The effect of viscosity and anisotropy in the pressure on the azimuthal motion of the solar wind

A steady state axially symmetrical model for the flow of the solar wind near the equatorial plane is developed. The radial motion is regarded as known, and the azimuthal motion is investigated, allowing for magnetic forces, viscosity (as modified by the magnetic field), and anisotropic pressure. We show that to obtain a smooth continuous solution the constant of integration has to be determined, not from a boundary condition at the sun, but by the behavior of the solution near the critical radius rA, where the radial Mach number is unity. The viscosity considerably increases the tendency toward corotation in the region between five solar radii and 1 AU. The azimuthal velocity predicted near the earth is of the order of 6 km/sec for what may be regarded as typical conditions (temperature of 2× 05 °K and a radial wind velocity of 400 km/sec), whereas the velocity is 1 km/sec for a nonviscous isotropic model.