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DYNAMICS of a SOLAR PROMINENCE TORNADO OBSERVED by SDO/AIA on 2012 NOVEMBER 7–8 Irakli Mghebrishvili1, Teimuraz V

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DYNAMICS of a SOLAR PROMINENCE TORNADO OBSERVED by SDO/AIA on 2012 NOVEMBER 7–8 Irakli Mghebrishvili1, Teimuraz V The Astrophysical Journal, 810:89 (9pp), 2015 September 10 doi:10.1088/0004-637X/810/2/89 © 2015. The American Astronomical Society. All rights reserved. DYNAMICS OF A SOLAR PROMINENCE TORNADO OBSERVED BY SDO/AIA ON 2012 NOVEMBER 7–8 Irakli Mghebrishvili1, Teimuraz V. Zaqarashvili1,2, Vasil Kukhianidze1, Giorgi Ramishvili1, Bidzina Shergelashvili1,3, Astrid Veronig4, and Stefaan Poedts3 1 Abastumani Astrophysical Observatory at Ilia State University, University St. 2, Tbilisi, Georgia; [email protected] 2 Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, A-8042 Graz, Austria 3 Centre for Mathematical Plasma Astrophysics, Celestijnenlaan 200B, B-3001 Leuven, Belgium 4 IGAM-Kanzelhöhe Observatory, Institute of Physics, University of Graz, Universitätsplatz 5, A-8010 Graz, Austria Received 2014 July 15; accepted 2015 July 30; published 2015 September 2 ABSTRACT We study the detailed dynamics of a solar prominence tornado using time series of 171, 304, 193, and 211 Å spectral lines obtained by the Solar Dynamics Observatory/Atmospheric Imaging Assembly during 2012 November 7–8. The tornado first appeared at 08:00 UT, November 07, near the surface, gradually rose upwards − with the mean speed of ∼1.5 km s 1 and persisted over 30 hr. Time–distance plots show two patterns of quasi- periodic transverse displacements of the tornado axis with periods of 40 and 50 minutes at different phases of the tornado evolution. The first pattern occurred during the rising phase and can be explained by the upward motion of the twisted tornado. The second pattern occurred during the later stage of evolution when the tornado already stopped rising and could be caused either by MHD kink waves in the tornado or by the rotation of two tornado threads around a common axis. The later hypothesis is supported by the fact that the tornado sometimes showed a double structure during the quasi-periodic phase. 211 and 193 Å spectral lines show a coronal cavity above the prominence/tornado, which started expansion at ∼13:00 UT and continuously rose above the solar limb. The tornado finally became unstable and erupted together with the corresponding prominence as coronal mass ejection (CME) at 15:00 UT, November 08. The final stage of the evolution of the cavity and the tornado-related prominence resembles the magnetic breakout model. On the other hand, the kink instability may destabilize the twisted tornado, and consequently prominence tornadoes can be used as precursors for CMEs. Key words: Sun: atmosphere – Sun: filaments, prominences – Sun: oscillations Supporting material: animations 1. INTRODUCTION Su et al. (2014) observed Doppler shifts in tornado-like prominences and showed that the tornadoes under study Solar giant tornadoes appear in the corona like a twisted rope revealed persistent redshifts and blueshifts on the opposite or a fine screw (Pettit 1925). They are usually related to filaments/prominences which are called “tornado promi- sides of the tornado axis, which means that tornadoes are ” ( ) indeed rotating structures and the rotation is not a “vortical nences Zöllner 1869; Pettit 1950 . The tornadoes are ” ( ) probably formed either due to the expansion of a twisted flux illusion Panasenco et al. 2014 . ( ) Observations show frequent small and large amplitude rope into the coronal cavity Li et al. 2012; Panesar et al. 2013 ( ) or due to large vortex flows, which are frequently observed in oscillations in solar prominences Arregui et al. 2012 . Large- ( ) amplitude oscillations are caused by Moreton waves (Ramsey the solar photosphere Brandt et al. 1988; Attie et al. 2009 . ) ( ) Recent observations also showed the existence of small scale & Smith 1966 , EIT waves Okamoto et al. 2004 , nearby fl ( š ) fl tornadoes (magnetic tornadoes) in the chromosphere, which sub ares Jing et al. 2003;Vrnak et al. 2007 , or local ux fi ( ) may provide an alternative mechanism for channeling energy emergence near the laments Isobe & Triphati 2006 . In some from the lower into the upper solar atmosphere (Wedemeyer- cases, the oscillations are associated to the eruptive phase of a fi ( ) Böhm et al. 2012). The small scale tornadoes are probably lament Isobe & Triphati 2006; Isobe et al. 2007 . On the formed by small scale photospheric vortex flows, which are other hand, small-amplitude oscillations have no particular frequently observed and also frequently occur in numerical triggering sources and they are frequently observed in solar simulations (Stein & Nordlund 1998; Bonet et al. 2008, 2010; prominence threads (Oliver & Ballester 2002; Lin et al. 2005, Wedemeyer-Böhm & Rouppe van der Voort 2009; Steiner 