1 / 24

Flux Collision Models of Prominence Formation

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). Essentials of prominence field:. Sheared field parallel to PIL.

tynice
Télécharger la présentation

Flux Collision Models of Prominence Formation

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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)

More Related