Origin and dynamics of multi-component (H+/He++/He+/O+) ion flows in the lobe/mantle regions Original Research Article

Over a wide range of tailward distances in the lobe/mantle regions of the Earthʹs magnetotail (<210 RE), the Geotail spacecraft sometimes observed multi-component ion flows (MCIF) consisting of both ionospheric (H+/He+/O+) and solar wind (H+He++) ions. All ion species in the MCIFs are streaming tailward with nearly the same velocity to each other. A positive correlation between proton density and the flow velocity ∥v∥ suggests that most of protons have come from the solar wind. The existence of He++ further supports this suggestion. The lack of positive correlation between O+ as well as He+ density and ∥v∥ is consistent with the idea that these ions have a different origin from protons, i.e., the ionosphere. Another remarkable feature is that the He+ and O+ beams often appear to exist nearly exclusively of each other on a short time scale, and even when He+ and O+ coexist, their densities are sometimes anti-correlated. When the ionospheric ions have undergone an energization which leads to a different velocity for different ion species, the observed alternating appearance and anti-correlation are explicable only if a velocity filter is applied after the energization. A mechanism leading to similar velocities, on the other hand, needs an alternating enhancement of He+ and O+ fluxes in a source region to explain an anti-correlation.