.
Fig.5 Ha image overlaid with HXR contour image
other Ha kernels
weak energy release
3. RED ASYMMETRY
4. SUMMARY
We examined spatially resolved red-asymmetry distribution. Precipitation of nonthermal particles cause downward motion of chromospheric plasma  reddening in Ha
flux tube
We estimated the energy release rate, by 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 radiation sources.
We examined spatially resolved red-asymmetry distribution.
Ha kernel
Reddening is conspicuous at the edge of flare ribbons
blue
red l
-1.5 A
+1.5 A
Fig.7 Spatial distribution of red-asymmetry
Fig.6 A spectrum at an Ha kernel
The brighter kernel, the redder it is.
bright
bright
Normalized red-asymmetry no correlation with intensity.
Downward vel. ~ constant
intensity of kernel
intensity of kernel
red
blue
Fig.8 Scatter plot of reddening and Ha kernel intensity
dark
red
dark
blue
Iblue-Ired
(Iblue-Ired)/(Iblue+Ired)/2
We made extensive use of Yohkoh and SOHO MDI Data Service.