경희대학교 BK21

 

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● 날짜 : 2017년 09월 27일 (수요일)
● 시간 : 16시 30분
● 장소 : 천문대 영상실
● 강사 : Brigitte Schmieder (Paris Observatory)
 
Title : Magnetic field and plasma  conditions in  prominence/tornado B.Schmieder
 
Abstract :
Magnetic field configuration in prominences have been insensitively studied by  extrapolation of photosphere magnetic field and by numerical simulations. After a brief introduction on the models, I will define the main characteristics of what is called a tornado and  show many observations found in the literature and made by our group. s Several prominences were observed during campaigns in September 2013 and July 2014 with the IRIS spectrometer and the vector magnetograph THEMIS (Tenerife). SDO/AIA and IRIS provided images and spectra of prominences and tornadoes corresponding to different physical conditions of the transition region between the cool plasma and the corona. The vector magnetic field was derived from THEMIS observations by using the He D3 depolarisation due to the magnetic field. The inversion code (PCA) takes into account the Hanle and Zeeman effects and allows us to compute the strength and the inclination of the magnetic field which is shown to be mostly horizontal in prominences as well as in tornadoes. We used different observations to characterize the plasma. Movies from SDO/AIA in 171 A, Hinode/SOT in Ca II, IRIS spectra show the highly dynamic nature of the fine structures. From spectra in Mg II and slit  jaw images provided by IRIS we derived the Doppler shifts and the transverse velocity field of the fine structures and reconstructed the 3D structure of tornadoes.
 H-alpha observations  by the Multi-channel Subtractive Double Pass (MSDP) spectrograph in the Meudon Solar Tower provided maps of Dopplershifts in tornadoes.
We found that the Dopplershifts in Halpha  show some oscillation behaviour but not a systematic blue and red shift around the main axis as  it was suggested for tornadoes observed in coronal lines.  We will discuss on the different mechanisms which could lead to such observations.