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

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

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. 5.6.1

Priest—Chap. 1.3

The End