The CME Link to Filaments and Filament Channels

1. The CME Link to Filaments and Filament Channels Sara F. Martin, Olga Panasenco Helio Research La Crescenta, CA, USA Oddbjorn Engvold and Yong Lin Institute for Theoretical Astrophysics University of Oslo, Oslo, Norway

2. Abstract We present a broad concept for the build-up to eruptive solar events that needs to be tested in future observational and theoretical research. In this concept, eruptive solar events are a magnetic system consisting of a coronal mass ejection originating from coronal loops, a filament eruption originating from a filament magnetic field separate from the magnetic field of the overlying loops, a cavity with an invisible magnetic field in the space between the coronal field and the filament field, and a flare whose occurrence depends on the rising of the magnetic fields of the other components. Our rationale for this systems concept is showing that the associations between these components of eruptive systems are much higher than statistics have yet shown from H images. Verification of such a systems concept is important to understanding that the initial energy source must be external to the eruptive system but also feed into it. The clues to the source of energy are found in the build-up of filament channels closely related to observed canceling magnetic fields along polarity reversal boundaries common to all eruptive solar events. Continued on next page

3. The building a filament channel is a necessary condition to providing a conduit for the transfer of magnetic flux from the photosphere into the corona. When the filament channel is completely developed, i.e., has reached the condition of maximum magnetic shear along a polarity reversal boundary, the transfer of magnetic flux associated with the observed canceling magnetic fields then maintains the channel while an excess of flux provided by this process goes into building a filament magnetic field. Concurrently the transfer of flux carries bits of flowing plasma into the corona that we call a filament when its density becomes high enough to be visible against the solar disk. The transfer of flux is a non reversible process forcing the continuous build-up of a filament magnetic field. However, the mass being transferred continuously into the filament field also slowly drains out leaving invisible filament magnetic field in the corona which then becomes a major part of the cavity magnetic field. When the build up of magnetic pressure in the filament and cavity magnetic fields exceeds that of the overlying coronal loops, the whole solar eruptive event has an early beginning as an observable slow rise which can last a few hours to many days before rapid onset and ejection of the eruptive magnetic system. We suggest that this process can be accelerated by any number of external triggering mechanisms that serve as catalysts to cause the impending eruption to happen earlier than it otherwise would occur.

4. Components of Eruptive Solar Events Cavity

5. In the following slides, we illustrate why current statistics on the percentage associations of erupting filaments with CMEs of about 75-80% are minimum values. We provide evidence that a much higher percentage of associations would be found if the statistics on filaments could be based on Helium I and Helium II images in addition to Ha.

6. Prominences in some cases appear earlier in 304 than in Ha. BBSO Ha 5/22/02 BBSO Ha 5/24/02 EIT 304A 5/25/02 BBSO Ha 6/16/02 EIT 304A 5/25/02 In 304 A, a spinejoins the spines of two filaments that appear to be separate in Ha

7. The spines of quiescent prominences in He II 304A are often longer and slightly taller than in Ha images.

8. During eruption, faint parts of prominences in He II 304A are much more easily recorded than in Ha .

9. The next two slides illustrate that the association of flares with erupting filaments would be much higher if the statistical association were based on Helium I and Helium II images in addition to Ha. The next slide is a comparison of an erupting filament and flare observed concurrently in the D3 line of He I (upper row) and in Ha (lower row). The filament, plage, and flare are all seen in absorption in the He I, D3 line but are co-spatial with their Ha counterparts. It is seen that the dark flare ribbons in He I are significantly longer and slightly broader than in Ha. Observations and illustrations were acquired by Harry Ramsey at the former Lockheed Solar Observatory.

10. For more detail, see next page Comparison of an erupting filament and flare observed concurrently in the D3 line of He I (upper row) and in Ha (lower row). The filament, plage, and flare are all seen in absorption in the He I, D3 line but are co-spatial with their Ha counterparts. It is seen that the dark flare ribbons in He I are significantly longer and slightly broader than in Ha. Observations and illustrations were acquired by Harry Ramsey at the former Lockheed Solar Observatory.

12. The core of He I D3 flares in active regions, where the magnetic flux density is high, can be in emission early in the development of a flare. The changing absorption is either the flare ribbons or flare loops while the non-changing absorbing features are sunspots. Enlarged in next slide Some flares on the quiet Sun are visible only as absorbing ribbons in the He I line at 10830 are seen only weakly as emission in Ha or are not seen at all in Ha. Hence He statistical associations of flares to erupting filaments would be much higher if He I images were available for statistical studies.

14. We have illustrated that a higher correspondence between CME , erupting filaments and flares should be very high if statistical associations between them could be based on He I and He II images in addition to Ha images. Hence we make the following hypthesis. Cavity Hypothesis: (a) The CME, Flare, Cavity and Erupting Filament are all parts of a single eruptive magnetic system and therefore (b) their common cause or driver is external to the system.

15. Question:What do CMEs, Erupting Filaments, Cavities and Flares all have in common? Answers: General: a polarity reversal boundary between opposite polarity magnetic fields (polarity reversal boundary = neutral line = polarity inversion) But more specifically:a polarity reversal boundary that is also a filament channel And most specifically:a “fully-developed” filament channel (one with maximum magnetic shear - ready for filament formation)

16. Next questions: (1) What is a filament channel? (2) What are the characteristics of a “fully-developed” filament channel?

