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Solar Magnetized Tornadoes: Rotational Motion in a Tornado-like Prominence  

Yang Su   Submitted: 2013-12-20 06:56

Su et al. 2012 proposed a new explanation for filament formation and eruption, where filament barbs are rotating magnetic structures driven by underlying vortices on the surface. Such structures have been noticed as tornado-like prominences when they appear above the limb. They may play a key role as the source of plasma and twist in filaments. However, no observations have successfully distinguished rotational motion of the magnetic structures in tornado-like prominences from other motions such as oscillation and counter-streaming plasma flows. Here we report evidence of rotational motions in a tornado-like prominence. The spectroscopic observations in two coronal lines were obtained from a specifically designed Hinode/EIS observing program. The data revealed the existence of both cold and million-degree-hot plasma in the prominence leg, supporting the so-called ``the prominence-corona transition region''. The opposite velocities at the two sides of the prominence and their persistent time evolution, together with the periodic motions evident in SDO/AIA dark structures, indicate a rotational motion of both cold and hot plasma with a speed of ∼5 km s-1.

Authors: Yang Su, Peter G"{o}m"{o}ry, Astrid Veronig, Manuela Temmer, Tongjiang Wang, Kamalam Vanninathan, Weiqun Gan, Youping Li
Projects: Hinode/EIS,Other,SDO-AIA

Publication Status: accepted by ApJL
Last Modified: 2014-03-17 17:34
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Imaging coronal magnetic-field reconnection in a solar flare  

Yang Su   Submitted: 2013-07-24 03:51

Magnetic-field reconnection is believed to play a fundamental role in magnetized plasma systems throughout the Universe1, including planetary magnetospheres, magnetars and accretion disks around black holes. This letter present extreme ultraviolet and X-ray observations of a solar flare showing magnetic reconnection with a level of clarity not previously achieved. The multi-wavelength extreme ultraviolet observations from SDO/AIA show inflowing cool loops and newly formed, outflowing hot loops, as predicted. RHESSI X-ray spectra and images simultaneously show the appearance of plasma heated to >10 MK at the expected locations. These two data sets provide solid visual evidence of magnetic reconnection producing a solar flare, validating the basic physical mechanism of popular flare models. However, new features are also observed that need to be included in reconnection and flare studies, such as three-dimensional non-uniform, non-steady and asymmetric evolution.

Authors: Su, Y., Veronig, A. M., Holman, G. D., Dennis, B. R., Wang, T. J., Temmer, M., Gan, W. Q.
Projects: GOES X-rays ,RHESSI,SDO-AIA

Publication Status: Nature Physics (2013, in press). This is the original submitted version. The final revised version is now published online.
Last Modified: 2013-07-25 09:56
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Observations of a Two-stage Solar Eruptive Event (SEE): Evidence for Secondary Heating  

Yang Su   Submitted: 2013-01-17 09:06

We present RHESSI, SDO/AIA, SOHO/LASCO, STEREO, and GOES observations of a partially occulted solar eruptive event that occurred at the southwest limb on 2011 March 8. The GOES X-ray light curve shows two peaks separated by almost 2 hr that we interpret as two stages of a single event associated with the delayed eruption of a coronal mass ejection (CME). A hot flux rope formed during the first stage and continued expanding and rising throughout the event. The speed of the flux rope decreased from ~120 to 14 km s-1 during the decay phase of the first stage and increased again during the second stage to become the CME with a speed of ~516 km s-1. RHESSI and GOES data analyses show that the plasma temperature reached over 20 MK in the first stage, then decreased to ~10 MK and increased to 15 MK in the second stage. This event provides clear evidence for a secondary heating phase. The enhanced EUV and X-ray emission came from the high corona (~60 arcsec above the limb) in the second stage, ~40 arcsec higher than the site of the initial flare emission. STEREO-A on-disk observations indicate that the post-flare loops during this stage were of larger scale sizes and spatially distinct from those in the first stage.

Authors: Su, Y.; Dennis, B. R.; Holman, G. D.; Wang, T. J.; Chamberlin, P. C.; Savage, S.; Veronig, A.

Publication Status: ApJL, 746, L5, 2012
Last Modified: 2013-01-17 14:32
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Solar Magnetized ''Tornadoes'': Relation to Filaments  

Yang Su   Submitted: 2012-07-31 04:04

Solar magnetized "tornadoes", a phenomenon discovered in the solar atmosphere, appear as tornado-like structures in the corona but root in the photosphere. Like other solar phenomena, solar tornadoes are a feature of magnetized plasma and therefore differ distinctly from terrestrial tornadoes. Here we report the first analysis of solar "tornadoes"1. A detailed case study of two events indicates that they are rotating vertical magnetic structures probably driven by underlying vortex flows in the photosphere. They usually exist as a group and relate to filaments/prominences, another important solar phenomenon whose formation and eruption are still mysteries. Solar tornadoes may play a distinct role in the supply of mass and twists to filaments. These findings could lead to a new explanation to filament formation and eruption.

Authors: Su, Y.; Wang, T. J.; Veronig, A.; Temmer, M.; Gan, W. Q.

Publication Status: ApJL (accepted)
Last Modified: 2012-08-02 12:57
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Evidence for the Full Hard X-ray Spectral Signature of Nonuniform Ionization in a Solar Flare  

Yang Su   Submitted: 2011-03-21 13:22

The hard X-ray (HXR) emission from solar flares is observed primarily from the footpoints of flare magnetic loops, where nonthermal electrons are understood to emit thick-target bremsstrahlung as they stream from the fully-ionized hot corona to the denser, cooler, and partially ionized chromosphere. The change in the plasma ionization along the path of the electrons should result in a characteristic upward break and corresponding flattening of the X-ray spectrum with increasing energy at lower energies, and a downward break at higher energies. Due to the presence of thermal emission, the upward break usually cannot be observed. We report the first evidence for both breaks in spectra measured with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) during the GOES X1.2 class flare that happened on 31 October 2002. The RHESSI X-ray spectral analysis shows both the break-up at ~49 keV and the break-down at ~134 keV at the HXR peak time. The time evolution of both breaks also agrees with the nonuniform ionization model. Other possible explanations for the breaks are considered, but the nonuniform ionization model (NUI) provides the simplest explanation for the spectral shape and its time evolution. We find that the average column density of the fully ionized plasma changed from 2x10<sup>19</sup> cm<sup-2</sup> in the rise phase to 7x10<sup>21</sup> cm<sup>-2</sup> after the peak. This indicates that plasma in the target was heated and became ionized during the flare, in agreement with heating by the nonthermal electrons and chromospheric evaporation expected in the collisional thick-target model.

Authors: Su, Y., Holman, G. D., and Dennis, B. R.
Projects: RHESSI

Publication Status: Published in ApJ, 731:106, 2011
Last Modified: 2011-03-31 09:10
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Abstracts by Author
Solar Magnetized Tornadoes: Rotational Motion in a Tornado-like Prominence
Imaging coronal magnetic-field reconnection in a solar flare
Observations of a Two-stage Solar Eruptive Event (SEE): Evidence for Secondary Heating
Solar Magnetized ''Tornadoes'': Relation to Filaments
Evidence for the Full Hard X-ray Spectral Signature of Nonuniform Ionization in a Solar Flare

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