Coronal Magnetic Field – Force-Free Field and Topology

1. CSI 769 / ASTR 769 Lect. 04, Feb. 14 Spring 2008 Coronal Magnetic Field – Force-Free Field and Topology • 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

2. 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

3. Loop Arcade Loop arcade and formation of prominence (Van Ballegooijen & Martens, 1989)

4. Loop Arcade Loop arcade seen by TRACE (Credit: NASA)

5. Loop Arcade Force Free Field of a Sheared Arcade – Analytic Solution (Asch—Fig. 5.4)

6. Corona Loop: Width Almost constant width of coronal loops (Asch—Fig. 5.15)

7. Corona Loop: Width Coronal width models: loop width expansion ratio versus loop aspect ratio Sheared arcade Dipole loop Twisted flux tube (Asch—Fig 5.14)

8. Twisted Fluxtube Model (Asch—Fig. 5.16)

9. Twisted Fluxtube Model Geometry of Twisted Fluxtubs (Asch—Fig. 5.18)

10. Sigmoid Loops Sigmoids

11. Sigmoid Loops Forward S-shape Sigmoid Backward S-shape Sigmoid

12. Nullpoint & Separatrix (Asch—Fig. 5.22)

13. 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

14. The End