On the collisional theory of the anisotropic solar wind plasma

The collisional equations for the solar wind assuming steady, spherically symmetric flow and including thermal conduction and an anisotropic proton temperature are analysed in the absence of a heat source function. The equations are cast in a form that involves one dimensionless parameter, effectively equal to the inverse Péclet number for protons, and the small quantity , the square-root of the electron-proton mass ratio. Analytic forms for the proton temperature anisotropy and other flow variables are derived by applying the limit 0, and using asymptotic techniques. It is found that the model based purely on Coulomb collisions predicts values for the proton temperature anisotropy in the vicinity of the Earth that are much smaller than those observed, and that increasing the coronal base temperature serves to decrease the predicted anisotropy still further.The National Center for Atmospheric Research is sponsored by the National Science Foundation.