Figure 1. Plasma flow geometry in the vicinity of a nonmagnetic planet.
ionopause boundary of roughly 40 V. This corresponds to less than 0.1 percent of the solar-wind plasma incident on the planet penetrating the ionopause. The volume current distribution together with the conductivity allows determination of electric and magnetic fields everywhere within the ionosphere, and hence specifies the convection pattern of ionization within the ionosphere. A quantitative understanding of the distribution of ionization must clearly include these convective effects with diffusive and photochemical mechanisms.