MAGNETIC-STRUCTURE OF SOLAR PROMINENCES

The cold and dense prominence plasma is suspended in the core of an arcade of magnetic field lines above the solar photosphere. The observations reveal a rather uniform horizontal component of the magnetic field of the order of 10(-3) T, predominantly directed close to the prominence long axis. On the other hand, monochromatic observations of the prominence fine structure provide a visualization of the magnetic configuration in the core of an arcade revealing intricate morphological structures and chaotic plasma flows. Prominences are usually modelled in cylindrical or slab geometry, assuming that the fine structure is only superposed on a larger scale magnetic field structure. MHD models often treat a prominence as a 2-D static feature but it seems that 3-D dynamical models, including real geometry, are necessary to comprehend the prominence phenomenon completely. The models predict a number of possible MHD instabilities which can cause a prominence eruption. When the critical conditions in an arcade are met (usually expressed as a critical shear or twist) the large scale magnetic structure erupts, together with the embedded prominence, and this eruption is known as a coronal mass ejection.