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Y. Katsukawa and S. Tsuneta National Astronomical Observatory of Japan

Observational Analysis of the Relation between Coronal Loop Heating and Photospheric Magnetic Fields. Y. Katsukawa and S. Tsuneta National Astronomical Observatory of Japan. Magnetic Flux. Soft X-ray Corona. Corona  B at photosphere.

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Y. Katsukawa and S. Tsuneta National Astronomical Observatory of Japan

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  1. Observational Analysis of the Relation between Coronal Loop Heating and Photospheric Magnetic Fields Y. Katsukawa and S. Tsuneta National Astronomical Observatory of Japan 6th Solar-B science meeting

  2. Magnetic Flux Soft X-ray Corona Corona  B at photosphere • Global relation between AR corona and magnetic fields has been well studied Fisher et al. (1998) Yashiro et al. (2001) Energy flux Magnetic flux 6th Solar-B science meeting

  3. Multi-temperature corona (in active regions) Coronal Temperature 1MK 5MK 10MK 2MK Transiently heated Cool Hot Steady loops flares, microflares (magnetic reconnection) (Nagata et al. 2003) What is the heating mechanism? Yoshida & Tsuneta (1996) 6th Solar-B science meeting

  4. Falconer et al. (1997, 2000) Relation between Magnetic shear and bright SXT loops • Schmieder et al. (2004) In EFR, spatial and temporal distribution of SXT and TRACE loops were studied 6th Solar-B science meeting

  5. Identification of coronal loops (TRACE, SXT) Precise measurement of magnetic fields (ASP) Magnetic fields at the footpoints of coronal loops • Magnetic energy is generated in the photosphere by the interaction between convection and magnetic fields. The energy is transported to the corona along magnetic field lines. • To understand coronal heating, it is important to resolve structure in the corona (i.e. coronal loops), and study magnetic properties at the footpoints of the coronal loops. • Today’s talik (1) Difference of magnetic properties between hot and cool loops (2) Magnetic structure at the footpoints of the cool loops 6th Solar-B science meeting

  6. Observations with Spectro-Polarimeter • Polarized light induced by the Zeeman effect • Magnetic parameters of the photosphere • Intrinsic field strength • Inclination • Magnetic filling factor etc. Q U V I 6th Solar-B science meeting

  7. Hot and cool loops (NOAA 9231) TRACE 171A 1MK corona Yohkoh/SXT >2MK corona MDI mag. flux in the photosphere ASP FOV Katsukawa and Tsuneta 2005, ApJ 6th Solar-B science meeting

  8. >2MK Soft X-ray Hot loop EUV conduction moss 1MK 1MK Moss = Footpoints of hot loops • Patchy low-lying EUV structure at the footpoints of hot loops • The base of the corona is heated by heat conduction from the overlying hot corona. We can determine footpoint positions of hot loops using moss structure 6th Solar-B science meeting

  9. Very different Difference of magnetic parameters between Hot and Cool loops Moss (hot Loops) EFR Non-spot Cool Loops Sunspot Non-spot Field strength (kG) Inclination (deg) filling factor continuum intensity Similar 6th Solar-B science meeting

  10. field strength (kG) continuum intensity filling factor filling factor Formation of pores at the footpoints of the cool loops • In f >0.4 regions, continuum intensities become dark. • Signature of pores 6th Solar-B science meeting

  11. Temperature in the corona vs. Magnetic filling factor in the photosphere Percentage of the area covered by the moss and the loop footpoints as a funciton of the magnetic filling factor • There are HOT corona above about 30 % of f <0.4 regions in the photosphere. • The cool loops can be seen only above ｆ>0.3 regions in the photosphere. • In high f regions, there are little COOL plasma (<10%) as well as HOT plasma 6th Solar-B science meeting

  12. magnetic elements Hot loops Cool loops Large energy input Small energy input Hot loops Cool loops Magnetic elements and filling factor • Photospheric magnetic properties of the hot and cool loops • Magnetic filling factors are very different • Photospheric magnetic fields consist of fine magnetic elements. Their diameter is around 100km filling factor  number density 6th Solar-B science meeting

  13. Heating rate as a function of the fill. factor Plage Sunspot Quiet • In the quiet sun, the heating should be small. The much lower filling factor (0.01) might make the energy input small. • There is a peak of the heating rate around the filling factor 0.1-0.4 Hot loops Cool loops Coronal Heating Rate 0.01 0.1 1 filling factor 6th Solar-B science meeting

  14. Fan-like cool loops above a sunspot (NOAA 10306) Katsukawa et al. 2005, in preparation • Steady coronal loops radially extending from the sunspot • The temperature of the loops is 1MK • Life time is a few hours • Many loops have their feet near the boundary of the umbra. TRACE 171A/continuum TRACE 171A/magnetogram 6th Solar-B science meeting

  15. How to determine the positions of the footpoints • 2nd derivatives of intensity profiles are calculated along each loop. • The position where 2nd derivative = 0 is regarded as the footpoint position. 6th Solar-B science meeting

