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J. Büchner+collaborators, at different times, were:

Consequences of LHDI for three-dimensional collisionless reconnection through thin current sheets. J. Büchner+collaborators, at different times, were: J. Kuska, B. Nikutowski, I.Silin, Th.Wiegelmann all at: Max-Planck Institut für Sonnensystem-forschung in Katlenburg-Lindau, Germany

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J. Büchner+collaborators, at different times, were:

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  1. Consequences of LHDI for three-dimensional collisionless reconnection through thin current sheets J. Büchner+collaborators, at different times, were: J. Kuska, B. Nikutowski, I.Silin, Th.Wiegelmann all at: Max-Planck Institut für Sonnensystem-forschung in Katlenburg-Lindau, Germany (for „Solar System Research“ starting 1.7.2004 after being „for Aeronomy“ the last 40 years) Cambridge, August 20, 2004

  2. Topics Gradient and current-driven plasma instabilities in current sheets Initiation of 3D collisionless reconnection (PIC->Vlasov-simulation approach) in / through anti-parallel magnetic fields creation / annihilation of helicity density non-anti-parallel, finite guide magnetic field case asymmetric (magnetopause) current sheet case „Anomalous resistivity“ approach to introduce kinetic results into large scale MHD EUV Bright Points (BP): MHD modeling of the dynamic evolution (photospheric flows) + anomalous transport => Null point <or> finite B <or> QSL reconnection ??? Cambridge, August 20, 2004

  3. 3D current sheet instabilities 1970th: quasi/linear theory: LHD-instability at the edges (Drake, Huba, Davidson, Winske, Tanaka & Sato ... ) 1996: 3D PIC simulations showed: global (kink/sausage) mode current sheet instabilities can initiate reconnection (Pritchett et al.; Zhu & Winglee; Büchner & Kuska 1996) 1998...now: New theory - and simulation results about current-driven and drift instabilities at sheet center (Horiuchi & Sato; Büchner, Kuska & Silin; Daughton et al.) Our latest move: From PIC to Vlasov-codes to test wave-particle interactions, resonances etc. which can initiate current sheet instabilities and reconnection Cambridge, August 20, 2004

  4. Kinetic stability investigation Vlasov equation: Linear perturbation of distribution functions Resulting perturbation of density and current Maxwell equations for the fields or wave equation for the potentials Cambridge, August 20, 2004

  5. Linear stability of oblique eigenmodes at current sheet center -> > 20o: Eigenmodes are linearily stable(k=k0 cos ex +k0 sin ey) Cambridge, August 20, 2004

  6. Vlasov simulation code Cambridge, August 20, 2004

  7. Nonlinear LHDI (anti-parallel fields: Vlasov kinetic simulation) Cambridge, August 20, 2004

  8. Non-local penetration of LHD unstable waves Cambridge, August 20, 2004

  9. Simulation shows: the Ey fluctuations grow also at the center Cambridge, August 20, 2004

  10. Drift-resonance instability (DRI) 1D ion distribution in the current direction 1D electron distribution in the current direction Ions drive waves → plateau-formation →electron-heating Cambridge, August 20, 2004

  11. DRI: 3D distribution function 3D Ion distribution function 3D electron distribution Cambridge, August 20, 2004

  12. 3D current sheet instability (Plasma density perturbation; case of antiparallel fields) Cambridge, August 20, 2004

  13. Current sheet thickness C1<->C4 (7.9.01, 19:00>23:00) Cambridge, August 20, 2004

  14. Current sheet waves ~21:00 UT Cambridge, August 20, 2004

  15. Current sheet waves –observed by Cluster as predicted Cambridge, August 20, 2004

  16. Waves initiate 3D reconnection Cambridge, August 20, 2004

  17. Mechanism:Wave- reconnection coupling: Dashed: LHDI (edge) ; Solid: LHDI at the center; Dashed-dotted: reconnecting mode Cambridge, August 20, 2004

  18. 3D reconnection island: Cambridge, August 20, 2004

  19. 2.) Helicity density evolution: a.) 3D antiparallel reconnection Spheres: quadrants 1 and 4 Squares: quadrants 2 and 3 Solid line - total helicity: Cambridge, August 20, 2004

  20. Antiparallel -> finite guide field By guide field By -> flux ropes Quadrupolar By field -> Bending of B-fields Cambridge, August 20, 2004

  21. Finite guide field case -> non 180o magnetic shear Positive Co-helicity HMo > 0 Guide fields change the shear angle between the ambient B-fields 180o Negative Co-helicity HMo < 0 (J = direction of sheet current and of reconnection E- field) Cambridge, August 20, 2004

  22. 3D guide field reconnection: initially positive co-helicity case t = 1 t = 25 Cambridge, August 20, 2004

