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Coronal Magnetic Field – Force-Free Field and Topology
CSI 769 / ASTR 769 Lect. 04, Feb. 14 Spring 2008
References: •Aschwanden: Chap. 5.3 – 5.6
Articles: • Schrijver et al. 2006, Solar Physics 235, P161-190
“Non-Linear Force Free Modeling of Coronal magnetic Fields Part 1: A Quantitative Comparison of Methods
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Force-Free Field
•Force free field: Asch-Chap. 5.31•Non-Linear force free field: Asch-Chap. 5.3.3•Shear arcade: Asch-Chap. 5.3.2•An example of linear force free field
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Loop Arcade
Loop arcade and formation of prominence (Van Ballegooijen & Martens, 1989)
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Loop Arcade
Loop arcade seen by TRACE (Credit: NASA)
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Loop Arcade
Force Free Field of a Sheared Arcade – Analytic Solution (Asch—Fig. 5.4)
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Corona Loop: Width
Almost constant width of coronal loops (Asch—Fig. 5.15)
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Coronal width models: loop width expansion ratio versus loop aspect ratio
Sheared arcade
Dipole loop
Twisted flux tube
(Asch—Fig 5.14)
Corona Loop: Width
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Twisted Fluxtube Model
(Asch—Fig. 5.16)
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Geometry of Twisted Fluxtubs (Asch—Fig. 5.18)
Twisted Fluxtube Model
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Sigmoid Loops
Sigmoids
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Sigmoid Loops
Forward S-shape Sigmoid Backward S-shape Sigmoid
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Nullpoint & Separatrix
(Asch—Fig. 5.22)
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X-point Model
2-D X-point (left) and O-point (Asch—Fig. 5.24)
Ref: Asch--Chap. 5.6.1
Priest—Chap. 1.3
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The End