  16. Identification of footpoint positions • Loops and their footpoints are identified in TRACE 171A image. 6th Solar-B science meeting

  17. U-P boundary Umbra-Penumbra boundary region quiet • Histogram of continuum intensity shows 3 peaks corresponding to umbra, penumbra, and the quiet sun. • The Umbra-Penumbra (U-P) boundary region is defined as where Ic is 0.2 - 0.7 of the quiet Sun. penumbra umbra Continuum intensity 6th Solar-B science meeting

  18. Footpoint positions in terms of cont. intensity For all the loops • About a half of the loops have footpoints in the U-P boundary region. • Umbral side is preferred rather than penumbra. umbra penumbra U-P boundary Only for the bright loops 6th Solar-B science meeting

  19. Umbra Penumbra Umbra Penumbra Correlation between continuum intensity and magnetic fields • In the U-P boundary region, the field strength and the inclination have negative and positive correlation with the continuum intensity. Umbra  Strong and vertical fields Penumbra  Weak and inclined fields 6th Solar-B science meeting

  20. Magnetic structure in the U-P boundary • Along the U-P boundary, there is spatial fluctuation of the continuum intensity. Field strength and inclination also fluctuate simultaneously. Interlaced magnetic structure with the spatial scale of 3000 – 4000km . 6th Solar-B science meeting

  21. Positions of the footpoints Footpoint positions and magnetic structure • The footpoints of coronal loops are located where the spatial variability of continuum intensity is large. Spatial variability of continuum intensity Interlaced magnetic structure in the photosphere is important in the heating of the coronal loops 6th Solar-B science meeting

  22. Footpoint heating of the TRACE loops TRACE loops Magnetic fields in the umbra Two kinds of magnetic fields form interlaced configuration ⇒ discontinuity of magnetic fields ⇒ magnetic reconnection heat the base of the corona ⇒TRACE loops Magnetic fields in the penumbra corona photosphere umbra penumbra Interlaced magnetic structure is more pronounced in penumbrae, but the mag field lines might not reach the corona since the magnetic fields are nearly horizontal there. 6th Solar-B science meeting

  23. Aschwanden et al. (2000) Temperature distribution along TRACE loops • TRACE gives nearly flat temperature profiles along loops.  Heating is concentrated at their footpoints • The heating mechanism suggested here is consistent with such observations 6th Solar-B science meeting

  24. Signature of footpoint heating ? Images obtained with the CDS multi-wavelength observations of the spot UV cont. Hα He I (104.5K) Vis. cont. O IV (105.2K) Ne VI (105.7K) Mg IX (106.0K) 171A (FeIX/X) Bright structures at the footpoints (Sunspot plume) Katsukawa et al. (2005) 6th Solar-B science meeting

  25. DEM at the loop footpoints O V (105.4K) Mg X (106.1K) (1) (1) (2) (2) (3) (3) (1) (2) (3) 1MK single temp. Peak at 105.5K Loops Foopoints 6th Solar-B science meeting

  26. Summary of the TRACE cool loops • Coronal loops seen in the TRACE 171A images have footpoints mostly in the U-P boundary region. • Interlaced magnetic structure in the photosphere is important in the heating of the coronal loops. • Strong EUV emissions from the transition region were observed at the footpoints in the sunspot. 6th Solar-B science meeting

  27. International campaign observation in July, 2005 SST DOT VTT SOHO EIT, CDS, MDI Ca II H G-band G-cont Fe I 6302 mag. (H-alpha) G-band Ca II H Blue/red cont. H alpha Spectro-polarimetry He 10830A/FeI 1.5m FeI 6302A Shimizu et al. talk Kano et al. (P28) TRACE Fe IX/X 171A 6th Solar-B science meeting

  28. The sunspots showed new kinds of the footpoint positions (1) Naked umbra (2) Light bridge TRACE loops emerging from decaying sunspots • Two small decaying sunspots were observed for several days. 6th Solar-B science meeting

  29. TRACE loops from the naked umbra • Penumbrae had asymmetric distribution around the umbra. • There was no penumbra on the northeastern side of the umbra. Thestrong magnetic fields in the umbra were directly interacting with surrounding granule. 6th Solar-B science meeting

  30. Light bridge and TRACE loops • The TRACE loops were clearly associated with the formation of the light bridge. • After the formation of the light bridge, it became relatively darker above the light bridge in the TRACE images. 6th Solar-B science meeting

  31. Magnetic structure in a light bridge Leka (1997) • In the light bridges, there are relatively weak and inclined magnetic fields close to the vertical umbral fields. • The situation is similar to the U-P boundary region. See also the poster by Jurcak et al. (P15) 6th Solar-B science meeting

  32. Summary and target of Solar-B • We have found some key magnetic features in the heating of the coronal loops. • But, those observations suggest that sub-arcsec structure in the photosphere is important in the heating. (Spatial resolution is not enough to resolve such fine structure with ASP used in our work) Clarify the relationship between fine magnetic structures and the heating with Solar-B !! 6th Solar-B science meeting

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