Direct Observations of the Magnetic Reconnection

Direct Observations of the Magnetic
Reconnection Site of an Eruption on
2003 November 18
2005,ApJ, 622,1251
J. Lin, Y.-K. Ko, L. Sui, J. C. Raymond, G. A.
Stenborg, Y. Jiang, S. Zhao, and S. Mancuso
2005/11/28 太陽雑誌会 <short> 長島薫
Solar Seminar (Zasshikai)
NAGASHIMA Kaori
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<1.Introduction>
Since the timescale of
magnetic dissipation or
reconnection is longer than
that of the catastrophe (i.e.,
the Alfven timescale ), the
development of a long
current sheet is expected
during major eruptions.
reconnection
In this study, a direct
inflow
current sheet &
observation of the current
reconnection
sheet and the associated
outflow
reconnection process is
reported.
part of Fig.1 Schematic diagram of a disrupted
magnetic field forming in an eruptive process.
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<2.Observations & Results>
Observations
an eruptive event
– occurred on 2003 Nov. 18
– on the east limb (between NOAA AR 0507
& 0508)
DATA:
•SOHO/EIT 195Å & RHESSI
– observation of the initial stage & subsequent
development of the eruption in the lower corona
•SOHO/UVCS, LASCO & MLSO MK4
– observation of the consequences in the higher
corona
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EIT 195Å
movies
current sheet (fig2)
flare loop (fig2) non-movie
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composite of LASCO C2 (17:50) ,
MK4(17:49) ,& EIT 195Å (17:48) images
This figure
resembles the typical
Kopp-Pneuman
configuration for
major flares (Kopp &
Pneuman 1976), in
which the postflare/CME loops are
located under the
cusp structure at the
lower tip of the
current sheet.
Fig. 8
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after the wavelet-based intensity
contrast enhancement (WICE)
before the WICE
WICE → good at emphasizing the fine
features of large-scale structure.
（Stenborg & Cobelli 2003 A&A）
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LASCO C2
movie
•enhanced by the wavelet
(WICE) technique
Fine structures
•leading edge & core of CME
•current sheet
•the helical structure around
the CME core
fig4 (~12hr)
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<2. Observations & Results>
Inflow Velocity & Reconnection rate
• Following Yokoyama et al.(2001), the
inflow velocity can be measured using the
motion of two legs of the arcade system
observed by EIT.
• However, the structure seen in the EIT
images is diffuse and the apparent inward
motion was suggested that actually due to
the changing position of the X-type
reconnection region rather than inflow.
(Chen et al. 2004)
• Therefore, in this study, they use the UVCS
observations to determine
the inflow speed.
Yokoyama et al. 2001 part of Fig.4
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Fig.5
EIT 195Å (10:14)
UVCS Lyα(slit scan)
LASCO C2 (10:26)
using WICE
The width of a
dark gap seen in
the left UVCS
image decreased
with time.
time
magnetic
reconnection
inflow
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*dark gap ⇔ current sheet
<2. Observations & Results>
Inflow Velocity & Reconnection rate
•The dark gap (not a no emission region but a lower Lyα
intensity region) could result from a higher
temperature or a significant outflow speed.
•The Lyα width in the gap is considerably larger than in
the outside of it. This suggests higher temperature in
the gap. However, this temperature (6.7e6 K) require a
density above 1e8 /cm^3 to account for the Lyα
intensity. This is inconsistent with no FeXVIII signal.
•Smaller density also can be a cause of darkening, but
the modest density enhancement was observed in the
LASCO images.
•Then, the low emission is due to Doppler dimming.
•An outflow speed of 200 km/s would account for the low
intensity in the gap. (large line width⇔LOS comp. of
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outflow.)
<2. Observations & Results>
Inflow Velocity & Reconnection rate
Lyα intensity
north
time
the center
of gap ~ P.A.
=95°
south
Position Angle [deg.]
Inflow velocity
can be
deduced by
comparing the
widths of the
gap every two
successive
times.
inflow
velocity VR :
10.5-106 km/s
Fig.11a 5 Lyαintensity profiles along the UVCS
slit taken at 1.70Rsun 10:04-10:14 UT.
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north :
blueshift
(~20km/s)
an evidence
for the
reconnection
inflow
south :
redshift
(~35km/s)
LOS ⊥inflow
No Doppler shift
inflow
inflow
the center
of the gap
Wavelength [A]
Fig. 12 averaged over 10:04-10:14
When the field
lines adjoining the
CS are tilted ...
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<2. Observations & Results>
Inflow Velocity & Reconnection rate
• Outflow velocity : 460-1075 km/s
– Several bright blobs successively flowed away from
the Sun along a long thin streamer-like feature
observed by LASCO C2 & C3.
– the thin feature ⇔ current sheet (CS)
– the blobs ⇔ outflow of reconnection inside the CS
• Assuming an incompressible plasma, the
outflow velocity is equal to VA (the local Alfven
speed in the reconnection region).
• Therefore, the reconnection rate MA=VR/VA is
in the range from 0.01 to 0.23. (However the real
value of MA should vary over a wider range.)
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Summary
• an erupitive process
– direct observation of CS, inflow, and outflow
– an energetic CME
– the CME & the flare are connected by a
stretched current sheet.
– the average reconnection inflow :10.5106km/s (using the UVCS Lyα data )
– Lyα profiles around the gap are shifted.
• a direct evidence of the reconnection inflow?
– the average outflow : 460-1075km/s (blob)
– the reconnection rate :0.01-0.23
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