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solar eclipse, 11.8.1999, Wendy Carlos and John Kern
Substructure of coronal loops?
Hardi Peter with
Craig de Forest
SwRI
Jim Klimchuk GSFC/NASA
Sven Bingert MPS
– field-line braiding – loop sub-structure – miniature loops
High-resolution Coronal Imager (Hi-C) – single rocket flight on 11 Jul 2012 (NASA/MSFC/CfA/LMSAL)
– imaging in 193 Å band identical to AIA/SDO – 6x higher resolution compared to AIA – 5 minutes of data from one active region – first results and description: Cirtain et al (2013) Nat. 493, 501
Hi-C AIA/SDO pixel size 0.1” 0.6” FOV ~400” full disk channel 193 Å 193 Å and many more
[ Fe XII ~1.5 MK ] time cadence 5.5 s 12 s obs. time: 5 min … years
AIA 193 Å image during Hi-C flight
Hi-C FOV
Cirt
ain
et a
l. (2
013)
Nat
. 493
, 501
Do we see field-line
braiding ?
Concept for coronal heating ► horizontal motions in photosphere as driver
→ field-line braiding (Parker 1972, ApJ 174, 499)
→ flux-tube tectonics (Priest et al 2002, ApJ 576, 533)
Hi-C rocket high-resolution EUV imaging 193 Å – Fe XII – 1.5 MK
► is there direct observational evidence for field-line braiding ?
? field-line braiding ?
Corona and chromosphere in Hi-C FOV → very complex active region: group with may spots
→ no “normal” nice large active region loops…
Is this field-line braiding for coronal loops ? Cirtain et al (2013) Nat 493, 501 argue that they saw field-line braiding…
– location: edge of penumbra
– close relation to chromospheric response
– no coronal loops around [ these issues were not discussed by Cirtain et al…]
– more probable: “mini-flare” type event (and there was a C-class flare from this region later…)
Hi-C 193 Å AIA 1600 Å
Cirt
ain
et a
l. (2
013)
Nat
. 493
, 501
Temporal evolution: chromosphere → corona AIA/SDO
Is this field-line braiding for coronal loops ? Cirtain et al (2013) Nat 493, 501 argue that they saw field-line braiding…
– location: edge of penumbra
– close relation to chromospheric response
– no coronal loops around [ these issues were not discussed by Cirtain et al…]
– more probable: “mini-flare” type event (and there was a C-class flare from this region later…)
Hi-C 193 Å AIA 1600 Å
Cirt
ain
et a
l. (2
013)
Nat
. 493
, 501
– this is an interesting event, but I am not convinced that this is field-line braiding
sub-structure of
coronal loops
Corona and chromosphere in Hi-C FOV → very complex active region: group with may spots
→ no “normal” nice large active region loops…
Comparison of Hi-C and AIA → clear difference plage region (upper left)
→ similar appearance in loop region
Comparison of Hi-C and AIA → clear difference plage region (upper left)
→ similar appearance in loop region Hi-C 193 Å
Comparison of Hi-C and AIA → clear difference plage region (upper left)
→ similar appearance in loop region AIA 193 Å
No sub-structure of loops ► Hi-C has more noise (higher resolution / less photons) ► no substructure visible in loops ! (within noise level)
0.2” x 0.2” → Hi-C resolution:
Der
e et
al.
(198
7) S
olar
Phy
s. 1
14, 2
23
corduroy trousers scenario
Multi-stranded loops ? classical multi-stranded loop scenario
r ~200 km
D
r ≲≲ D → few strands
hp 2
013
©
r < D → very many strands <
very fine
strands
Hi-C pixel size
~2 Mm
Morphological comparison to model observations show: (a) constant cross-section loops in expanding envelope (b) thin individual loops (c) thick non-expanding structures
3D MHD models show similar features
→ more work is needed for quantitative comparison…
miniature coronal loops
Smallest coronal structures ► Hi-C sees structures down to resolution limit ► are these “miniature coronal loops” ? 100x shorter than “normal” loops
→ length: 1.5”– 2” → width: 0.3”– 0.4”
0.2” x 0.2” → Hi-C resolution:
SDO context
Nature of the smallest coronal structures – footpoints of hot loops ?
probably not: where is the hot loop?! – really small loops ?
HMI shows “monopolar” region… but opposite polarities might be hidden…
15” x 15”
45” x 45”
Magnetic field on small scales: the photosphere
–1000
+1000
0
–400
+400
0
l.o.s
HMI / SDO (0.5”/pxl) IMaX/SUNRISE (0.05”/pxl) 40” x 40”
Wiegelmann et al (2010) ApJ 723, L185
comparison of HMI and IMaX, not showing the same structures…
≈0.6” SUNRISE data: opposite polarities with footpoint distance ≈ 1” within “unipolar” regions
4.5” x 4.5”
^
Observation of small “photospheric loops
4” x 2.3”
circular polarization
linear polarization
integrated light
time → Δt = 0 s 130 s 260 s Hinode/SOT Ishikawa et al (2010) ApJ 713, 1310
emerging flux in / around a granule 1- signal in lin. pol.
2- circ. pol. at sides
3- lin.pol. vanishes
^
corona photosphere interior
consistent with flux tube breaking through photosphere
^
Observation of small “photospheric loops
4” x 2.3”
circular polarization
linear polarization
integrated light
time → Δt = 0 s 130 s 260 s Hinode/SOT Ishikawa et al (2010) ApJ 713, 1310
emerging flux in / around a granule 1- signal in lin. pol.
2- circ. pol. at sides
3- lin.pol. vanishes
^
Ishi
kaw
a et
al (
2010
)
reconstruction of B at Δt = 130 s: is this a “photospheric loop” ?
Miniature coronal loops ?!
^
^
corona
chromosphere & photosphere
interior
~ 2 Mm
~ 2 Mm
≈ 2”
► there is observational evidence small magnetic loops that reach “into corona” ► such loops would be a bit bizarre: 6 Mm long, 2 Mm photosphere / chromosphere at both feet 2 Mm coronal part ► can such loops exist ?!
Conclusions
Conclusions
Substructure of coronal loops?
► claim to have observed field-line braiding might or might not be correct…
► coronal loops appear to have no substructure in Hi-C observations (0.2” spatial resolution)
→ either smooth structures → or very thin strands (much smaller that 100 km)
► tiny coronal loop-like structures exist (< 2 Mm)
→ are these miniature coronal loops?
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