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Active region emergence and its effect on the solar corona

Active region emergence and its effect on the solar corona. Dana Longcope Montana State University, Bozeman, MT. Thanks. Isaac Klapper B. Ravindra* Brian Welsch §. George Fisher (UCB) Alex Pevtsov (NSO). MSU. § Presently UCB. * Presently IIA. Active regions: where they come from.

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Active region emergence and its effect on the solar corona

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  1. Active region emergence and its effect on the solar corona Dana Longcope Montana State University, Bozeman, MT Thanks • Isaac Klapper • B. Ravindra* • Brian Welsch§ • George Fisher (UCB) • Alex Pevtsov (NSO) MSU § Presently UCB * Presently IIA

  2. Active regions: where they come from Typical AR: 8968 movie Babcock 1961 MDI

  3. F F F grow separate

  4. various sizes... F ... same story F

  5. How do these emerging flux tubes affect the corona? Outline • Dynamics of emergence • Twist (helicity) in emerging tubes • Transport of helicity into the corona by emerging tubes

  6. Dynamics of rising flux tubes • Isolated tube, pressure-confined, “thin”  a << Hp • Axis of tube: space curve x(s,t) • Dynamical equations: Spruit 1981, Choudhuri & Gilman 1987

  7. Model evolution of AR tubes • Initialize tube at base of CZ • Follow evolution of emerging • tube - thin FT eqns. • Predict configuration of • observed AR D’Silva & Choudhuri 1993 Fan et al. 1994

  8. Deflection of rising tube by Coriolis effect  tilted pair of spots A Rising Flux Tube

  9. D’Silva & Choudhuri 1993 Thin flux tube successes: • Hale’s polarity law • Joy’s law for tilt angles • (D’Silva & Choudhuri 1993) • p-f asymmetry • (Fan et al. 1993) • post-emergence velocities • (Moreno-Insertis et al 1994) • Statistical dispersion • (Longcope & Fisher 1996) Moreno-Insertis et al. 1994

  10. Flux Tube Twist Flux tubes must be twisted in order to rise (Parker 1979) Moreno-Insertis & Emonet 1996 twisted untwisted Abbett et al. 2000

  11. ... and AR fields are twisted (from Nakagawa et al. 1971) (courtesy T. Magara & Hinode)

  12. Evidence that flux tubes emerge already twisted: Flux (F) and current increase together (Leka et al. 1996 ) curr. F curr. F

  13. How twisted are the tubes? • abestintroduced by • Pevtsov, Canfield • & Metcalf (1995) • calcB^(a)by extrapolating • Bz w/ fixed value ofa • varya until B^(a)best • matches observed B^ • i.e. minimize

  14. How twisted are the tubes? <abest>~ 3 x 10-9 m-1 varies /w latitude Dabest~ 10-8 m-1 independent of latitude Linear trend removed (from Longcope, Fisher & Pevtsov 1998)

  15. Piddington 1978 Twist in flux tubes J q s Bz v Field lines twist about axis at a rate q(s,t) “=“ dq/ds Plasma spinsabout axis at rate w(s,t) “=“ dq/dt Axis of tube: B= qr Bz a= 2q v= r

  16. Twist in flux tubes J q s Bz v Evolution of twist & spin Axis of tube: k (Longcope & Klapper 1997)

  17. Dynamics of twist Out-of-plane motion of axis S(s) indep. of q or w

  18. Axis-twist coupling • Increasing LH • writhe (dWr/dt <0 ) • Increasing RH twist (dTw/dt > 0)

  19. Writhe from Turbulence: The S-effect (Longcope, Fisher & Pevtsov 1998) Spectrum of kinetic helicity Twist source Averaging over turbulence: Variance of twist source:

  20. S-effect vs. -effect Spectrum of kinetic helicity Compare to a-effect:

  21. Cause of the observed twist Observed properties Twist in CZ flux tube LH twist in North <a> ~ 3 x 10-9 m-1 25% violation of trend Da~ 10-8 m-1 Da indep. of latitude • Writhe from CZ turbu-lence: The S-effect • Kinetic helicity: • RH writhe in North • <a> ~ 3 x 10-9 m-1 • Fluctuates (turbulence) • Level indep. of latitude • Da~ 10-8 m-1

  22. Twist: Photosphere vs. Corona Force-free-field w/ constant- Pevtsov, Canfield & McClymont (1997) abest ~ain coronal field • best andfor 140 ARs • Found best correlated with 

  23. Coupling flux tube to corona Low-b coronal Equilibrium: FFF High-b CZ Field: twisted Thin flux tube

  24. Coupling flux tube to corona Balance of net torque Current matches across interface a  a=2q in corona in tube (Longcope & Weslch 1998)

  25. Coupling flux tube to corona Imbalanced torque (shunted current) spin shunt spinning

  26. Flux tube twist  sunspot rotation movie Evershed 1910 1 deg/hr Brown et al. 2003

  27. Twist Creates Spin TRACE White Light channel TRACE 171A (1MK) movie (Courtesy D. Alexander)

  28. Spin from Emergence simple model: Longcope & Welsch 1998 • Twist propagates • into corona

  29. Spin from Emergence simple model: Longcope & Welsch 1998 • Twist propagates • into corona • Twist-rarefaction • waves propagates • inward to CZ

  30. Spin from Emergence simple model: Longcope & Welsch 1998 • Twist propagates • into corona • Twist-rarefaction • waves propagates • inward to CZ • Characteristic • time-scale for • adjustment: d/vA ~ 1 day

  31. Spin from Emergence Observation: Pevtsov, Maleev & Longcope 2003 Fit Model to Data v=264 m/s a = 2 10-8 m-1 vA = 158 m/s

  32. Spin from Emergence Observation: Pevtsov, Maleev & Longcope 2003 AR8582 AR8817

  33. Measured Velocity • Bz measured: LOS mg • U measured: LCT of Bz • A0 extrapolated = +3 X 1040 Mx2/day = F2 10-2/day (Chae 2001)

  34. Longcope, Ravindra & Barnes 2007 Measuring Spin • partition m-gram • v(x) from LCT • cf WL rotation from Brown et al. 2003

  35. Measuring Spin spin braiding 1 12 2 2

  36. Measuring Spin P01 Brown et al. 2003 all contributions to dH/dt

  37. fit: q = -0.67 x 10-8 m-1 Hbr separation d(t) H Hsp • Helicity dominated by braiding • Northern AR: • H > 0 Hsp < 0 Longcope & Welsch model

  38. fit: q = +2.3 x 10-8 m-1 Longcope & Welsch model separation d(t) Hsp H Hbr • Helicity dominated by spin • Southern AR: • H > 0 Hsp > 0

  39. Helicity Injection

  40. Long term helicity injection (from van Driel-Gesztelyi, Demoulin & Mandrini, 2003)

  41. Helicity Flux in ARs • Differential rotation: • Th. (DeVore 2000): ~ 3 X 10-3/day • Obs. (Demoulin et al 2002) ~3 X 10-4 • Proper motions: (observations) • LCT (van Driel-Gesztelyi et al. 2003) ~10-2 • Sunspot rotation (Brown et al 2003)  ~10-1

  42. Summary • ARs created by emergence of flux tubes • Tubes consist of twisted flux -- twisted by turbulence during rising (-effect) • Helicity of twist propagates into corona • Observed proper motions (rotating sunspots) consistent with twist propagation

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