MAGNETIC TWIST OF EUV CORONAL LOOPS

OBSERVED BY TRACE

RyunYoung Kwon, Jongchul Chae

Astronomy Program, School of Earth and Environmental Science

Seoul National University

2005 July 2

What’s the issue?Sample1

Sample3

Sample2

2000.07.25 08:00

2000.09.30 18:37

2004.04.04 05:01

2005 July 3

Why does plasma of the coronal loop not disperse?

Gas Pressure

Gas Pressure

Gas PressureGas Pressure

Magnetic Pressure

Magnetic PressureBy gas pressure? By magnetic pressure?

So far these have been no reported observational evidence.

2005 July 4

Why does plasma of the coronal loop not disperse?

Gas Pressure

Magnetic Tension

Magnetic Tension

2005 July 5

Method• We decompose the coronal magnetic field B into a

large-scale component B0 and small-scale component B1

• Using the force-free condition for the large-scale field

00 BB

zzB ˆ)(00B ˆ),(ˆ),( 11 zrBzzrB z 1B

• The magnetohydrostatic equation describing the force balance across a loop at the small scale is given by

04

)8

( 11

r

BBp

r

• Pressure profile

22 ))/(1()(

ar

pprp e

2005 July 6

• Twist profile

L

r

r

dzaB

p

aB

p

dz

d

araB

p

dz

d

00

0

00

20

8

8

)/(1

18

• Axial Field Strength

• Pressure Excess

• Loop Width

0B

pa

zr

p

p

a

0B

2005 July 7

• Constant temperature (isothermal)• Electron density profile

• Intensity profile

• FWHM

• Pressure excess

Tk

pn

Tk

pn

ar

nnn

BB

ee 2

& 2

,))/(1( 1022

10

5.32 ))/)((1()(

axx

IIxI

c

pext

a94.0

TkTc

Ip B

p

)(

|sin|2

data. nalobservatio from B and p a,

parameters three thedetermine will weNow

0

2005 July 8

• Large Scale Field– Linear Force Free Model

• Small Scale Field– Twisted Flux Tube Model

• Combining the large-scale and small-scale yields the twist of the loop.

• Data– TRACE EUV(17.1nm) Data– SOHO/MDI 96minutes Magnetogram

Method

2005 July 9

Sample2

Small Scale Field

• Use TRACE & MDI data taken by almost at the same time.

• Select 11 points

• align the TRACE and MDI

2005 July 10

5.32 ))/)((1()(

axx

IIxI

c

pext

2005 July 11

1

2

3

FWHM

1

2

3

pPressure Excess

2005 July 12

Large Scale Field,

00 BB

Linear Force Free(C.E. Alissandrakis, 1981)

0B

SOHO/MDI 96minutes Magnetogram

2005 July 13

0z Mmz 3.4

Mmz 7.8 Mmz 0.13

Large Scale Field, 0B

2005 July 14

2

1

2 ))(())((1

oi

N

iioii YsYXsX

Nd

Large Scale Field, 0B

• To find the field line that best matches the loop,

• we calculate a number of field lines using linear force-free extrapolations with different values of force-free alpha.

• we choose the field line that minimizes by the distance d between the loop and the curve.

2005 July 15

-33 Mm1050.8

2005 July 16

Field Strength

1

2

3

2005 July 17

Result

1 2

3

2005 July 18

Result

0.02020.01620.0089 (Mm)

2.522.241.6 (rad)

0.070.170.21Mean ( )

1.432.531.93Mean FWHM (Mm)

81.6146.4157.77Mean field strength (G)

124.9138.6298.91Total length L (Mm)

sample3sample2sample1　

2 cmdynp

L

2005 July 19

Conclusion

• The on-axis magnetic twist of the loop is found to be about from 1.5 to 2.5 which corresponds to a winding number about from 0.75 to 1.25.

• There is a tendency that the twist in the middle of the loop is larger than both footpoint.

2005 July 20

Further Work

• We will extend this work to a number of EUV loops observed by TRACE and X-ray loops observed by Yohkoh.

2005 July 21

REFERENCE

• Jongchul Chae, 2005, ApJ, in press• C. E. Alissandrakis, 1981, A&A, 100, 197• Handy, B. N., et al 1999, Sol. Phys., 187, 229• Priest, E. R. 1982, “Solar Magnetohydrodynamics”