An MHD model for solar coronal plumes.

Solar coronal plumes are modelled by solving the steady, ideal, 2-D, magnetohydrodynamic (MHD) equations and assuming azimuthal symmetry around the plume axis. Since magnetic fields are believed to play an essential role in plume formation and structure, a self-consistent method of linearisation of the MHD equations with respect to the magnetic field has been considered here. This consists of three distinct steps: first a potential field is calculated as a deviation from the radial case due to a flux concentration at the plume base, then the other plasma quantities are worked out by solving a Bernoulli-like equation and finally the modifications to the zeroth order field are found. Free functions of the model are the radial field component at the coronal base, the density at the coronal base and the temperature, which is assumed to be constant along the field lines. This method allows one to reproduce basic features of coronal plumes such as the super-radial expansion close to their base. The results are compared with the observations.