Studies Of Fine Structures Of Prominences With Spectroscopic Data Taken By IRIS

Prominence is an important feature of the solar atmosphere observed above the solar limb,which is also called "filament" when observed on the solar disk.Its formation and evolution has been an important subject in the study of solar physics.The topological shape of the prominence is varied,which is closely related to the magnetic field and its formation mechanism.The prominence is usually composed of fine thread-like plasma structures.These thread-like structures embody the magnetic field shape of the prominence,so it is an important way for us to know the shape of the magnet field.IRIS(Interface Region Imaging Spectrograph)has high spatial and temporal resolution in both imaging and spectral observations.This provides us an excellent way to study the fine structure of prominences.In this study,we mainly use the imaging and spectral data of IRIS satellite to study the geometrical and dynamic information of threads,vertical flows and other small-scale plasma structures in prominences.We investigate two quiescent prominences and one intermediate prominence.In combination with imaging and spectral data,we identify several threads.We find that the width of threads is between 0.5 and 1 at the IRIS data resolution,which is consistent with the previous observations using Ha and SOT Ca II data.They are quasi-perpendicular to the solar surface when observed in the plane-of-sky,which were defined as vertical threads in previous studies.Through analyzing the imaging and spectral data,we find the plane-of-sky speed of vertical threads is between lOkm/s and 45km/s,and the Doppler velocity is between 10km/s and 49km/s.In combination with Doppler and plane-of-sky velocities,we infer an angle between threads and solar surface in the line-of-sight direction.We find all of the vertical threads which we studied are not vertical actually.Angles are mainly distributed in between 30 to 60 degrees.These threads more inclined to the solar surface.By investigating the angle of different locations of threads,we find the threads are not actually straight.They show some kinds like the wavy structure.We think this topological shape of magnetic field could provide magnetic tension for supporting plasma in prominences.Moreover,the result indicates that the different appearance of vertical and horizontal threads may be caused by the observing angle with respect to the prominence.On the other hand,we also confirm the counter-streaming flows at a same prominence by spectroscopic diagnosis and imaging tracking.This proves the complexity of plasma in prominences.We find that there may be two ways of mass losses of a prominence.One is the plasma along magnetic line to fall back to solar surface.The other is the plasma as small-scale blocks to fall off the prominence.In the evolution process of one prominence,we observed upward flows from one side and downward flows at the other side.Meanwhile,the bubble displays upward movement.The whole evolution process are more like Magneto-Thermal Convection model.Through investigating of these fine structures of prominence,we have a better understanding of the geometric structure,the magnetic field shape and the magnetohydrodynamics characteristics of the prominence.That will provide an important clue for researching the mechanism of the evolution of prominences by using multi-wavelength imaging and spectral data in the future.