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Coronal Mass Ejections - the exhaust of modern dynamos

Coronal Mass Ejections - the exhaust of modern dynamos. Examples: systematic swirl (helicity) Measuring it quantitatively Connection with the dynamo Axel Brandenburg ( Nordita, Stockholm ). Examples of helical exhaust. Sigmoidal structures: North/South dependence. south.

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Coronal Mass Ejections - the exhaust of 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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