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Resolving Azimuth Ambiguity Using Vertical Nature of Solar Quiet-Sun Magnetic Fields  

Sanjay Gusain   Submitted: 2012-10-24 15:04

The measurement of solar magnetic fields using the Zeeman effect diagnostics has a fundamental 180◦ ambiguity in the determination of the azimuth angle of the transverse field component. There are several methods that are used in the community and each one has its merits and demerits. Here we present a disambiguation idea that is based on the assumption that most of the magnetic field on the sun is predominantly vertical. While the method is not applicable to penumbra or other features harboring predominantly horizontal fields like the sheared neutral lines, it is useful for regions where fields are predominantly vertical like network and plage areas. The method is tested with the full-disk solar vector magnetograms observed by the VSM/SOLIS instrument. We find that statistically about 60?85 % of the pixels in a typical full-disk magnetogram has field inclination in the range of 0◦?30◦ with respect to the local solar normal, and thus can be successfully disambiguated by the proposed method. Due to its non-iterative nature, the present method is extremely fast and therefore can be used as a good initial guess for iterative schemes like nonpotential field computation (NPFC) method. Furthermore, the method is insensitive to noisy pixels as it does not depend upon the neighboring pixels or derivatives.

Authors: Sanjay Gosain and Alexei A. Pevtsov
Projects: National Solar Observatory (Sac Peak)

Publication Status: Accepted in Solar Physics
Last Modified: 2012-10-26 14:54
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A MULTI-SPACECRAFT VIEW OF A GIANT FILAMENT ERUPTION DURING 26/27 SEPTEMBER 2009  

Sanjay Gusain   Submitted: 2012-10-24 15:01

27 September 2009. The filament eruption was associated with a relatively slow coronal mass ejection (CME). The filament consisted of a large and a small part, both parts erupted nearly simultane- ously. Here we focus on the eruption associated with the larger part of the filament. The STEREO satellites were separated by about 117◦ during this event, so we additionally used SoHO/EIT and CORONAS/TESIS observations as a third eye (Earth view) to aid our measurements. We measure the plane-of-sky tra jectory of the filament as seen from STEREO-A and TESIS view-points. Us- ing a simple trigonometric relation, we then use these measurements to estimate the true direction of propagation of the filament which allows us to derive the true R/R⊙-time profile of the filament apex. Furthermore, we develop a new tomographic method that can potentially provide a more robust three-dimensional reconstruction by exploiting multiple simultaneous views. We apply this method also to investigate the 3D evolution of the top part of filament. We expect this method to be useful when SDO and STEREO observations are combined. We then analyze the kinematics of the eruptive filament during its rapid acceleration phase by fitting different functional forms to the height-time data derived from the two methods. We find that, for both methods, an exponential function fits the rise profile of the filament slightly better than parabolic or cubic functions. Finally, we confront these results with the predictions of theoretical eruption models.

Authors: Sanjay Gosain, Brigitte Schmieder, Guy Artzner, Sergei Bogachev, and Tibor Torok
Projects: CORONAS-F,SoHO-EIT,SoHO-MDI,STEREO

Publication Status: Accepted in ApJ
Last Modified: 2012-10-26 15:38
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DUAL TRIGGER OF TRANSVERSE OSCILLATIONS IN A PROMINENCE BY EUV FAST AND SLOW CORONAL WAVES: SDO/AIA AND STEREO/EUVI OBSERVATIONS  

Sanjay Gusain   Submitted: 2012-10-24 14:58

We analyze flare-associated transverse oscillations in a quiescent solar prominence on 8-9 September, 2010. Both the flaring active region and the prominence were located near the West limb, with a favorable configuration and viewing angle. The fulldisk extreme ultraviolet (EUV) images of the Sun obtained with high spatial and temporal resolution by the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory, show flare-associated lateral oscillations of the prominence sheet. The STEREO-A spacecraft, 81.5◦ ahead of the Sun-Earth line, provides on-disk view of the flare-associated coronal disturbances. We derive the temporal profile of the lateral displacement of the prominence sheet by using the image cross-correlation technique. The displacement curve was de-trended and the residual oscillatory pattern was derived. We fit these oscillations with a damped cosine function with a variable period and find that the period is increasing. The initial oscillation period (P0 ) is ∼28.2 minutes and the damping time (τD ) ∼ 44 minutes. We confirm the presence of fast and slow EUV wave components. Using STEREO-A observations we derive a propagation speed of ∼250 km s-1 for the slow EUV wave by applying time-slice technique to the running difference images. We propose that the prominence oscillations are excited by the fast EUV wave while the increase in oscillation period of the prominence is an apparent effect, related to a phase change due to the slow EUV wave acting as a secondary trigger. We discuss implications of the dual trigger effect for coronal prominence seismology and scaling law studies of damping mechanisms.

Authors: Sanjay Gosain and Claire Foullon
Projects: National Solar Observatory (Sac Peak),SDO-AIA,STEREO

Publication Status: Accepted in ApJ
Last Modified: 2012-10-26 14:55
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Abstracts by Author
Resolving Azimuth Ambiguity Using Vertical Nature of Solar Quiet-Sun Magnetic Fields
A MULTI-SPACECRAFT VIEW OF A GIANT FILAMENT ERUPTION DURING 26/27 SEPTEMBER 2009
DUAL TRIGGER OF TRANSVERSE OSCILLATIONS IN A PROMINENCE BY EUV FAST AND SLOW CORONAL WAVES: SDO/AIA AND STEREO/EUVI OBSERVATIONS

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