  Some basic structures in planetary nebulae are modeled as self-organized
magnetohydrodynamic (MHD) plasma configurations with radial flow. These
configurations are described by time self-similar dynamics, where space and
time dependences of each physical variable are in separable form. Axisymmetric
toroidal MHD plasma configuration is solved under the gravitational field of a
central star of mass $M$. With an azimuthal magnetic field, this self-similar
MHD model provides an equatorial structure in the form of an axisymmetric torus
with nested and closed toroidal magnetic field lines. In the absence of an
azimuthal magnetic field, this formulation models the basic features of bipolar
planetary nebulae. The evolution function, which accounts for the time
evolution of the system, has a bounded and an unbounded evolution track
governed respectively by a negative and positive energy density constant $H$.
