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Dynamo-Driven Plasmoid Ejections Above a Spherical Surface: Insights from Turbulent Dynamo Models

This study explores the dynamo-driven plasmoid ejections occurring above a spherical surface, using advanced turbulent dynamo models. We investigate flux emergence, magnetic buoyancy, and the suppression of upward magnetic flow due to downward pumping. Our model employs the Pencil Code, analyzing magnetic field behavior and turbulence interactions in a two-layer spherical system. Key findings reveal dynamo saturation, oscillation dynamics, and current helicity reversal linked to observational data from the Ulysses spacecraft. Future work will extend model parameters and domains for improved solar wind predictions.

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Dynamo-Driven Plasmoid Ejections Above a Spherical Surface: Insights from Turbulent Dynamo Models

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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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