MAGNETIC TWIST OF EUV CORONAL LOOPS OBSERVED BY TRACE RyunYoung Kwon, Jongchul Chae Astronomy...
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Transcript of MAGNETIC TWIST OF EUV CORONAL LOOPS OBSERVED BY TRACE RyunYoung Kwon, Jongchul Chae Astronomy...
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”