A two-fluid model of the solar wind with appropriate boundary conditions is used to describe the average behavior of electrons and protons in the expanding solar corona. Rotation, viscosity, and magnetic fields are neglected. Ordinary "collisional" coupling between the two species gives particle density, bulk velocity, and electron temperature close to the observed average values at about 1 a.u. However, the proton temperature is too low, providing a temperature ratio at I a.u. of T /Tp 17 (instead of the observed value of about 4). Consideration of a "noncollisional" coupling about 30 times larger than the collisional one provides the proper proton temperature in addition to the other parameters. Thus, since no external nonthermal heating source beyond the "critical" distance is required, unstable wave-particle interactions are clearly indicated to be responsible for the obse;'ved fluidlike behavior of the solar wind. Increased coupling (artificially high) brings the two-fluid solutions, as required, close to those given by one-fluid equations.
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Cuperman et al. (1970) studied this question.