Ion Transients in the Polar Wind

The time evolution of field-aligned current-generated transient features in the high-latitude ionosphere is investigated. Ionospheric return currents generate signdicant downward heavy ion flows in the topside ionosphere with peak values well exceeding 10 scm'2s 'i. When the return current ceases the polar ionosphere rapidly returns to its previous equilibrium state. During the recovery phase of the return current event an upward propagating heavy ion transient is formed, which is mainly characterized by a relatively short O '• upwelling event. On the other hand, the H + escape flux remains relatively constant (within 10-20%) during field-aligned current events. It is also found that upward currents generate a transient heavy ion outflow, which exceeds the ambient H+ escape flux by a factor of 3 to 5, depending on the duration and strength of the field-aligned current event.