The Angular Momentum of the Solar Wind

A steady-state model of the solar-wind flow in the equatorial plane including the effects of pressure gradients, gravitation, and magnetic forces is developed and solved for both the radial and azimuthal motions. The viscosity is taken to be zero, the electrical conductivity to be infinite, and the energy supply characterized by a polytropic index. The solution must pass through three critical points, whose significance is explained in terms of the characteristic velocities with which disturbances propagate. A numerical solution is obtained for typical parameters The magnetic field produces only a modest tendency toward co-rotation of the outer corona, but the magnetic stresses apply a torque to the Sun equal to that required to produce effective co-rotation out to the radial distance where the radial Mach number equals unity. For typical solar-wind values this will occur between 15 and 50 solar radii out, which implies a substantial loss in the angular momentum of the Sun.