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Apparent Solar Tornado - Like Prominences  

Olga Panasenco   Submitted: 2013-07-10 11:13

Recent high-resolution observations from the Solar Dynamics Observatory (SDO) have reawakened interest in the old and fascinating phenomenon of solar tornado-like prominences. This class of prominences was first introduced by Pettit (1932), who studied them over many years. Observations of tornado prominences similar to the ones seen by SDO had already been documented by Secchi (1877) in his famous ''Le Soleil''. High resolution and high cadence multiwavelength data obtained by SDO reveal that the tornado-like appearance of these prominences is mainly an illusion due to projection effects. We discuss two different cases where prominences on the limb might appear to have a tornado-like behavior. One case of apparent vortical motions in prominence spines and barbs arises from the (mostly) 2D counterstreaming plasma motion along the prominence spine and barbs together with oscillations along individual threads. The other case of apparent rotational motion is observed in prominence cavities and results from the 3D plasma motion along the writhed magnetic fields inside and along the prominence cavity as seen projected on the limb. Thus, the ''tornado'' impression results either from counterstreaming and oscillations or from the projection on the plane of the sky of plasma motion along magnetic field lines, rather than from a true vortical motion around an (apparent) vertical or horizontal axis. We discuss the link between tornado-like prominences, filament barbs, and photospheric vortices at their base.

Authors: Olga Panasenco, Sara Martin, Marco Velli
Projects: SDO-AIA,SDO-HMI

Publication Status: accepted for publication in Solar Physics (in press); doi:10.1007/s11207-013-0337-1
Last Modified: 2013-07-10 13:40
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Using Coronal Cells to Infer the Magnetic Field Structure and Chirality of Filament Channels  

Olga Panasenco   Submitted: 2013-06-12 13:52

Coronal cells are visible at temperatures of ~ 1.2 MK in Fe XII coronal images obtained from the Solar Dynamics Observatory (SDO) and Solar Terrestrial Relations Observatory (STEREO) spacecraft. We show that near a filament channel, the plumelike tails of these cells bend horizontally in opposite directions on the two sides of the channel like fibrils in the chromosphere. Because the cells are rooted in magnetic flux concentrations of majority polarity, these observations can be used with photospheric magnetograms to infer the direction of the horizontal field in filament channels and the chirality of the associated magnetic field. This method is similar to the procedure for inferring the direction of the magnetic field and the chirality of the fibril pattern in filament channels from Hα observations. However, the coronal cell observations are easier to use and provide clear inferences of the horizontal field direction for heights up to ~ 50 Mm into the corona.

Authors: N. R. Sheeley, Jr., S. F. Martin, O. Panasenco, H. P. Warren
Projects: SDO-AIA,STEREO

Publication Status: accepted for publication in The Astrophysical Journal
Last Modified: 2013-06-12 13:52
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The Build-up to Eruptive Solar Events Viewed as the Development of Chiral Systems  

Olga Panasenco   Submitted: 2012-12-17 23:13

When we examine the chirality or observed handedness of the chromospheric and coronal structures involved in the long-term build-up to eruptive events, we find that they evolve in very specific ways to form two and only two sets of large-scale chiral systems. Each system contains spatially separated components with both signs of chirality, the upper portion having negative (positive) chirality and the lower part possessing positive (negative) chirality. The components within a system are a filament channel (represented partially by sets of chromospheric fibrils), a filament (if present), a filament cavity, sometimes a sigmoid, and always an overlying arcade of coronal loops. When we view these components as parts of large-scale chiral systems, we more clearly see that it is not the individual components of chiral systems that erupt but rather it is the approximate upper parts of an entire evolving chiral system that erupts. We illustrate the typical pattern of build-up to eruptive solar events first without and then including the chirality in each stage of the build-up. We argue that a complete chiral system has one sign of handedness above the filament spine and the opposite handedness in the barbs and filament channel below the filament spine. If the spine has handedness, the observations favor its having the handedness of the filament cavity and coronal loops above. As the separate components of a chiral system form, we show that the system appears to maintain a balance of right-handed and left-handed features, thus preserving an initial near-zero net helicity. Each individual chiral system may produce many successive eruptive events above a single filament channel.

