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Velocity vectors of a quiescent prominence observed by Hinode/SOT and the MSDP (Meudon)  

R. Chandra   Submitted: 2009-12-02 06:27

The dynamics of prominence fine structures is a challenge to understand the formation of cool plasma prominence embedded in the hot corona. Recent observations from the high resolution Hinode/SOT telescope allow us to compute velocities perpendicularly to the line-of-sight or transverse velocities. Combining simultaneous observations obtained in Hα with Hinode/SOT and the MSDP spectrograph operating in the Meudon solar tower we derive the velocity vectors of a quiescent prominence. The velocities perpendicular to the line-of-sight are measured by time slice technique, the Dopplershifts by the bisector method. The Dopplershifts of bright threads derived from the MSDP reach 15 km s-1 at the edges of the prominence and are between ± 5 km s-1 in the center of the prominence. Even though they are minimum values due to seeing effect, they are of the same order as the transverse velocities. These measurements are very important because they suggest that the verticalstructures shown in SOT may not be real vertical magnetic structures in the sky plane. The vertical structures could be a pile up of dips in more or less horizontal magnetic field lines in a 3D perspective, as it was proposed by many MHD modelers. In our analysis we also calibrate the Hinode Hα data using MSDP observations obtained simultaneously.

Authors: Schmieder, B., Chandra, R., Berlicki, A., Mein, P.
Projects: Hinode/SOT,SoHO-MDI

Publication Status: Submitted in A & A
Last Modified: 2009-12-02 17:20
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How can a Negative Magnetic Helicity Active Region Generate a Positive Helicity Magnetic Cloud ?  

R. Chandra   Submitted: 2009-10-07 02:24

The geoeffective magnetic cloud (MC) of 20 November 2003, has been associated to the 18 November 2003, solar active events in previous studies. In some of these, it was estimated that the magnetic helicity carried by the MC had a positive sign, as well as its solar source, active region (AR) NOAA 10501. In this paper we show that the large-scale magnetic field of AR 10501 had a negative helicity sign. Since coronal mass ejections (CMEs) are one of the means by which the Sun ejects magnetic helicity excess into the interplanetary space, the signs of magnetic helicity in the AR and MC should agree. Therefore, this finding contradicts what is expected from magnetic helicity conservation. However, using for the first time correct helicity density maps to determine the spatial distribution of magnetic helicity injection, we show the existence of a localized flux of positive helicity in the southern part of AR 10501. We conclude that positive helicity was ejected from this portion of the AR leading to the observed positive helicity MC.

Authors: R. Chandra, E. Pariat, B. Schmieder, C.H. Mandrini, W. Uddin
Projects: SoHO-MDI

Publication Status: accepted in Solar Physics
Last Modified: 2009-10-07 07:18
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Velocity vectors of a quiescent prominence observed by Hinode/SOT and the MSDP (Meudon)
How can a Negative Magnetic Helicity Active Region Generate a Positive Helicity Magnetic Cloud ?

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