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Solar and Heliospheric Physics. Magnetic Field Sep. 9 – Sep. 30, 2010. CSI 769 Fall 2010 Jie Zhang. Magnetic Fields. References: Aschwanden: Chap. 5.1 – 5.6. Supplement articles for PFSS model Altschuler, Martin D., Newkirk, Gordon, Jr., - PowerPoint PPT Presentation
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CSI 769 Fall 2010 Jie Zhang
Solar and Heliospheric Physics
Magnetic FieldSep. 9 – Sep. 30, 2010
References: •Aschwanden: Chap. 5.1 – 5.6
Supplement articles for PFSS model•Altschuler, Martin D., Newkirk, Gordon, Jr.,
•Magnetic Fields and the Structure of the Solar Corona, Solar Physics 9, 131-149, 1969
•Sakurai, Takashi.,•Green’s Function Methods for Potential Magnetic Fields, Solar Physics 76, 301-321, 1982
•Schrijver, Carolus J., Derosa, Marc K., •Photospheric and Heliospheric Magnetic Fields, Solar Physics, 212: 165-200, 2003
For NLFF model•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
Magnetic Fields
Corona in X-ray
•Why is the corona highly structured?
•Why is it hot?
•Why is it explosive?
Why?
Photospheric Magnetic Field•Magnetogram: measurement of magnetic in the photosphere•Nature of sunspot: areas of concentration of strong magnetic field
Magnetogram Continuum Image
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Hale’s Polarity Law
1. Sunspots are grouped in pairs of opposite polarities
2. The ordering of leading polarity/trailing polarity with respect to the east-west direction (direction of rotation) is the same in a given hemisphere, but is reversed from northern to southern hemisphere
3. The leading polarity of sunspots is the same as the polarity in the polar region of the same hemisphere
4. From one sunspot cycle to the next, the magnetic polarities of sunspot pairs undergo a reversal in each hemisphere. The Hale cycle is 22 years, while the sunspot cycle is 11 years
Hale’s Polarity Law
•Butterfly diagram of Magnetic Field•Global dipole field most of the time•Polar field reversal during the solar maximum
Solar Magnetic Cycle
Sporer’s Law: Sunspot emerge at relatively high latitudes and move towards the equator
Other Laws
Joy’s Law: The tilt angle of the active regions is proportional to the latitude
Solar Cycle•11-year cycle of sunspot number (SSN)•SSN is historically a good index of solar activity.•Correlate well with geomagnetic activities
•A diagram shows the position (latitude) of sunspot with time•It describe the movement of sunspot in the time scale of solar cycle
Butterfly Diagram of Sunspot
1. Sunspots do not appear at random over the surface of the sun.2. At any time, they are concentrated in two latitude bands on
either side of the equator. But these bands move with time3. At the start of a cycle, these bands form at mid-latitudes (~30°)4. As cycle progresses, they move toward the equator.5. As cycle progresses, sunspot bands becomes wider6. At the end of cycle, sunspots are close to equator and then
disappear7. At the minimum of the cycle, old cycle spots near the equator
overlaps in time with new cycle spots at high latitudes
Butterfly Diagram of Sunspot
Coronal Magnetic Field
Schrijver & Derosa, 2003
Coronal Magnetic Field
Feb. 2, 2008
http://www.lmsal.com/
forecast/index.html
Potential Field•Aschwanden 5.2•Unipolar field•Dipole field•Potential field calculation methods•Green’s function methods•Eigenfunction expansion methods•PFSS model
Single Sunspot Field•Aschwanden 5.2.1, P179-180
Result of the Analytical Model
Dipole Field•Aschwanden 5.2.2, P180 - 182
Result of the Analytical Model
Force-Free Field
•Force free field: Asch-Chap. 5.3.1•Non-Linear force free field: Asch-Chap. 5.3.3•Shear arcade: Asch-Chap. 5.3.2
•An example of linear force free field•Magnetic Nullpoints and Separators: Asch – Chap. 5.6
Loop Arcade
Loop arcade seen by TRACE (Credit: NASA)
Loop Arcade
Loop arcade seen by TRACE (Credit: NASA)
Loop Arcade
Loop arcade, shear motion, and formation of prominence (Van Ballegooijen & Martens, 1989)
Loop Arcade
Force Free Field of a Sheared Arcade – Analytic Solution (Asch—Fig. 5.4)
Nullpoint & Separatrix
(Asch—Fig. 5.22)
Nullpoints
2-D X-point (left) and O-point (Asch—Fig. 5.24)
Ref: Asch--Chap. 5.6.1
Priest—Chap. 1.3
The End