AN MHD MODEL FOR SOLAR CORONAL PLUMES

Solar coronal plumes are modelled by solving the steady, ideal, 2-D, m agnetohydrodynamic (MHD) equations and assuming azimuthal symmetry aro und the plume axis. Since magnetic fields are believed to play an esse ntial role in plume formation and structure, a self-consistent method of linearisation of the MHD equations with respect to the magnetic fie ld has been considered here. This consists of three distinct steps: fi rst a potential field is calculated as a deviation from the radial cas e due to a flux concentration at the plume base, then the other plasma quantities are worked out by solving a Bernoulli-like equation and fi nally the modifications to the zeroth order field are found. Free func tions 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 repro duce basic features of coronal plumes such as the super-radial expansi on close to their base. The results are compared with the observations .