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Supersonic downflows in the photosphere
discovered in sunspot moat regions
T. Shimizu (ISAS/JAXA, Japan),
V. Martinez-Pillet, M. Collados,
B. Ruiz-Cobo, R. Centeno (IAC, Spain),
C. Beck (KIS, Germany),
Y. Katsukawa (NAOJ, Japan)
Report a discovery from international time program
observation at Canaries islands on July 2005
2005/11/08
6th Solar-B Science Meeting@Kyoto
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Remarkable Stokes V profiles we have found!
Photospheric Si I 10827A by TIP
400mA => 11km/s!!


Slit direction
wavelength
Extremely red-shifted signal
Frequently observed in sunspot moat regions.
2005/11/08
6th Solar-B Science Meeting@Kyoto
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Observations

Tenerife Infrared Polarimter
(TIP; Martinez Pillet et al. 1999)
– Attached to German VTT, Tenerife
– Four Stokes profiles of photospheric Si I
line at 10827A (g=1.5)

Polarimetric Littrow Spectrograph
(POLIS; Beck et al. 2005)
– Simultaneous mapping of four Stokes of
Fe I 6301.5A(g=1.67)/6302.5A (g=2.5)
– Note: same spectral lines measured with
Solar-B Spectro-Polarimter

TIP Stokes I
Si I 10827
He I 10830
POLIS Stokes I
Fe I 6301.5 Fe I 6302.5
VTT
Leading spot of AR 10781 on 3 July
2005
2005/11/08
6th Solar-B Science Meeting@Kyoto
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Morphological properties of downflows (1)

Location of extremely red-shifted events
40“x45“ FOV
([enhanced] magnetogram generated from Stokes V data)


“25 events” were found in three scan maps of a sunspot
moat region.
I
Red-shifted signal has oppositepolarity near the edge of sunspot
Q
(positive)-polarity flux patches
U
– 11 of 25 near the edge of positive-flux patch
– 19 of 25 opposite-polarity red-shifted signal
2005/11/08
6th Solar-B Science Meeting@Kyoto
V
3.4”
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Morphological properties of downflows (2)

Size extremely small-scale phenomena
– Scan direction: 0.9 – 1.2 arcsec (3 – 4 scan positions, 0.3” step)
– Slit direction: 0.7 – 1.0 arcsec (4-6 pixels, 0.17”/pix)

Duration <1hr, but exactly unknown because of slit scanning
observation

Observed not only in Si line but also in Fe 630nm lines
– Si I 10827A + Fe I 6301.5 + FeI 6302.5
– Si I 10827A + Fe I 6301.5 only
– Si I 10827A only
TIP: Si 10827A
I
500mA
16 event (64%)
2 event ( 8%)
7 event (28%)
POLIS: Fe I 6301.5/6302.5A
300mA
Q
U
2005/11/08
V
3.4”
6th Solar-B Science Meeting@Kyoto
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Estimate physical conditions

SIR inversion was applied to 7 events (Dr. Ruiz-Cobo)
– 3 lines are simultaneously fitted
– Assumed to have two magnetic components with constant parameters
(magnetic field, velocity), and 2 different temperatures, one for each
magnetic component.
Event 1-0 pos 6

Preliminary comfortable
results have been derived
for only limited number of
events.
2005/11/08
6th Solar-B Science Meeting@Kyoto
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Estimate physical conditions

The downflowing component has a higher field strength
than the rest component, and it has relative downflows as
large as 10 km/s. Also, the downflowing component seems
to be hot by some 100 K or so.
Event 1-0 pos 6
Rest
magnetic
component
Downflowing
magnetic
component
1072
1533
2.6
12.2
Inclination (deg)
156
180
Temperature (K)
solid
dotted
B (gauss)
v (km/s)
2005/11/08
6th Solar-B Science Meeting@Kyoto
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Discussions

downflows as large as 10 km/s
– Compared with sound speed ~5 km/s (T~5500K)
Alfven speed ~16 km/s (B~1500g, n~ 7x10^-8 g/cm3)
– The observed downflows are supersonic but slightly below Alfven
speed.

We currently think that the observed supersonic downflows may be a
signature of downwarding outflow from magnetic reconnections
occurring at the chromosphere or upper photosphere.

No “transient” brightenings were
observed in TRACE 171A
coronal images.
Dutch Open Telescope
Ca II H movie for map 1
(9:05-9:35UT, same FOV)
2005/11/08
6th Solar-B Science Meeting@Kyoto
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Summary

We found events with extremely red-shifted Stokes V signal
in sunspot moat regions. They have following properties:
– Measured with photospheric Si I 10827A line but also with Fe I
630nm lines.
– In order of one arcsec or smaller size.
– As large as 10 km/s, which is supersonic but still below Alfven
speed.
– The downflowing component has a higher field strength than the
rest component, and seems to be hot by some 100 K or so.

The observed supersonic downflows may be a signature of
downwarding outflow from magnetic reconnections
occurring at the chromosphere or upper photosphere.
2005/11/08
6th Solar-B Science Meeting@Kyoto
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Further investigations with Solar-B



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Full Stokes of Fe I 630nm lines will be measured in higher
spatial resolution (0.16arcsec) with SOT/FPP SpectroPolarimter.
Further understanding of this new phenomenon can be
provided with Solar-B coordinated observations among
SOT spectro-polarimter, filter imagers, and EIS.
Complicated Stokes profiles will be expected much more
frequently. Some may be caused by flux tube dynamics,
predicted by simulation (Steiner et al.).
Inversions of Stokes profiles will play key roles in
interpreting such Stokes profiles.
2005/11/08
6th Solar-B Science Meeting@Kyoto
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