2007, 2009; Mackay et al. 2010). As giant tornadoes are et al. 2010). generally associated with prominences/filaments, they may Solar prominences are large magnetic structures confining also show some sort of oscillatory motions. cool and dense plasma in the hot solar corona. They may Quiescent prominences are often surrounded by coronal persist from a few days to several months. Prominences/ cavities, which appear as dark semicircular or circular regions filaments may undergo large-scale instabilities which may lead in the corona. Coronal cavities and prominences may erupt to their eruption. These eruptions are often associated with together as CMEs. Consequently, cavities are often observed in flares and coronal mass ejections (CMEs; Labrosse et al. 2010; CMEs with three-part structure (Illing & Hundhausen 1985; Mackay et al. 2010). Solar tornadoes, which are associated with Chen et al. 1997; Dere et al. 1999). Therefore, to study the prominences, can erupt together with the filament spine (Su relation between giant tornadoes and coronal cavities is an et al. 2012; Wedemeyer-Böhm et al. 2013). Tornadoes may interesting problem. Giant tornadoes might be related to the play a distinct role in the supply of mass and twists to filaments destabilization of prominences/filaments and the consequent (Su et al. 2012). Recently Wedemeyer-Böhm et al. (2013) and initiation of CMEs, therefore studies of their evolution is 1 The Astrophysical Journal, 810:89 (9pp), 2015 September 10 Mghebrishvili et al. relevant for solar and space weather predictions. In this paper characteristic for tornados (Su et al. 2012; Wedemeyer-Böhm we present a case study of the formation, evolution and et al. 2013). eruption of a solar giant tornado observed by the Atmospheric Imaging Assembly (AIA)/Solar Dynamics Observatory (SDO). 3. RESULTS In order to study in detail the temporal dynamics of the tornado, we constructed time–distance plots at six different 2. OBSERVATIONS AND DATA ANALYSIS height levels above the limb. The location of these six cuts is We use observational data obtained by the AIA (Lemen shown on middle right panel of Figure 1 by white solid lines. et al. 2012) on board the SDO (Pesnell et al. 2012) on 2012 The first cut (indicated by 1) is located at the height of November 7–8. AIA provides full disk observations of the Sun ∼14 Mm and the sixth cut (indicated by 6) is located at a height in three ultraviolet continua and seven EUV narrow band of ∼44 Mm above the solar limb. The distance between each of channels with 1″. 0 resolution and 12 s cadence. We use level the five lines from cut 2 to cut 6 is 2.9 Mm. 1.0 images of the 171, 304, 193, and 211 Å band channels. The Figure 2 shows the time–distance diagram at the cut 1 (upper level 1.0 images include the bad-pixel removal, despiking and panel) and the cut 6 (lower panel) during its full lifetime from flat-fielding. The data are calibrated and analyzed using 05:00 UT, 2012 November 07, to 15:00 UT, 08 November. On standard routines in the SolarSoft (SSW) package. the lower panel it is seen how the tornado appeared at the The event has been observed from 08:00 UT, 2012 height of the cut 6 (∼44 Mm) near 17:00 UT, November 07. November 07, to 15:30 UT, November 08. The time series There are apparent quasi-periodic transverse displacements of shows that the tornado started to form at 08:00 UT on 2012 the axis during different intervals during its lifetime. We select November 07 on the solar southwest limb and persisted over and study two clear patterns, which are presented in selected ∼30 hr. The tornado was associated with a solar prominence, areas on Figure 2. which eventually erupted as a CME. Figure 1 shows the Figure 3 shows the zoom of the white box on the upper panel formation and evolution of the tornado in the 171 Å filter of Figure 2. The clear quasi-periodic pattern starts at 14:00 UT, during the whole life-time. Tornadoes are usually visible as a November 7, when the tornado actually formed, and persists dark absorption structure in the 171 Å filter, but they may for 7 hr. The period and amplitude of the periodic displacement appear as emitting structures in the 304 Å filter (Wedemeyer- are gradually increasing with time, but the pattern disappears Böhm et al. 2013). The top-left panel shows the coronal image later. The period is initially about 40 minutes, but increases up at 15:01 UT, November 06, where the tornado was not yet to 100 minutes at the end. seen. The white arrow indicates the place where the tornado Figure 4 (upper panel) shows the zoom of the white box on was formed later. The top-right panel shows the tornado at the lower panel of Figure 2. The five panels of the figure reveal 09:25 UT, November 07, in the form of a thin black thread (the the dynamics of the tornado at the heights corresponding to five corresponding image in the 304 Å line is shown on upper left upper cuts shown in Figure 1.
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