NO-REGION DURING ION FRICTIONAL HEATING EVENTS, FOUND IN EISCAT-CP1-DATA( ENHANCEMENT IN THE AURORAL F)

Experimental evidence is given for an increase of the molecular ion co ntent in the height range 180-300 km during several 'ion frictional he ating events': height profiles of the ion temperature, found in EISCAT -CP1-data, show minima of several 100 K between 210 and 260 km, as com pared to the lower and upper F-region. These minima are shown to te ma inly due to an enhancement of the NO+ concentration, which is interpre ted as a low ion temperature by the standard EISCAT fit. Following thi s assumption the O+ molecular ion ratio is calculated from the differe nce between measured and theoretical height profiles of the ion temper ature parallel to the magnetic field. Further the O+, NO+ and O2+ cont ent is calculated from the chemical reaction equations, considering th e temperature dependence of the reaction As a common result of the dif ference methods of calculation the NO+ content below 300 km increases considerably during the analysed ion heating events. At 200 km the Ocontent decreases from 50% by 5-20% and the transition zone from molec ular ion to O+ dominance can rise from 200 up to 260 km. In one event there is also indication for an increase of the molecular ion abundanc e by 20% at 300 km.