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CSI 769 Fall 2010 Jie Zhang

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.,

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CSI 769 Fall 2010 Jie Zhang

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  1. Solar and Heliospheric Physics Magnetic Field Sep. 9 – Sep. 30, 2010 CSI 769 Fall 2010 Jie Zhang

  2. Magnetic Fields • 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

  3. Why? • Why is the corona highly structured? • Why is it hot? • Why is it explosive? Corona in X-ray

  4. Photospheric Magnetic Field • Magnetogram: measurement of magnetic in the photosphere • Nature of sunspot: areas of concentration of strong magnetic field Magnetogram Continuum Image

  5. Hale’s Polarity Law + - + - + + - + - -

  6. Hale’s Polarity Law • Sunspots are grouped in pairs of opposite polarities • 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 • The leading polarity of sunspots is the same as the polarity in the polar region of the same hemisphere • 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

  7. Solar Magnetic Cycle • Butterfly diagram of Magnetic Field • Global dipole field most of the time • Polar field reversal during the solar maximum

  8. Other Laws Sporer’s Law: Sunspot emerge at relatively high latitudes and move towards the equator Joy’s Law: The tilt angle of the active regions is proportional to the latitude

  9. Solar Cycle • 11-year cycle of sunspot number (SSN) • SSN is historically a good index of solar activity. • Correlate well with geomagnetic activities

  10. Butterfly Diagram of Sunspot • A diagram shows the position (latitude) of sunspot with time • It describe the movement of sunspot in the time scale of solar cycle

  11. Butterfly Diagram of Sunspot • Sunspots do not appear at random over the surface of the sun. • At any time, they are concentrated in two latitude bands on either side of the equator. But these bands move with time • At the start of a cycle, these bands form at mid-latitudes (~30°) • As cycle progresses, they move toward the equator. • As cycle progresses, sunspot bands becomes wider • At the end of cycle, sunspots are close to equator and then disappear • At the minimum of the cycle, old cycle spots near the equator overlaps in time with new cycle spots at high latitudes

  12. Coronal Magnetic Field Schrijver & Derosa, 2003

  13. Coronal Magnetic Field Feb. 2, 2008 http://www.lmsal.com/forecast/index.html

  14. Potential Field • Aschwanden 5.2 • Unipolar field • Dipole field • Potential field calculation methods • Green’s function methods • Eigenfunction expansion methods • PFSS model

  15. Single Sunspot Field • Aschwanden 5.2.1, P179-180 Result of the Analytical Model

  16. Dipole Field • Aschwanden 5.2.2, P180 - 182 Result of the Analytical Model

  17. 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

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

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

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

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

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

  23. Nullpoints 2-D X-point (left) and O-point (Asch—Fig. 5.24) Ref: Asch--Chap. 5.6.1 Priest—Chap. 1.3

  24. The End

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