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?