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Unveiling Coronal Mass Ejections: Insights into Modern Dynamos

Explore the systematic swirls of magnetic helicity related to coronal mass ejections. Learn about key research by Axel Brandenburg and others, including helical exhaust structures and magnetic field dynamics. Discover the significance of helicity conservation and the complexities of modern dynamos.

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Unveiling Coronal Mass Ejections: Insights into Modern Dynamos

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  1. Coronal Mass Ejections - the exhaust of modern dynamos Examples: systematic swirl (helicity) Measuring it quantitatively Connection with the dynamo Axel Brandenburg (Nordita, Stockholm)

  2. Examples ofhelical exhaust

  3. Sigmoidal structures:North/Southdependence south

  4. Sigmoidal filaments (from S. Gibson)

  5. Magnetic helicity

  6. Flux crossings + J. Chae (2000, ApJ) + + + - -

  7. It’s a popular logo too…

  8. Magnetic helicity from crossings J. Chae (2000, ApJ) + + - -

  9. Current helicity and magn. hel. Flux Bao & Zhang (1998), neg. in north, plus in south (also Seehafer 1990) Berger & Ruzmaikin (2000) S DeVore (2000) N (for BR & CME)

  10. Helicity in Magnetic Clouds From fits to a linear force-free field Lynch et al. (2005)

  11. Helicity from time series Matthaeus et al. (1982)

  12. Nindos et al. (2003)

  13. Nindos & Andrews (2004)

  14. Magnetic helicity conservation How J diverges as h0 Ideal limit and ideal case similar!

  15. No helicity production by flowsbut segragation in space: Generates toroidal from poloidal field H<0 Poloidal field regenerated by tilting (Coriolis force) H>0

  16. Twisting an existing tube:segragation in spectral space

  17. Cancelling magn helicityintroduced in single tube + -

  18. a-effect dynamos (large scale) New loop Cyclonic convection; Buoyant flux tubes Differential rotation (prehelioseism: faster inside) Equatorward migration  a-effect ?need meridional circulation

  19. Tilt  pol. field regeneration standard dynamo picture  internal twist as dynamo feedback N-shaped (north) S-shaped (south)

  20. Production of LS helicity forcing produces and But no net helicity production therefore:  alpha effect Yousef & Brandenburg A&A 407, 7 (2003)

  21. Problems with a-effect • Catastrophic quenching?? • a ~ Rm-1, ht ~ Rm-1 • Field strength vanishingly small!?! • Something wrong with simulations • so let’s ignore the problem • Possible reasons: • Suppression of lagrangian chaos? • Suffocation from small scale magnetic helicity?

  22. Connection with a effect: writhe with internal twist as by-product a effect produces helical field W clockwise tilt (right handed)  left handed internal twist both for thermal/magnetic buoyancy

  23. Simulations: forced turbulence w/shear Negative current helicity: net production in northern hemisphere 1046 Mx2/cycle Brandenburg & Sandin (2004, A&A 427, 13) Helicity fluxes from shear: Vishniac & Cho (2001, ApJ 550, 752) Subramanian & Brandenburg (2004, PRL 93, 20500)

  24. Saturation: 50% energy in large scales azimuthally averaged no helicity, e.g. Rogachevskii & Kleeorin (2003, 2004) geometry here relevant to the sun neg helicity (northern hem.)

  25. Conclusion • 11 yr cycle • Dyamo (SS vs LS) • Problems • a-quenching • slow saturation • Solution • Modern a-effect theory • j.b contribution • Magnetic helicity fluxes • Location of dynamo • Distrubtion, shaped by • near-surface shear 1046 Mx2/cycle

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