The O+ and NO+ ion velocity distributions in the presence of a large electric field are analytically calculated for the auroral F region, taking into account the collisions with atomic and molecular neutral constituents. We have found an angle of 21¿¿1¿ with respect to the magnetic field direction where the O+ one-dimensional line-of-sight velocity distributions display a Maxwellian shape while the NO+ distribution function is nearly a Maxwellian. A scenario for the measurement of the auroral plasma parameters is discussed. The radar spectrum obtained for the specific angle of 21¿ depends on five parameters: electron density, electron temperature, ion composition, and two ion line-of-sight temperatures. With this reduced number of plasma parameters the fit from radar spectra is nevertheless ambiguous. To resolve this dilemma it is necessary to get an independent measurement of one of these five parameters. The plasma line observation is shown to provide a simultaneous measurement of the electron temperature. From simultaneous measurements of the ion line-of-sight temperatures, made at an angle away from 21¿ the thermodynamical temperature, as well as the ion temperature anisotropies, would be determined. ¿ American Geophysical Union 1993