Eiscat observations of strong ion outflows from the F-region ionosphere during auroral activity: Preliminary results

Observations of large outward field-aligned flows of the bulk ion population in the F region during auroral activity are presented. These ion outflows are most commonly observed within auroral arcs, and are not well correlated with diffuse aurora. The ions (mainly O+) may reach field-aligned outward velocities of more than 500 m/s and the calculated ion fluxes usually reach 1013 m-2 s-1. Strong electron temperature enhancements in the F region are observed in connection with almost all ion outflow events. However, high electron temperatures are not always an indicator for these strong ion outflow events. Our measurements have been carried out at the EISCAT incoherent scatter facility near Tromso, Norway. The exact mechanism causing the ion outflow is not yet understood, but several possible mechanisms are briefly discussed. copyright American Geophysical Union 1989