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, P “Non-Linear Force Free Modeling of Coronal magnetic Fields Part 1: A Quantitative Comparison of Methods

Force-Free Field Force free field: Asch-Chap Non-Linear force free field: Asch-Chap Shear arcade: Asch-Chap An example of linear force free field

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

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

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

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

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

Twisted Fluxtube Model (Asch—Fig. 5.16)

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

Sigmoid Loops Sigmoids

Sigmoid Loops Forward S-shape Sigmoid Backward S-shape Sigmoid

Nullpoint & Separatrix (Asch—Fig. 5.22)

X-point Model 2-D X-point (left) and O-point (Asch—Fig. 5.24) Ref: Asch--Chap Priest—Chap. 1.3

The End