  23. 2D / 3D positive co-helicity reconnection („pull reconnection“) Dotted: quadrants 1 and 4 Dashed: quadrants 2 and 3 Solid line - total helicity: Cambridge, August 20, 2004

  24. 3D guide field reconnection: initially negative co-helicity case t = 1 t = 23 Cambridge, August 20, 2004

  25. 2D / 3D negative co-helicity reconnection („push reconnection“) Dotted: quadrants 1 and 4 Dashed: quadrants 2 and 3 Solid line - total helicity: Cambridge, August 20, 2004

  26. 3.) Resonant DRI in the guide field case: For stronger guide fields the cross-field propagation direction turns further away from the current direction. The growth rate of the instability decreases proportionally to the number of resonant ions. Cambridge, August 20, 2004

  27. Reconnection wave in a non- anti-parallel (guide field) current sheet Bz in log presentation turbulence -> structure Bz in linear presentation for the polarity of magnetic bubbles Cambridge, August 20, 2004

  28. Result: patchy reconnection in the non-anti-parallel, guide field case: The B field opens the boundary throug local patches (blue: below, red: above) Cambridge, August 20, 2004

  29. 4: Non-symmetric case (MP) Simulation model The pressure being locally balanced; drift Maxwellians, drifts currents -> fields rotate through a tangential magnetic boundary Cambridge, August 20, 2004

  30. Instability of a non-symmetric magnetic boundary current sheet Magnetic field Bz: LHD instability first on magnetospheric side (z<0) -> penetrates to the magnetosheath side (z>0) and triggers reconnection - island formation Cambridge, August 20, 2004

  31. Magnetopause observation (Cluster) A. Vaivads et al., 2004 Cambridge, August 20, 2004

  32. 5.) Quasilinear estimate of the WP momentum exchange (-> “anomalous collision frequency;-> “... resistivity”) (Davidson and Gladd, Phys. Fluids, 1975) Cambridge, August 20, 2004

  33. Anomalous momentum exchangedue to nonlinear DRI in a current sheet: Cambridge, August 20, 2004

  34. 6.) X-ray & EUV Bright Points (BPs): quiet-sun reconnection XBP are formed inside diffuse clouds, which grow at 1 km/s up to 20 Mm and then form a bright core 3 Mm wide, they last, typically, 8 h Vaiana, 1970: rockets; Golub et al. 1974-77: Skylab More recently: SOHO and TRACE observations -Later (Soho...) : also many EUV BP investigated > BP are assumed to be prime candidates for reconnection: they well correlate with separated photospheric dipolar (opposite polarity) photospheric magnetic fluxes Cambridge, August 20, 2004

  35. Soho-MDI and EIT: EUV BP 17-18.10.1996 (M. Madjarska et al., 2003) MDI line-of sight magnetic field ( 40” x 40”) EIT (195 A) same field of view Cambridge, August 20, 2004

  36. Reconnection models for BP Due to the B separation in the photosphere -> Reconnection between bipoles assumed to take place in the corona, -> magnetohydrostatic models, e.g. Newly Emerging Flux Model (EMF) Heyvaerts, Priest & Rust 1977 Converging flux model Priest, Parnell, Martin & Gollup, 1994 Separator Reconnection in MCC Longcope, 1998 Cambridge, August 20, 2004

  37. But: dynamical footpoint motion: -> currents are driven into the chromosphere/corona Cambridge, August 20, 2004

  38. Model, starting with extrapolated B-fields ... Cambridge, August 20, 2004

  39. ... and footpoint motion (here after 1:39 ...and density-heightUT 18.10.96): profile (VAL): Cambridge, August 20, 2004

  40. Density Evolution -> t=128 Cambridge, August 20, 2004

  41. Parallel electric fields and parallel currents at t=128 Cambridge, August 20, 2004

  42. Transition region parallel electric fields Cambridge, August 20, 2004

  43. Transition region reconnection Cambridge, August 20, 2004

  44. Reconnection due to resistivity switched on enhanced current (velocity) Cambridge, August 20, 2004

  45. Not at a null, but between two nulls (separator through 35,20,5 ?) <- Iso- surfaces of a small total magnetic field, hence embedding the nulls Cambridge, August 20, 2004

  46. Further work planned on: • Current sheet instabilities for more realistic current and field models and their consequences for reconnection • resulting anomalous transport as an approach toward quantifying the coupling between MHD and kinetic scales for solar and magnetospheric applications • Reconnection at neutral points vs. separator reconnection vs. quasi-separatrix layer - reconnection in the course of the dynamically evolving „magnetic carpet“ („tectonics“) Cambridge, August 20, 2004

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