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

Context Ulysses: Open solar flux is ~8 x 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

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

Overview Some definitions Signatures of open field lines Synopsis and summary

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

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

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

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

Signatures of Open Fields 1.Morphology of coronal rays and loops 2.Coronal holes and voids 3.Extrapolations of photospheric magnetic fields 4.Type III metric radio bursts

Eclipse Morphology – 1950s Mustel 1963 in The Solar Corona, IAU Symp. 16, p. 331 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

Eclipse Morphology Today

EUV Morphology – 1970s Bohlin & Sheeley 1978, SolPhys 56, 125 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 Fe XV negative Mg IX negative Mag

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

Coronal Holes in ARs – 1970s Harvey & Sheeley 1979, SpSciRev 23, 139 (27-29 April 1978 NSO Å images) X-ray and 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

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

Coronal Holes in ARs Today Much improved 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

Field Line Extrapolations: 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 Harvey 1967 extensions to Schmidt program Aug. 1959

Field Line Extrapolations: 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

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)

Field Line Extrapolations: last decade Selected Observational Advances High cadence magnetograms (MDI, GONG) Snapshot synoptic maps (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.)

Field Line Extrapolations: last decade Selected Results: Open Field Lines from Active Regions IPS mapping to 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 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)

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)

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 Open Questions What is the role of transients? Where does the rest of the OF originate?

(Paesold et al A&A 371, 333) Type III radio bursts probably originate in ARs

(Wang & Sheeley 2002, JGR 107, A10, SSH 10-1) max rooted in small, low-latitude CHs near ARs

(Neugebauer et al., 2002, JGR 107, A12, SSH 13-1) max often rooted in low-latitude strong field regions ACE and Ulysses OF mappings

(Wang & Sheeley 2003, ApJ 587, max, slow SW comes from AR areas with large expansion factors Cyan = large expansion factor

(Schrijver & DeRosa 2003, SolPhys 212, 165) OF from AR min to max

AR outflow in Ne VIII matches OF (NLFF model) (Marsch et al. 2004, A&A 428, 629)

(Liewer et al. 2004, SolPhys 223, 209) Some OF traced to max (CR 1957)

(Liewer et al. 2004, SolPhys 223, 209) Some OF traced to max (CR 1957)

(Liewer et al. 2004, SolPhys 223, 209) OF not always dark in EUV (AR 8798)