A magnetohydrodynamic description of coronal helmet streamers containing a cavity

A three-dimensional axisymmetric time-dependent magnetohydrodynamic model has been used to obtain quasi-static helmet-streamer solutions that contain a cavity flux rope in their closed held region. The dynamical equilibrium of the cavity flux rope inside the closed region of the streamer can be described as the partial balance between the outward acting magnetic force and the pressure and gravity forces inside the flux rope, which, in addition, is held down by the helmet dome above. Our solutions indicate that the helmet streamer containing a cavity flux rope has more magnetic energy than the corresponding open field configuration, which means that the state transition from the former to the latter is permitted energetically. These solutions may serve as pre-event coronae for studying the initiation of coronal mass ejections.