INCOHERENT SCATTER RADAR OBSERVATIONS OF NON-MAXWELLIAN ION VELOCITY DISTRIBUTIONS IN THE

Observations by the EISCAT experiments “POLAR ” and Common Programme CP-3 reveal non-Maxwellian ion velocity distributions in the auroral F—region ionosphere. Analysis of data from three periods is presented. During the first period, convection velocities are large k2 km S ~) and constant over part of a CP-3 latitude scan; the second period is one of POLAR data containing a short—lived (<1 mm,) burst of rapid (>1.5 km ~_1) flow. We concentrate on these two periods as they allow the study of a great many features of the ion-neutral interactions which drive the plasma non—thermal and provide the best available experimental test for models of the 3— dimensional ion velocity distribution function. The third period is included to illustrate the fact that non—thermal plasma frequently exists in the auroral ionosphere: the data, also from the POLAR experiment, cover a three—hour period of typical auroral zone flow and analysis reveals that the ion distribution varies from Maxwellian to the threshold of a toroidal form. I NTRODUCTION The existence of non—thermal plasma in the auroral F—region was predicted theoreticaly by It— Maurice and Schunk, in a remarkable series of papers culminating in their 1979 review pape