Solar cycle and seasonal variations of the ionosphere observed with the Chatanika incoherent scatter radar


  • M. J. Baron,

  • C. J. Heinselman,

  • J. Petričeks


An incoherent-scatter radar facility was operated at Chatanika, Alaska (geographic and invariant latitudes both ≈ 65°N) for almost 11 years, essentially a full solar cycle. During this period, experiments lasting 24 hours and directed at nearly overhead measurements were made approximately once per month. The seasonal and solar cycle dependences of the ionosphere over Chatanika as deduced from 108 experiments spanning the 11 years are presented. The basic parameters measured were electron concentration, electron and ion temperatures, and line-of-sight ion velocity, all as functions of altitude and time. This paper focuses on the ionization in the E and F regions. Empirical relationships were found that enable (1) the daytime maximum E region electron concentrations to be expressed in terms of the 10.7-cm solar flux and the solar zenith angle, and (2) the daytime maximum F region electron concentration to be expressed in terms of the 10.7-cm solar flux alone. The dependence of nighttime precipitation-produced ionization in both E and F regions on solar flux and magnetic activity is also described. A clear distinction between summer and winter F region ionization conditions is evident, as is the rapid switchover near the equinox.