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Dynamo-driven plasmoid ejections above a spherical surface

Dynamo-driven plasmoid ejections above a spherical surface . Jörn Warnecke 1,2 , Axel Brandenburg 1,2 and Dhrubaditya Mitra 1 1 Nordita, Stockholm, Sweden 2 Department of Astronomy, Stockholm University, Sweden. 1. Flux Emergence, CMEs and Flares. usually magnetic buoyancy

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Dynamo-driven plasmoid ejections above a spherical surface

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  1. Dynamo-driven plasmoid ejections above a spherical surface Jörn Warnecke1,2, Axel Brandenburg1,2 and Dhrubaditya Mitra1 1Nordita, Stockholm, Sweden 2 Department of Astronomy, Stockholm University, Sweden 1

  2. Flux Emergence, CMEsand Flares • usually magnetic buoyancy • but suppressed by downward pumping • (Nordlund et al 1992, Tobias et al 1998) • Turbulence can prevent flux tubes rising • (Käpylä et al. 2008) 2nd of december 2002 LASCO C2, SOHO • usually magnetic buoyancy • but suppressed by downward pumping • (Nordlund et al 1992, Tobias et al 1998) • Turbulence can prevent flux tubes rising • (Käpylä et al. 2008) SDO 7th of august 1972 Big Bear Solar Observatory 2

  3. Task • Spherical two layer system • (similar to Warnecke & Brandenburg, A&A 2010) • Magnetic field with turbulence in lower layer • Helical forcing to get large-scale field • and efficient dynamo action • Investigating flux emergence above the surface 3

  4. The Model The Pencil Code (Brandenburg & Dobler (2002) Comp Phys Comm 147, 471) • Induction equation • Continuum equation • Momentum equation • High-order modular code using MPI parallelisation („clusters“) • 128x128x64 Boundary conditions: • In ϕ periodic • Stress-free at all other boundaries • Density:r-> open,ϑ-> close • Bottom and ϑ: perfect conductor • Top: vertical-field 4

  5. - 29° Turbulent layer Outer Layer Θ - Forcing with helical transversal plane waves 0° + 0.7 Θ 1.0 Solar radii 29° 0° φ 17° 2.0 5

  6. Density stratification 6

  7. Results 7

  8. Dynamo Saturation and Oscillation Re=Rm=1.7 Saturation: τ > 500 at 1.2-1.7 of Beq Exponential growth: 100 < τ < 250 Dynamo Oscillation: ~ 200 τ 8

  9. <B>ϕfield lines as contours of rsin(θ) <Aϕ>ϕ and <Bϕ>ϕcolor-coded background Re=Rm=20 9

  10. Radial magnetic field at the surface Equator wards migration Re=Rm=20 10

  11. Current Helicity < JB >ϕ/<B2>ϕ Re=Rm=20 11

  12. The (Current) Helicity reverses its Sign in the Outer Atmosphere + - Re=Rm=20 Re=Rm=1.7 12

  13. Reversed Sign is supported by Observations Ulysses Brandenburg, Subramanian, Balogh & Goldstein, 2011 (submitted to ApJ) (arXiv:1101.1709) 13

  14. Conclusion • Dynamo: exponential growth, then saturationand oscillation. • Helicity reverses sign in the outer atmosphere, supported by Ulysses data. • Br at the surface: Equator wards migration. • Recurrent reconnection events • and magnetic cloud structures. • Massive plasmoid ejectionswith large helicity outburst. 14

  15. Future Work • Higher Reynolds numbers • Extend the domain in ϕand θ • Include convection in the turbulent layer • Open the top hydrodynamic boundaries • to get a solar wind solution • Extend the domain to in radial direction 15

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