A satellite with a radio sounder is an excellent measuring tool for studying the structure and dynamic behavior of the plasmasphere and its abrupt outer boundary, the plasmapause.

The theory of ion collection at the center of a moving electrically charged blunt-electrode (probe) in the ionospheric D region is considered at high velocities such that the boundary layer is thin. The stagnation-point boundary-layer analysis of Sonin (1967) is reviewed where diffusion, mobility, and convection are coupled within the thin boundary layer at infinity Debye length. A critical parameter is the ion Péclet number P, which is essentially...