Apparent Solar Tornado-Like Prominences
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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 (Astrophys. J. 76, 9, 1932), who studied them over many years. Observations of tornado prominences similar to the ones seen by SDO had already been documented by Secchi (Le Soleil, 1877). 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 a prominence cavity 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.
KeywordsCoronal mass ejections, low coronal signatures Coronal mass ejections, initiation and propagation Magnetic fields, corona Coronal holes, prominences, formation and evolution Filaments
OP and SM are supported in this research under the National Aeronautics and Space Administration (NASA) grant NNX09AG27G and NSF SHINE grant 0852249. The work of MV was conducted at the Jet Propulsion Laboratory, California Institute of Technology, under a contract from NASA. We are thankful to Aram Panasenco for contributions in image processing. The SECCHI data are produced by an international consortium of the NRL, LMSAL and NASA GSFC (USA), RAL and University of Birmingham (UK), MPS (Germany), CSL (Belgium), IOTA, and IAS (France). The AIA data used here are courtesy of SDO (NASA) and the AIA consortium. The Dutch Open Telescope (DOT) is located at Observatorio del Roque de los Muchachos (ORM) on La Palma. The DOT was designed and built by Rob H. Hammerschlag. We thank the referee for interesting comments and suggestions.
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