1 / 24

What is the Evidence for Open Field Lines from Active Regions?

What is the Evidence for Open Field Lines from Active Regions?. J. Harvey National Solar Observatory. Context. Ulysses : Open solar flux is ~8 x 10 22 Mx with little latitude or time dependence at ≥ 1 AU (small variance is a hot topic) How much of it comes from: Coronal holes Streamers

nigel
Download Presentation

What is the Evidence for Open Field Lines from Active Regions?

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. What is the Evidence for Open Field Lines from Active Regions? J. Harvey National Solar Observatory

  2. Context • Ulysses: Open solar flux is ~8 x 1022 Mx with little latitude or time dependence at ≥ 1 AU (small variance is a hot topic) • How much of it comes from: • Coronal holes • Streamers • Quiet sun • Active regions

  3. Scope • Marcia’s talk addresses solar wind properties associated with supposed open field lines from active regions • I consider near-Sun observational evidence for open fields in active regions • Transients mostly ignored

  4. Overview • Some definitions • Signatures of open field lines • Synopsis and summary

  5. Abbreviations OF = open field AR = active region CH = coronal hole SW = solar wind PFSS = potential field source surface

  6. Open Field Lines • Field lines that start in photosphere and “end” in interplanetary space • Conduits for plasma to move inward or outward from or to the solar wind • Field lines that reach β > 1 regime • Field lines cannot be directly observed

  7. Active Region The entire time-varying structure produced by emergence of a sunspot-producing magnetic flux rope.

  8. Open Fields from ARs? • Presumption of open field lines from ARs is long-standing (Maunder, Birkeland, etc.) • No direct evidence from remote sensing • Conjecture

  9. Signatures of Open Fields • Morphology of coronal rays and loops • Coronal holes and voids • Extrapolations of photospheric magnetic fields • Type III metric radio bursts

  10. Eclipse Morphology – 1950s • Based on Russian studies of many total eclipse photos • Long, narrow rays often seen over “centers of activity” (i.e. ARs) • Presumption of “corpuscular streams” from ARs • Implies some (weak) evidence for open field lines from ARs Mustel 1963 in The Solar Corona, IAU Symp. 16, p. 331

  11. Eclipse Morphology Today

  12. EUV Morphology – 1970s • X-ray and EUV AR images from space show dark voids, loop “fountains” and sprays • Interpreted as miniature active region coronal holes • Contain relatively large amounts of magnetic flux, comparable to large coronal holes • Implies ~10% of flux of the AR is open Mag Fe XV negative Mg IX negative Bohlin & Sheeley 1978, SolPhys 56, 125

  13. SOLIS/VSM chromospheric magnetogram 12 Nov 2006 EUV Morphology Today XRT/Hinode temperature image 12 Nov 2006 (XRT POW 2007 June 7 by F. Reale and S. Parenti)

  14. Coronal Holes in ARs – 1970s Harvey & Sheeley 1979, SpSciRev 23, 139 (27-29 April 1978 NSO 10830 Å images) • X-ray and 10830 Å images showed transient CHs adjacent to ARs • Last up to 1 day after flare • Associated with high-speed winds • Interpreted as high-reaching closed field lines opened as a result of a flare or CME • aka coronal voids, dimmings, depletions

  15. Coronal Holes in ARs – 1980s 1826 UT B|| 2106 UT Δt 1982 Dec 17, X10 and M4 flares 10830 Å KPVT Recely & Harvey 1986, in Solar-Terrestrial Predictions, Meudon, P. A. Simon et al, p. 204

  16. Coronal Holes in ARs Today • Much improved 10830 Å observations(de Toma, Holzer, Burkepile, Gilbert 2005, ApJ 621, 1109) • Far better EUV and X-ray observations (e.g., EIT: Attrill et al. 2006, SolPhys 238, 117) • Large and growing literature • But, most coronal dimming studies concentrate on events adjacent to ARs not deep inside ARs

  17. Field Line Extrapolations: 1967-1970 Aug. 1959 Harvey 1967 extensions to Schmidt program • No source surface or no plotted field lines with source surface • Poor spatial and time resolution • Poor field measurements • Minimal physics • “Unipolar magnetic regions … result in open field lines …” (Schatten 1968, Nature 220, 1211) Newkirk, Altschuler, Harvey 1968, IAU Symp. 35, 379

  18. Field Line Extrapolations: 1970-1982 • Advances • Potential field with source surface • Some non-potential experiments • Better spatial resolution (~ x100) • Better field measurements • Still minimal physics (Pneuman, Hansen & Hansen 1978, SoPhy 59, 313) • Selected findings • Open fields inferred from ARs • Strong cycle variation of AR open fields (at max most traceable to ARs; almost none at min) Randy Levine, ca. 2004

  19. Field Line Extrapolations: last decade • Selected Modeling Advances • PFSS and MHD model extrapolations of open FL footpoints compare well (Neugebauer et al. 1998, JGR 103, 14587) • Interchange reconnection model (Fisk, Schwadron & Zurbuchen 1999, JGR 104, 19765; see also Marsh 1978, SolPhys 59, 105) • High-resolution “local” PFSS models (e.g. Marsch, Wiegelmann & Xia 2004, A&A 428, 629) • Resolution of PFSS models has “tremendous” influence on open field footpoint locations (Poduval & Zhao 2004, JGR 109, A08102) • “Open Flux Equilibrium” model (Gilbert, Zurbuchen & Fisk 2007, ApJ 663, 583) • Strict CH topology for PFSS and MHD quasi-steady models (Antiochos et al. 2007, ApJ submitted)

  20. Field Line Extrapolations: last decade • Selected Observational Advances • High cadence magnetograms 1996- (MDI, GONG) • Snapshot synoptic maps 1998- (Worden & Harvey; Schrijver & DeRosa) • Better calibrations (e.g. old KPVT archive) • Polar field treatment • Regular chromospheric LOS and photospheric vector FD data • PFSS models run in near real time (e.g. NOAA, Lockheed, NSO, etc.)

  21. Field Line Extrapolations: last decade • Selected Results: Open Field Lines from Active Regions • IPS mapping to ARs @ min show slow wind from one side (Kojima et al. 1998, JGR 104, 16993) • Type III radio bursts probably originate in ARs (Paesold et al. 2001 A&A 371, 333) • OF at max rooted in small, low-latitude CHs near ARs (Wang & Sheeley 2002, JGR 107, A10, SSH 10-1) • OF at max often rooted in low-latitude strong field regions (Neugebauer et al., 2002, JGR 107, A12, SSH 13-1)

  22. Field Line Extrapolations: last decade • Selected Results: Open Field Lines from Active Regions • At max, slow SW comes from AR areas with large expansion factors (Wang & Sheeley 2003, ApJ 587, 818) • OF from AR <1% at min to 30-50% at max (Schrijver & DeRosa 2003, SolPhys 212, 165) • FL from emerging AR may reconnect with CH FL to open AR FL (Neugebaur & Liewer 2003, JGR 108, A1 SSH3-1) • AR outflow in Ne VIII matches OF (Marsch et al. 2004, A&A 428, 629) • Some OF traced to AR at max; not always dark in EUV (Liewer et al. 2004, SolPhys 223, 209)

  23. Synopsis and Summary • Compelling (indirect) evidence for open field lines from active regions – even some sunspots • Expected whenever an AR emerges in an area dominated by one polarity • As much as 10% of AR flux may be open • Strong cycle variation: <1% at min to ~50% at max • Better field measurements needed in sunspots • OpenQuestions • What is the role of transients? • Where does the rest of the OF originate?

More Related