Active region emergence and its effect on the solar corona

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