EISCAT OBSERVATIONS OF TOPSIDE IONOSPHERIC ION OUTFLOWS DURING AURORAL ACTIVITY - REVISITED

New EISCAT observations of large field-aligned bulk ion outflows from the topside ionosphere during auroral activity are presented. The ions (mainly O+) start their outflows from a variable altitude and may reach field-aligned outward velocities of up to 1500 m s-1 in the altitude region 900-1500 km. The observed ion fluxes are about a factor of 10 larger than previously observed reaching 2 x 10(14) m-2 s-1, and in some cases is nonconstant with altitude. Two different types of ion outflows have been identified. The first type is related to periods of strong perpendicular electric fields, enhanced and anisotropic ion temperatures, and low electron densities below 300 km, indicating small amounts of auroral precipitation. The second type is related to auroral arcs and enhanced electron temperatures. The exact mechanism causing the ion outflows is still not yet understood, but additional mechanisms other than thermal expansion are required to explain the observations presented here.