1. solar eclipse, 11.8.1999, Wendy Carlos and John Kern Structure of solar coronal loops: from miniature to large-scale Hardi Peter Max Planck Institute for Solar System Research Germany peter@mps.mpg.de S. Bingert, J. A. Klimchuk, C. de Forest, J. W. Cirtain, L. Golub, A. R. Winebarger, K. Kobayashi, K. E. Korreck – miniature loops – sub-structure of loops A&A in press / arXiv 1306.4685

2. AIA 193 Å image during Hi-C flight Hi-C FOV Cirtain et al. (2013) Nat. 493, 501

3. Corona and chromosphere in Hi-C FOV → very complex active region: group with may spots → no “normal” nice large active region loops…

4. miniature coronal loops miniature coronal loops

5. Small 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:

6. SDO context Nature of the small 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”

7. Magnetic field on small scales: the photosphere –1000 vertical magnetic field [G] +1000 0 –400 +400 0 l.o.s magnetic field [G] HMI / SDO (0.5”/pxl)IMaX/S UNRISE (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” S UNRISE data: opposite polarities with footpoint distance ≈ 1” within “unipolar” regions 4.5” x 4.5” 15” x 15” miniature loop

8. Miniature coronal loops ?! ^ ^ corona chromosphere & photosphere interior ~ 2 Mm ≈ 2” ► there is observational evidence small magnetic loops that reach “into corona” e.g. Ishikawa et al (2010) ApJ 713, 1310 ► can such loops exist ?!

9. sub-structure of coronal loops sub-structure of coronal loops

10. Corona and chromosphere in Hi-C FOV → very complex active region: group with may spots → no “normal” nice large active region loops…

11. Comparison of Hi-C and AIA → clear difference in plage region (upper left) → similar appearance in loop region Hi-C 193 Å

12. Comparison of Hi-C and AIA → clear difference in plage region (upper left) → similar appearance in loop region AIA 193 Å

13. 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:

14. Getting a lower limit for the strand diameter diameter of individual strands number of strands in whole loop: Either strands have to be smaller than 15 km or the loop is monolithic !

15. Visualization of strands and cross-loop profile Hi-C AIA integrate along Y – apply PSF – bin to AIA/Hi-C pixel size

16. 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… See also talk by Feng Chen on Wed morning: “A coupled model for the formation of active region corona”

17. Conclusions

18. Structure of solar coronal loops: from miniature to large-scale ► tiny coronal loop-like structures exist (loop length below 2 Mm) → are these miniature coronal loops? → how are they connected to the photosphere ? → how are they sustained ? ► long 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)

20. 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 size0.1” 0.6” FOV~400” full disk channel193 Å 193 Å and many more [ Fe XII ~1.5 MK ] time cadence5.5 s 12 s obs. time:5 min … years

21. 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”

22. ^ Observation of small “photospheric loops 4” x 2.3” circular polarization linear polarization integrated light time →  t = 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

23. ^ Observation of small “photospheric loops 4” x 2.3” circular polarization linear polarization integrated light time →  t = 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 ^ Ishikawa et al (2010) reconstruction of B at  t = 130 s: is this a “photospheric loop” ?

24. Size of structures across the loop

25. Dere et al. (1987) Solar Phys. 114, 223 corduroy trousers scenario Multi-stranded loops ? classical multi-stranded loop scenario r ~200 km D r ≲ D → few strands hp 2013 © r < D → very many strands < very fine strands Hi-C pixel size ~2 Mm