MAGNETIC TWIST OF EUV CORONAL LOOPS OBSERVED BY TRACE

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MAGNETIC TWIST OF EUV CORONAL LOOPS OBSERVED BY
TRACE

• RyunYoung Kwon, Jongchul Chae
• Astronomy Program, School of Earth and
  Environmental Science
• Seoul National University

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Whats the issue?
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Why does plasma of the coronal loop not disperse?
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Why does plasma of the coronal loop not disperse?
Magnetic Tension
Gas Pressure
Magnetic Tension
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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

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

• Pressure profile

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• Twist profile

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• Constant temperature (isothermal)
• Electron density profile
• Intensity profile
• FWHM
• Pressure excess

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Method

• 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

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Small Scale Field
Sample2

• Use TRACE MDI data taken by almost at the same
  time.
• Select 11 points
• align the TRACE and MDI

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FWHM
Pressure Excess
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Large Scale Field,
Linear Force Free (C.E. Alissandrakis, 1981)
SOHO/MDI 96minutes Magnetogram
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• 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.

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Field Strength
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Result
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Result
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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.

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Further Work

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

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REFERENCE

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