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Revision of Solar Spicule Classification  

Yuzong Zhang   Submitted: 2012-02-20 22:11

Solar spicules are the fundamental magnetic structures in thechromosphereand considered to play a key role in channeling the chromosphere andcorona.Recently, it was suggested by De Pontieu et al. that there were twotypes ofspicules with very different dynamic properties, which were detectedby space-time plot technique in the Ca II H line (3968A) wavelength fromHinode/SOTobservations. 'Type I' spicule, with a 3-7 minute lifetime, undergoesa cycle ofupward and downward motion; in contrast, 'Type II' spicule fades awaywithindozens of seconds, without descending phase. We are motivated by thefact thatfor a spicule with complicated 3D motion, the space-time plot, whichis madethrough a slit on a fixed position, could not match the spiculebehavior all thetime and might lose its real life story. By revisiting the same datasets, weidentify and trace 105 and 102 spicules in quiet sun (QS) and coronalhole (CH),respectively, and obtain their statistical dynamic properties. First,we have notfound a single convincing example of 'Type II' spicules. Secondly,more than60% of the identified spicules in each region show a complete cycle,i.e., majorityspicules are 'Type I'. Thirdly, the lifetime of spicules in QS and CHare 148 sand 112 s, respectively, but there is no fundamental lifetimedifference betweenthe spicules in QS and CH reported earlier. Therefore, the suggestionof coronalheating by 'Type II' spicules should be taken with cautions.

Authors: Y. Z. Zhang, K. Shibata, J. X. Wang, X. J. Mao, T. Matsumoto, Y. Liu, and J. T. Su
Projects: Hinode/SOT

Publication Status: Accepted by ApJ on Feb 18, 2012
Last Modified: 2012-02-21 10:24
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Propagation of Moreton Waves  

Yuzong Zhang   Submitted: 2011-04-08 02:57

With FMT and SMART telescopes at Hida Observatory of Kyoto University,13 events of Moreton waves were captured at Hα center,±0.5 Å and ±0.8 Å wavebands since 1997. Withsuch samples, we have studied the statistical properties of thepropagation of Moreton waves. Moreton waves were all restricted insectorial zones with the mean value of 92°. However, theiraccompanied EIT waves, observed simultaneously with SOHO/EIT atExtreme-ultraviolet wavelength, were much isotropic with quiteextended scope of 193°. The average propagation speed of theMoreton waves and the corresponding EIT waves were 664 kms-1 and 205 km s-1, respectively. Moreton waveswere propagating either under the large-scale close magnetic fluxloops, or firstly in the sectorial region where two sets of magneticloops separated each other and diverged, and then stopped before theopen magnetic flux region. The location swept by Moreton waves hadrelatively weak magnetic field compared to the magnetic fields attheir sidewalls. The ratio of magnetic flux density between thesidewalls and path falls in the range of 1.4 to 3.7 at the height of0.01 solar radii. Additionally, we roughly estimated the distributionof fast magnetosonic speed between the propagating path and sidewallsin an event on 1997 November 3, and found the relatively low fastmagnetosonic speed in the path. We also found that the propagatingdirection of Moreton waves coincided with the direction of filamenteruption in a few well-observed events. This favors an interpretationof 'Piston' model, although further studies are necessary fordefinitive conclusion.

Authors: Y.Z. Zhang, R. Kitai, N. Narukage, T. Matsumoto, S. Ueno, K. Shibata and J.X. Wang
Projects: None

Publication Status: PASJ (in press)
Last Modified: 2011-04-08 08:18
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Coronal Magnetic Connectivity and EUV Dimmings  

Yuzong Zhang   Submitted: 2007-03-20 03:50

Coronal dimming can be considered to be a disk signature of front-side coronal mass ejections (CMEs) (Thompson et al., 2000, Geophys. Res. Lett. 27, 1431). The study of the magnetic connectivity associated with coronal dimming can shed new light on the magnetic nature of CMEs. In this study, four major flare-CME events on July 14 2000, October 28 2003, November 7 2004, and January 15 2005 are analyzed. They were all halo CMEs associated with major flare activity in complex active regions (ARs), and produced severe space weather consequences. To explore the magnetic connectivity of these CMEs, global potential-field extrapolations based on the composite synoptic magnetograms from the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory (SOHO) are constructed, and their association with coronal dimming revealed by the Extreme ultra-violet Imaging Telescope (EIT) is studied. It is found that each flare-CME event involved interaction of more than ten sets of magnetic-loop systems. These loop systems occupied over 50% of all identified loop systems in the visible hemisphere and covered a wide range of solar longitudes and latitudes. We categorize the loop systems as active-region loops (ARLs), AR-interconnecting loops (ARILs) including trans-equatorial loops (TLs), and long arcades (LAs) straddling filament channels. A recurring pattern, the saddle-field configuration (SFC) consisting of ARILs, is found to be present in all four major flare-CME events. The magnetic connectivity revealed by this work implies that inter-coupling and interaction of multiple flux-loop systems are required for a major CME. For comparison, a simple flare-CME event of 12 May 1997 with a relatively simple magnetic configuration is chosen. Even for this simple flare-CME event, we find that multiple flux-loop systems are also present.

Authors: Yuzong Zhang, Jingxiu Wang, Gemma D. R. Attrill, Louise K. Harra, Zhiliang Yang, Xiangtao He
Projects: None

Publication Status: accepted by Sol. Phys.
Last Modified: 2007-03-20 09:17
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Revision of Solar Spicule Classification
Propagation of Moreton Waves
Coronal Magnetic Connectivity and EUV Dimmings

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