17. A filament channel is loosely defined as volume of space around a polarity reversal boundary characterized by the specific properties (1) A path of fibrils aligned along the polarity reversal boundary (2)No fibril crossing the polarity reversal boundary

18. (1) An example of fibrils aligned along the polarity reversal boundary The white line identifies the polarity reversal boundary. From the direction of the fibrils, we can infer a vector magnetic field component aligned with the fibrils and polarity boundary

19. The polarity reversal boundary is sometimes a zone rather a line.

20. (2) The fully-developed condition of filament channels occurs when fibrils no longer cross the polarity reversal boundary = The chromospheric condition for filament formation is fulfilled = no magnetic field lines from active region or network magnetic fields cross the polarity boundary (the zone of maximum magnetic shear).

21. Magnetic Field Configuration of a Filament Channel From the photospheric polarity boundary to the top of the filament spine,the channel has a magnetic field configuration like a tangential discontinuity such as in the solar wind. Across the polarity boundary, the magnetic field gradually changes in direction from vertically outward on one side, to horizontal along the polarity boundary and then to inward on the other side of the polarity boundary. This pattern is indicated in the fibril structure of filament channels.

22. Example of an empty filament channel (no filament) and a filament channel partially occupied by a filament

23. The physical significance of filament channels: • The channel magnetic field deviates more from a potential field configuration than most other locations on the Sun. • Therefore filament channels represent locations on the Sun where energy is being stored. • The evolution of filament channels shows evidence of their accumulated energy is in the photosphere, chromosphere and low corona. (as revealed in photospheric vector magnetograms, Ha fibrils, and coronal structure (EIT 171A and 195A)).

24. Continuation of: • The physical significance of filament channels: • However the photospheric and chromospheric parts of the channel reveal little evidence of changing configuration (giving-up energy) during a CME. • Therefore we deduce that the coronal part of the channel is the primary site where the energy is stored and later released during eruptive solar event.

25. The big question:How do the coronal parts of the filament channel store energy? * The only change observed beneath all CMEs, filaments and flares are canceling magnetic fields in the photospheric part of the channel.

26. Magnetic reconnection near the photo-sphere accounts for canceling magnetic fields and the concurrent formation of filament magnetic fields (Litvinenko 1999; Litvinenko and Martin 1999; Wood and Martens 2003; and Litvinenko, Chae and Park 2007).

27. Five Key Points: • (1) In our view the canceling magnetic fields represent magnetic reconnection at or near the photosphere - a process by which line-of-sight magnetic field is extracted from the photosphere and stored first in the fibril fields of the chromosphere.

28. 2nd of Three Key Points: • (2) When the condition of maximum magnetic shear is reached in a filament channel, the line-of-sight canceling magnetic fields are converted slowly to transverse filament magnetic fields in the low corona along polarity boundaries.

29. 3rd of Three Key Points: • (3) Magnetic reconnection, associated with canceling magnetic fields, converts short field lines into longer field lines (van Ballegooijen and Martens (1989), Martens and Zwaan (2001). An open question has been at height this magnetic reconnection occurs. Because there is a notable lack of brightenings in quiescent filament channels, and channels intermediate between quiet Sun channels and active region channels, we suggest that the reconnection that accounts for cancelling fields, filament channel and filament formation must take place in dense plasma near the photosphere.

30. 4th of Five Key Points • In this scenario, a lot of the filament magnetic field can exist without field aligned mass. If the mass input exceeds the outflow, a filament gradually becomes visible as threads of flowing mass (Engvold 1988; Zirker 1989; Gaizauskas, Zirker, Sweetland, Kovacs 1997)

31. 5th of Five Key Points • Filament magnetic fields are nearly always growing -they increase as long as canceling magnetic fields are present along all fully-developed filament channel. • The cancellation can stop and the process of filament formation can cease but throughout most of the solar cycle, the long slow building of filament channels and filaments is a major driving force locally pushing overlying coronal fields outward until the more explosive coronal reconnection results in the CME, erupting filament, and solar flare.

32. SUMMARY: 7. CME + Erupting Filament + Cavity + Flare 6. Expanding coronal loop system 5. Outward pressure on overlying corona 4. Filament Magnetic Field Formation 3. Filament Channel Formation 2. Photospheric magnetic reconnection 1. Solar convection + Active region evolution

33. Acknowledgments O. Panasenco and S.F. Martin acknowledge support for preparing this paper to NSF grant 0519249.

34. References Engvold, O. 1988, in Priest (ed.) Dynamics and Structure of Solar Prominences, Kluwer Academic Publishers, Dordrecht, p. 47 Gaizauskas, V., Zirker, J.B., Sweetland, C. and Kovacs, A. 1997, Astrophys. J. 479, 448 Litvinenko, Y. 1999, Astrophys. J. 515, 435 Litvinenko, Y. and Martin, S.F., 1999 Solar Phys. 190, 45-58 Litvinenko, Yuri E., Chae, Jongchul, and Park, So-Young 2007, Astrophys. J. 662, 1302-1308 Martens, P.C.H. and Zwaan, C. 2001, Astrophys. 558, 872-887 Martin, S.F. 1986, in A. Poland (ed.) Coronal and Prominence Plasmas, NASA Conference Publ. 3224, p. 73 van Ballegooijen, A.A. and Martens, P.C.H. 1989, Astrophys. J. 343, 971 Zirker, J.B.1989, Solar Phys. 119, 341