Measurements of E region ionization and conductivity produced by solar illumination at high latitudes

Abstract

Electron density measurements made by the Chatanika radar during times when auroral particle precipitation was absent have been used to determine the variation of E region ionization and height‐integrated ionospheric conductivity as a function of solar zenith angle and solar flux. From the Chatanika radar data taken over an entire solar cycle we have derived the electron density as a function of altitude between 90 and 250 km for five solar zenith angles between 45° and 85° and for four different levels of solar flux. From 16 to 40 profiles were averaged together to determine the mean values; typically, the standard deviations were less than 25% of the mean. The height‐integrated conductivities computed from these profiles increase by about a factor of 2 between the lowest and highest levels of solar flux. The solar contribution to the Hall and Pedersen conductances ΣH and Σp is well represented by ΣH = 1.5 (Sa cox χ)0.5 = 1.7 Σp, where χ is the solar zenith angle and Sa is the 10.7‐cm solar flux. In order to determine the total conductance when other ionization sources are present the altitude‐dependent production rate is required. This was computed from the data by using an altitude‐dependent model for the effective recombination coefficient.