Evolution of Flare Ribbons and Energy Release Rate

1
IAU 223 Symposium, St. Petersburg, June 14 19
2004
Evolution of Flare Ribbons and Energy Release
Rate Ayumi ASAI1, Takaaki YOKOYAMA2, Masumi
SHIMOJO3, Satoshi MASUDA4, and Kazunari
SHIBATA1 1Kwasan and Hida Observatories, Kyoto
University 2Dept. of Earth and Planetary
Science, University of Tokyo 3Nobeyama Radio
Observatory, NAOJ 4Solar-Telestorial
Environment Laboratory, Nagoya University
Sartorius telescope _at_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.
Comparing Ha and HXR images, we found the
difference between the spatial distribution of
the Ha kernels and that of the HXR sources only
a few sources, which are accompanied by the Ha
kernels, are seen in the HXR images, while we can
see two-ribbon structure with many Ha kernels in
the Ha images.
HXR sources strong energy release
The difference between the spatial
distributions radiation sources are caused by the
difference of released energy.
Flare 2001 April 10, 0500UT _at_NOAA 9415 GOES
X2.3 Data HaKwasan Obs., Sartorius
Telescope MagnetogramSOHO / MDI hard-X ray
(HXR)Yohkoh / HXT MicrowaveNobeyama
Radioheliograph
Fig.2 Ha image overlaid with HXR contour image
other Ha kernels weak energy release
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 Ha
kernels, the difference of appearance can be
explained.
Fig1. Ha full disk image obtained with Flare
Monitoring Telescope at Hida Observatory
Here, we estimate the reconnection rate vfBp,
and the Poynting flux vfBp2 along the slits
which pass the HXR sources, as the
representations of the energy release rates.
2. ENERGY RELEASE RATE
Energy release rate (dE/dt) is written as
Bc coronal magnetic field strength vi
inflow velocity A area of reconnection region
Bcvi Bpvf
Reconnection rate
(Conservation of magnetic flux)
Bc2vi ? Bp2vf
Poynting Flux
(Bc?Bp is assumed)
newly reconnected loop
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).
We put slits in the direction of the flare ribbon
separation, and calculated vfBp and vfBp2 at
the outer edges of flare ribbons. We followed
the temporal evolutions of these values.
slit
Fig.3 Cartoon of magnetic reconnection
conservation of magnetic flux
Bc coronal magnetic field strength vf speed
of ribbon separation
flare ribbon
Fig.4 Method of the analyses
3. RESULTS
4. RED ASYMMETRY
1.5 A
-1.5 A
We examined spatially resolved red-asymmetry
distribution. Precipitation of nonthermal
particles cause downward motion of chromospheric
plasma ? reddening in Ha
slit I
slit II
slit II
slit I
red
blue
microwave
microwave
l
Fig.6 A spectrum at an Ha kernel
HXR
HXR
HXR burst at 0519UT
HXR burst at 0526UT
reconnection rate
intensity of kernel
reconnection rate
bright
Poynting flux
Poynting flux
The brighter kernel, the redder it is.
Red-asymmetry is stronger at HXR sources.
Fig.5 Time profiles of microwave (NoRH 17GHz),
HXR (Yohkoh/HXT), reconnection rate (vfBp), and
Poynting flux (vfBp2) for slit I (0519 UT
burst) and slit II (0526 UT burst).
(1) Temporal Evolution Qualitatively, both of
the estimated reconnection rates (vfBp) and
Poynting fluxes (vfBp2) reconstruct peaks of
the light curves of the nonthermal emissions.
dark
Fig.7 Scatter plot of reddening and Ha kernel
intensity
Iblue-Ired
red
blue
0
5. Summary
(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
Ha kernels.
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 radiation sources.
K2 HXR sources
K1
K2
K3
Table 1 Comparison of the reconnection rates and
the Poynting fluxes between the Ha kernels with
HXR sources and those without ones
We made extensive use of Yohkoh and SOHO MDI
Data Service.