1. 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

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. 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

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

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

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