Flux Collision Models of Prominence Formation

1. Flux Collision Models of Prominence Formation Brian Welsch (UCB-SSL), Rick DeVore & Spiro Antiochos (NRL-DC) Filament imaged by NRL’s VAULT II (courtesy A.Vourlidas)

2. Essentials of prominence field: • Sheared field parallel to PIL. • Dipped or helical field lines, to support mass. (But cf. Karpen, et al., 2001!) • Overlying field restraining sheared field. Q: Does the topological structure of prominences form above photosphere?

3. Previously, DeVore & Antiochos (2000) sheared a potential dipole, and got a prominence-like field. • Requires shear along PIL. • Velocity efficiently injects helicity. • No eruption: not quadrupolar. • Q: Where does shear originate?

4. Following MacKay et al. (1999), Galsgaard and Longbottom (2000) collided two flux systems… …and got reconnection & some helical field lines

5. Initial Topology in Galsgaard & Longbottom’s Model

6. The Martens & Zwaan Model • Initially, bipoles do not share flux. • Diff’l Rot’n in, e.g., N.Hemisphere drives reconnection between bipoles’ flux systems. • Reconnection converts weakly sheared flux to strongly sheared flux

7. But there are two ways the field can reconnect! Left: “strapping” field restrains prominence field. Right: underlying field subducted? (Martens & Zwaan) Q: What determines how the field reconnects?

8. A: Helicity! Reconnection preserves H, so initial & reconnected fields have same helicity. H < 0 H > 0 For config. at left, start w/negative helicity , etc. Q: Which config matches the Sun?

9. Shearing adds positive helicity! • With potential initial fields, shearing-induced reconnection leads to H > 0 state. • To get H < 0 state, try twisting fields prior to shearing, to model interaction of fields that emerged with H < 0. Two types of runs: A) Sheared; B) Twisted, then sheared.

10. Plan A: Given two initially unconnected A.R.’s, shear to drive reconnection. • DeVore’s ARMS code: NRL’s LCPFD FCT MHD code • Two horizontal dipoles. • Plane of symmetry ensures no shared flux • Linear shear profile: • Reconnection via num. diffusion, so only two levels of grid refinement.

11. Easier said than done! • 1st run: Reconnection not seen! Lacked sufficient topological complexity? • 2nd run, four dipoles, w/nulls & bald patch: reconnected well! dips/ helical field lines – but contrived config.

12. 3rd, 4th runs: weak reconnection • RealisticBC: six dipoles required • For untwisted runs, H > 0 state results.(*) • Tilt, after Joy’s Law, helps reconnection. (*) • Twisting fields prior to shearing enhances reconnection. (*) (Resulting H unclear!)

13. Added background field, : • Without : • reconnection occurs higher up • reconnected field exits top of box • Might keep flux systems separate when twisting (prior to shearing). (*)

14. Added converging flow to shear:

15. Evolution of :

16. Results: • Reconnected fields not prom-like: no dips, helices • Sigmoids of both types, N & S. Handedness of higher sigmoids does not correspond to SXT sigmoids.

17. Conclusions: • Topological complexity needed for reconnection! • Prominence-like configs not yet found! • Role of twist present in pre-sheared fields still under investigation.

18. References: ApJ, v. 539, 954-963, “Dynamical Formation and Stability of Helical Prominence Magnetic Fields ", DeVore, C. R. and Antiochos, S. K. (2000) ApJ, v. 553, L85-L88, "Are Magnetic Dips Necessary for Prominence Formation?", Karpen, J. T., et al. (2001) ApJ, v. 575, 578-584, "Coronal Magnetic Field Relaxation by Null-Point Reconnection,” Antiochos, S.K., Karpen, J. T., and DeVore, C.R. (2002) ApJ, v. 558, 872-887, "Origin and Evolution of Filament-Prominence Systems ,” Martens, P.C. and Zwaan, C. (2001) ApJ, v. 510, 444-459, "Formation of Solar Prominences by Flux Convergence ,” Galsgaard, K. and Longbottom, A. W. (1999)

19. Run with Joy’s Law Tilt: (*)

20. Post-reconnection topology: (*)

21. Post-twist field, prior to shearing: • Bipole systems reconnect at twisting onset. • Bipole spacing and strength might allow flux between flux systems. • Converging flow might sweep flux out of the way to allow reconnection between bipole systems. • (*)

22. H > 0 State (*)

23. Hemispheric Patterns of Chirality PhenomenonPropertyN(S) Hemisph. Filament Channel Dextral(Sinistral) Filament Barbs Right(Left)-bearing Filament X-ray Loops’ Axes CCW(CW) Rotate w/Height A.R. X-ray Loops Shape (‘sigmoid’) N(S)-shaped A.R. vector Current Helicity Neg. (Pos.) Magnetograms Magnetic Clouds Twist Left(Right)-Handed

24. VAULT II Filament Image, w/axes (courtesy, A. Vourlidas)