THE MAGNETOHYDRODYNAMIC EQUILIBRIUM OF CORONAL HELMET STREAMERS

The equilibrium of coronal helmet streamers is investigated within the framework of an axisymmetric magnetohydrodynamic polytropic model. Th e main features of this work are: (i) The eight MHD vector equations a re reduced - via analytical manipulations - to three scalar equations involving the magnetic flux function, the current density and temperat ure; (ii) The reduced system of equations is solved by the aid of a co mputational algorithm including both relaxation and iterative techniqu es, and is continued until the maximum local relative change with time becomes smaller than 10(-4); (iii) At the Sun, only three physical qu antities are fixed, namely, the radial component of the magnetic field , the temperature and the particle density. The other quantities - the theta-magnetic field, radial and theta-components of the streaming ve locity - are determined in a self-consistent way; (iv) The coronal hel met streamer structure is obtained by: specifying the (observed) latit ude extension on the sun of the region of closed magnetic field lines, requiring the field lines in the meridian plane to become purely radi al at 10 solar radii, and imposing the continuity condition on the fie ld line separating the region of closed field lines from that of open field lines. The algorithm used in this work enables the separate anal ysis of the following problems of interest: (i) the linear problem - p lasma acceleration in a prescribed helmet streamer-like configuration; (ii) The quasi-linear problem - the feedback effect of the plasma (so lar wind) flow on the vacuum magnetic configuration; and (iii) the non -linear problem - the consistent equilibrium state of the magnetic fie ld and plasma flow in coronal helmet streamers. The quantitative resul ts obtained in these studies are presented, compared and discussed.