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

Nov. 8-11, 200516th Solar-B science meeting

Observational Analysis of the Relation between Coronal Loop Heating and Photospheric Magnetic Fields

Y. Katsukawa and S. TsunetaNational Astronomical Observatory of Japan

Nov. 8-11, 2005 6th Solar-B science meeting 2

Corona B at photosphere

Global relation between AR corona and magnetic fields has been well studied

Fisher et al. (1998)

Magnetic Flux Soft X-ray Corona

BF Energy flux Magnetic flux

Yashiro et al. (2001)

Multi-temperature corona (in active regions)

2MK1MK 10MK5MK

Coronal Temperature

Transiently heatedHotCoolSteady loops

What is the heating mechanism?

flares, microflares(magnetic reconnection)

Yoshida & Tsuneta (1996)

(Nagata et al. 2003)

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

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)

Observations with Spectro-Polarimeter

Polarized light induced by the Zeeman effect

Magnetic parameters of the photosphere– Intrinsic field strength – Inclination– Magnetic filling factoretc.

I Q VU

magnmag

Hot and cool loops (NOAA 9231)

TRACE 171A1MK corona

Yohkoh/SXT>2MK corona

MDImag. flux in the photosphere

ASP FOV

Katsukawa and Tsuneta 2005, ApJ

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

1MK 1MK

Hot loop

conduction

We can determine footpoint positions of hot loops using moss structure

Difference of magnetic parameters between Hot and Cool loops

Moss (hot Loops)

Cool Loops

Field strength (kG) Inclination (deg) filling factor continuum intensity

Similar Very different

Sunspot

Non-spot

Formation of pores at the footpoints of the cool loops

In f >0.4 regions, continuum intensities become dark.

Signature of pores

filling factor filling factor

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

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 loops Cool loops

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 0.1-0.4

filling factor

SunspotPlageQuiet

10.10.01

tnt BBfvF4

Hot loops Cool loops

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/continuum TRACE 171A/magnetogram

Katsukawa et al. 2005, in preparation

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.

Identification of footpoint positions

Loops and their footpoints are identified in TRACE 171A image.

All loops Bright loops

(I>4DN/pix/s)

Mar. 11

Mar. 12

Mar. 13

Total 47 24

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 Ic is 0.2 - 0.7 of the quiet Sun.

penumbra

Continuum intensity

U-P boundary

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.

Umbra 11/47 25%

U-P boundary 22/47 47%

Penumra 13/47 28%

For all the loops

Umbra 8/24 33%

U-P boundary 12/24 50%

Penumra 4/24 17%

Only for the bright loops

umbra penumbra

U-P boundary

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

Umbra Penumbra PenumbraUmbra

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 .

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

tial v

Interlaced magnetic structure in the photosphere is important in the heating of the coronal loops

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

umbra penumbra

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.

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)

Signature of footpoint heating ?

Vis. cont. UV cont. Hα He I (104.5K)

171A (FeIX/X)O IV (105.2K) Ne VI (105.7K) Mg IX (106.0K)

Bright structures at the footpoints(Sunspot plume)

Katsukawa et al. (2005)

Images obtained with the CDS multi-wavelength observations of the spot

DEM at the loop footpoints

(1)(2)

(1) (2) (3)Peak at 105.5K 1MK single temp.

(1)(2)

O V (105.4K) Mg X (106.1K)

LoopsFoopoints

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.

International campaign observation in July, 2005

Ca II HG-bandG-contFe I 6302 mag.(H-alpha) G-band

Ca II HBlue/red cont.H alpha Spectro-polarimetry

He 10830A/FeI 1.5mFeI 6302A Fe IX/X 171A

EIT, CDS, MDI

Shimizu et al. talkKano et al. (P28)

TRACE loops emerging from decaying sunspots

Two small decaying sunspots were observed for several days.

TRACE TRACE WL 3-Jul-2005 06:12:41.000 UT

-140 -120 -100 -80 -60X (arcsecs)

TRACE TRACE 171 3-Jul-2005 06:13:20.000 UT

-140 -120 -100 -80 -60X (arcsecs)

20 40 60 80 100X (arcsecs)

U- Pboundary

nakedumbra

lightbridge

satellitepore

penumbra

The sunspots showed new kinds of the footpoint positions (1) Naked umbra (2) Light bridge

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.

-140 -120 -100 -80 -60X (arcsecs)

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.

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)

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 !!

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

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