ELECTRON HEAT-FLOW IN THE AURORAL IONOSPHERE INFERRED FROM EISCAT-VHFOBSERVATIONS

At auroral latitudes the electron heat flow resulting from solar EUV h eating, as well as magnetospheric energy input, are important paramete rs which drive the thermal electron structure of the upper ionosphere. A method is presented which allows a determination from EISCAT-VHF ob servations of the heat flow at two altitudes, typical of the collision -dominated F2 region and of the topside ionosphere. EISCAT midwinter a nd near-summer observations are used to illustrate the method: diurnal and seasonal variations of solar origin are evidenced, with peculiar enhancements at sunrise and sunset that are interpreted as a delay bet ween the F2 level and topside terminator passage. Perturbations of mag netospheric origin are then discussed. One of them is characteristic o f low-altitude energy inputs. Others correspond to high-altitude energ y inputs through heat flow variations and are interpreted as upward cu rrents of the order of 14 muA m-2.