DAYTIME ION COMPOSITION IN HEIGHT RANGE OF 150-1500-KM FOR SOLAR MINIMUM CONDITION

An ion composition model for the height range 150-1500 km, likely to hold for day-time at moderate latitudes for minimum solar activity (F10.7 = 70 units† † 1 unit = 10-22 W/m2/cps of 10.7 cm solar radiation.) has been developed. It is based on the neutral atmospheric model given by Bhatnagar and Mitra (1966), solar ionizing flux data given by Hinteregger et al. (1965) and the electron and ion temperatures given by evans (1965) close to minimum solar activity period. The topside ionosphere has been considered as a ternary mixture of atomic oxygen, helium and atomic hydrogen ions. The calculated distribution of O+ agrees with that observed in the bottomside F2-region, if the rate coefficients k1 and k2 for the charge exchange between O+ and N2, and O+ and O2 have values of about (0.9-1.0) × 10-12 cm3/s and (0.9-1.0) × 10-11 cm3/s respectively, at F-region temperatures. These values agree within a factor of 2 with measured laboratory values. In the case of helium ions a reasonable agreement between the calculated and observed values is obtained, if the rate coefficients k3 and k4 for the charge exchange between He+ and N2, and He+ and O2 have values of about 10-11 cm3/sec. In the ease of atomic hydrogen ions, agreement between the calculated and observed values is obtained, if the neutral atomic hydrogen distribution from the atmospheric model is increased by a factor of about 5-10. It is concluded that the electron and ion temperatures in the topside ionosphere above about 500 km, obtained from incoherent scatter technique are larger than those required to explain the observed ionic composition at dip values around 60° for low solar activity conditions. © 1969.