During storm times, O+ can dominate both the pressure and the density in the plasma sheet. Because of the contribution from ion outflow, the plasma sheet is already oxygen‐rich prior to substorm onset. At substorm onset the fraction of O+ contributing to the pressure and density increases. In the O+ dominated thin current sheet the O+ ions are observed to stream from dawn to dusk across the tail, as predicted for nonadiabatic ions by Speiser (1965). We calculate the current contribution from these ions and find that they carry about 5–10% of the cross‐tail current. During a nonstormtime substorm the general behavior of the O+ is the same. However, because there is less O+ present, the O+ never dominates over H+, and the contribution to the cross‐tail current is even less.
