  The solar corona is a complex system, with nonisothermal plasma and being in
the self-gravitating field of the Sun. So the corona plasma is not only a
nonequilibrium system but also a nonextensive one. We estimate the parameter of
describing the degree of nonextensivity of the corona plasma and study the
generalization of the solar wind speed theory in the framework of nonextensive
statistical mechanics. It is found that, when use Chapman's corona model (1957)
as the radial distribution of the temperature in the corona, the nonextensivity
reduces the gas pressure outward and thus leads a significant deceleration
effect on the radial speed of the solar wind.
