Nov. 8-11, th Solar-B science meeting Observational Analysis of the Relation between Coronal Loop Heating and Photospheric Magnetic Fields Y. Katsukawa and S. Tsuneta National Astronomical Observatory of Japan

Nov. 8-11, 20056th Solar-B science meeting2 Corona  B at photosphere Global relation between AR corona and magnetic fields has been well studied Fisher et al. (1998) Magnetic FluxSoft X-ray Corona Energy fluxMagnetic flux Yashiro et al. (2001)

Nov. 8-11, 20056th Solar-B science meeting3 Multi-temperature corona (in active regions) 2MK 1MK10MK5MK Coronal Temperature Transiently heated HotCool Steady loops What is the heating mechanism? flares, microflares (magnetic reconnection) Yoshida & Tsuneta (1996) (Nagata et al. 2003)

Nov. 8-11, 20056th Solar-B science meeting4 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

Nov. 8-11, 20056th Solar-B science meeting5 Vector magnetic field maps continuumfield strength inclinationazimuth

Nov. 8-11, 20056th Solar-B science meeting6 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 Identification of coronal loops (TRACE, SXT) Precise measurement of magnetic fields (ASP)

Nov. 8-11, 20056th Solar-B science meeting7 Observations with Spectro-Polarimeter Polarized light induced by the Zeeman effect Magnetic parameters of the photosphere –Intrinsic field strength –Inclination – Magnetic filling factor etc. I QVU

Nov. 8-11, 20056th Solar-B science meeting8 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

Nov. 8-11, 20056th Solar-B science meeting9 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. Soft X-ray EUV >2MK 1MK Hot loop conduction moss We can determine footpoint positions of hot loops using moss structure

Nov. 8-11, 20056th Solar-B science meeting10 Difference of magnetic parameters between Hot and Cool loops Moss (hot Loops) Cool Loops Field strength (kG) Inclination (deg)filling factorcontinuum intensity Similar Very different EFR Sunspot Non-spot

Nov. 8-11, 20056th Solar-B science meeting11 Formation of pores at the footpoints of the cool loops In f >0.4 regions, continuum intensities become dark. Signature of pores filling factor continuum intensity field strength (kG)

Nov. 8-11, 20056th Solar-B science meeting12 Temperature in the corona vs. Magnetic filling factor in the photosphere 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 Percentage of the area covered by the moss and the loop footpoints as a funciton of the magnetic filling factor

Nov. 8-11, 20056th Solar-B science meeting13 Hot loops magnetic elements 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 Cool loops Hot loopsCool loops Large energy inputSmall energy input

Nov. 8-11, 20056th Solar-B science meeting14 Heating rate as a function of the fill. factor 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 Coronal Heating Rate filling factor SunspotPlage Quiet Hot loopsCool loops

Nov. 8-11, 20056th Solar-B science meeting15 Fan-like cool loops above a sunspot (NOAA 10306) 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/continuumTRACE 171A/magnetogram Katsukawa et al. 2005, in preparation

Nov. 8-11, 20056th Solar-B science meeting16 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.

Nov. 8-11, 20056th Solar-B science meeting17 Identification of footpoint positions Loops and their footpoints are identified in TRACE 171A image. All loopsBright loops (I>4DN/pix/s) Mar Mar Mar Total4724

Nov. 8-11, 20056th Solar-B science meeting18 Umbra-Penumbra boundary region 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 I c is of the quiet Sun. umbra penumbra quiet Continuum intensity U-P boundary

Nov. 8-11, 20056th Solar-B science meeting19 Footpoint positions in terms of cont. intensity About a half of the loops have footpoints in the U-P boundary region. Umbral side is preferred rather than penumbra. Umbra11/4725% U-P boundary22/4747% Penumra13/4728% For all the loops Umbra8/2433% U-P boundary12/2450% Penumra4/2417% Only for the bright loops umbrapenumbra U-P boundary

Nov. 8-11, 20056th Solar-B science meeting20 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 UmbraPenumbra Umbra

Nov. 8-11, 20056th Solar-B science meeting21 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.

Nov. 8-11, 20056th Solar-B science meeting22 Footpoint positions and magnetic structure The footpoints of coronal loops are located where the spatial variability of continuum intensity is large. Positions of the footpoints Spatial variability of continuum intensity Interlaced magnetic structure in the photosphere is important in the heating of the coronal loops

Nov. 8-11, 20056th Solar-B science meeting23 Footpoint heating of the TRACE loops Two kinds of magnetic fields form interlaced configuration ⇒ discontinuity of magnetic fields ⇒ magnetic reconnection heat the base of the corona ⇒ TRACE loops umbrapenumbra Magnetic fields in the penumbra Magnetic fields in the umbra TRACE loops photosphere corona 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.

Nov. 8-11, 20056th Solar-B science meeting24 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 Aschwanden et al. (2000)

Nov. 8-11, 20056th Solar-B science meeting25 Signature of footpoint heating ? Vis. cont. UV cont.HαHe I ( K) 171A (FeIX/X)O IV ( K)Ne VI ( K)Mg IX ( K) Bright structures at the footpoints (Sunspot plume) Katsukawa et al. (2005) Images obtained with the CDS multi-wavelength observations of the spot

Nov. 8-11, 20056th Solar-B science meeting26 DEM at the loop footpoints (1) (2) (3) (1)(2)(3) Peak at K 1MK single temp. (1) (2) (3) O V (  K) Mg X (  K) Loops Foopoints

Nov. 8-11, 20056th Solar-B science meeting27 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.

Nov. 8-11, 20056th Solar-B science meeting28 International campaign observation in July, 2005 SOHO TRACE SST DOT VTT 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 Fe IX/X 171A EIT, CDS, MDI Shimizu et al. talk Kano et al. (P28)

Nov. 8-11, 20056th Solar-B science meeting29 TRACE loops emerging from decaying sunspots Two small decaying sunspots were observed for several days. The sunspots showed new kinds of the footpoint positions (1) Naked umbra (2) Light bridge

Nov. 8-11, 20056th Solar-B science meeting30 TRACE loops from the naked umbra Penumbrae had asymmetric distribution around the umbra. There was no penumbra on the northeastern side of the umbra. The strong magnetic fields in the umbra were directly interacting with surrounding granule.

Nov. 8-11, 20056th Solar-B science meeting31 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.

Nov. 8-11, 20056th Solar-B science meeting32 Magnetic structure in a light bridge 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. Leka (1997) See also the poster by Jurcak et al. (P15)

Nov. 8-11, 20056th Solar-B science meeting33 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 !!