Panel a: dependence of η⁽²⁾ on θ for the two regimes of low and high radio frequencies. The divergences will be smoothed by collisions and finite temperatures (our cold plasma treatment becomes invalid when the thermal speed of the particles exceed the phase speed c∕η⁽²⁾ of thewaves, so corrections will always set in at some stage for a diverging η⁽²⁾) (Motz 1966). Panel b: dependence of ζ in the polarization vector (15) on x, plotted with as given by Table 1. The locations of ω = 2π × 5 GHz and 2π × 0.5 GHz are marked out with vertical dashed lines.