Electron temperature and ion composition in theF₁region

By employing a radar system operating at 23-cm wavelength with the beam directed obliquely, it has been possible to obtain Thomson scatter echoes from the ionosphere in the height range 100–300 km that are free from ‘ground clutter’ contamination. The measurements obtained with this system therefore supplement earlier results obtained using the Millstone Hill ionospheric radar, which has a vertically directed beam, and make it possible to obtain the electron and ion temperature distribution over the entire height interval 130–800 km approximately. The interpretation of the signal spectrums obtained with the oblique incidence radar requires that an assumption be made about the temperature of either the electrons or the ions, or about the ion composition. In the analysis presented here of the 1964 measurements it was assumed that the ion and neutral temperatures are the same up to a height of about 250 km and that only O+ ions prevail at this height. Thus the ion temperature could be determined for 250-km altitude, and its dependence for lower heights was assumed to follow the same exponential law as in the CIRA 1965 model atmosphere. It was then possible to determine the electron temperature and the ratio of (O+) to (O2+ + NO+) ions in the height range 135–250 km. These results are presented and compared with rocket determinations.