ELECTRON-TEMPERATURE AND DENSITY AT HIGH-LATITUDE

The background electron temperature and density at altitudes between 1 000 and 8000 km at invariant latitudes > 60 degrees have been determin ed from swept Langmuir probe measurements from the S3-3 satellite. The se plasma parameters are determined by fitting the measured probe curr ent-voltage relation to the expected theoretical response. Statistical ly acceptable fits are found for similar to 20% of all measurements an d do not include measurements within the auroral density cavity. The r esults indicate that the density varies as an inverse power law with i ncreasing altitude which has a typical value of 10 cm(-3) at 8000 km i n altitude. The electron temperature shows a slight increase with alti tude but is < 5 eV for almost all measurements. These results suggest that the background plasma outside of auroral density cavities on high -latitude field lines below 8000 km is dominated by cold plasma of ion ospheric origin which is at least an order of magnitude more dense tha n hotter magnetospheric components.