Comparison of the viscous isothermal solutions to the analytical (inviscid) Parker solution. The black curves represent contours of De Leval’s Equation (32). Of these, only the black dashed-dotted curve(s) exhibits a sonic point at the allowed critical point, consistent with Parker’s description of a transonic solar wind. The variously colored blue, yellow, and red curves are numerical solutions to the viscous isothermal equations. The dashed blue curve is a subsonic breeze solution for which to u → 0 as s → ∞. The dashed yellow (divergent wind) and red (shocked breeze) curves are transonic solutions that exhibit either u → ∞ or u → 0, respectively, as s → ∞. The constraint matching solution (solid teal curve) satisfies the boundary condition σ(s = 1 AU) = 0.