1. MAGNETIC TWIST OF EUV CORONAL LOOPS OBSERVED BY TRACE RyunYoung Kwon, Jongchul Chae Astronomy Program, School of Earth and Environmental Science Seoul National University

2. 2005 July2 What’s the issue? Sample1 Sample3 Sample2 2000.07.25 08:00 2000.09.30 18:37 2004.04.04 05:01

3. 2005 July3 Why does plasma of the coronal loop not disperse? Gas Pressure Magnetic Pressure By gas pressure? By magnetic pressure? So far these have been no reported observational evidence.

4. 2005 July4 Why does plasma of the coronal loop not disperse? Gas Pressure Magnetic Tension

5. 2005 July5 Method We decompose the coronal magnetic field B into a large- scale component B 0 and small-scale component B 1 Using the force-free condition for the large-scale field The magnetohydrostatic equation describing the force balance across a loop at the small scale is given by Pressure profile

6. 2005 July6 Twist profile Axial Field Strength Pressure Excess Loop Width

7. 2005 July7 Constant temperature (isothermal) Electron density profile Intensity profile FWHM Pressure excess

8. 2005 July8 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

9. 2005 July9 Sample2 Small Scale Field Use TRACE & MDI data taken by almost at the same time. Select 11 points align the TRACE and MDI

10. 2005 July10

11. 2005 July11 1 2 3 FWHM 1 2 3 Pressure Excess

12. 2005 July12 Large Scale Field, Linear Force Free (C.E. Alissandrakis, 1981) SOHO/MDI 96minutes Magnetogram

13. 2005 July13 Large Scale Field,

14. 2005 July14 Large Scale Field, 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.

15. 2005 July15

16. 2005 July16 Field Strength 1 2 3

17. 2005 July17 Result 1 2 3

18. 2005 July18 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

19. 2005 July19 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.

20. 2005 July20 Further Work We will extend this work to a number of EUV loops observed by TRACE and X-ray loops observed by Yohkoh.

21. 2005 July21 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”