Authors: Sara F. Martin, Olga Panasenco, Mitchell A. Berger, Oddbjorn Engvold, Yong Lin, Alexei A. Pevtsov, Nandita Srivastava
Projects: Dutch Open Telescope

Publication Status: 2nd ATST - EAST Workshop in Solar Physics: Magnetic Fields from the Photosphere to the Corona, ASP Conference Series, Vol. 463, p.157
Last Modified: 2012-12-18 15:07
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Stereoscopic Analysis of the 31 August 2007 Prominence Eruption and Coronal Mass Ejection  

Olga Panasenco   Submitted: 2012-12-11 16:11

The spectacular prominence eruption and CME of 31 August 2007 are analyzed stereoscopically using data from NASA's twin Solar Terrestrial Relations Observatory (STEREO) spacecraft. The technique of tie pointing and triangulation (T&T) is used to reconstruct the prominence (or filament when seen on the disk) before and during the eruption. For the first time, a filament barb is reconstructed in three-dimensions, confirming that the barb connects the filament spine to the solar surface. The chirality of the filament system is determined from the barb and magnetogram and confirmed by the skew of the loops of the post-eruptive arcade relative to the polarity reversal boundary below. The T&T analysis shows that the filament rotates as it erupts in the direction expected for a filament system of the given chirality. While the prominence begins to rotate in the slow-rise phase, most of the rotation occurs during the fast-rise phase, after formation of the CME begins. The stereoscopic analysis also allows us to analyze the spatial relationships among various features of the eruption including the pre-eruptive filament, the flare ribbons, the erupting prominence, and the cavity of the coronal mass ejection (CME).We find that erupting prominence strands and the CME have different (non-radial) trajectories; we relate the trajectories to the structure of the coronal magnetic fields. The possible cause of the eruption is also discussed.

Authors: P.C. Liewer, O. Panasenco, J.R. Hall
Projects: SoHO-MDI,STEREO

Publication Status: Solar Physics, Volume 282, Issue 1, pp.201-220
Last Modified: 2012-12-18 14:57
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Origins of Rolling, Twisting and Non-Radial Propagation of Eruptive Solar Events  

Olga Panasenco   Submitted: 2012-12-08 15:27

We demonstrate that major asymmetries in erupting filaments and CMEs, namely major twists and non-radial motions are typically related to the larger-scale ambient environment around eruptive events. Our analysis of prominence eruptions observed by the STEREO, SDO and SOHO spacecraft shows that prominence spines retain, during the initial phases, the thin ribbon-like topology they had prior to the eruption. This topology allows bending, rolling, and twisting during the early phase of the eruption, but not before. The combined ascent and initial bending of the filament ribbon is non-radial in the same general direction as for the enveloping CME. However, the non-radial motion of the filament is greater than that of the CME. In considering the global magnetic environment around CMEs, as approximated by the Potential Field Source Surface (PFSS) model, we find that the non-radial propagation of both erupting filaments and associated CMEs is correlated with the presence of nearby coronal holes, which deflect the erupting plasma and embedded fields. In addition, CME and filament motions respectively are guided towards weaker field regions, namely null points existing at different heights in the overlying configuration. Due to the presence of the coronal hole, the large-scale forces acting on the CME may be asymmetric. We find that the CME propagates usually non-radially in the direction of least resistance, which is always away from the coronal hole. We demonstrate these results using both low and high latitude examples.

Authors: Olga Panasenco, Sara F. Martin, Marco Velli, Angelos Vourlidas
Projects: SDO-AIA,SDO-HMI,SoHO-EIT,SoHO-MDI,SoHO-LASCO,STEREO

Publication Status: Solar Phys. (accepted)
Last Modified: 2012-12-10 14:03
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Coronal Pseudostreamers: Source of Fast or Slow Solar Wind?  

Olga Panasenco   Submitted: 2012-12-08 15:22

We discuss observations of pseudostreamers and their 3D magnetic configuration as reconstructed with potential field source surface (PFSS) models to study their contribution to the solar wind. To understand the outflow from pseudostreamers the 3D expansion factor must be correctly estimated. Pseudostreamers may contain filament channels at their base in which case the open field lines diverge more strongly and the corresponding greater expansion factors lead to slower wind outflow, compared with pseudostreamers in which filament channels are absent. In the neighborhood of pseudostreamers the expansion factor does not increase monotonically with distance from the sun, and doesn't simply depend on the height of the pseudostreamer null point but on the entire magnetic field configuration.

Authors: Olga Panasenco, Marco Velli
Projects: SDO-AIA,SDO-HMI,SoHO-LASCO

Publication Status: Solar Wind 13: Proceedings of the Thirteenth International Solar Wind Conference (accepted)
Last Modified: 2012-12-10 14:03
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Abstracts by Author
Apparent Solar Tornado - Like Prominences
Using Coronal Cells to Infer the Magnetic Field Structure and Chirality of Filament Channels
The Build-up to Eruptive Solar Events Viewed as the Development of Chiral Systems
Stereoscopic Analysis of the 31 August 2007 Prominence Eruption and Coronal Mass Ejection
Origins of Rolling, Twisting and Non-Radial Propagation of Eruptive Solar Events
Coronal Pseudostreamers: Source of Fast or Slow Solar Wind?

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