General dispersion relations for a hot magnetoplasma are used to explain the interference observed between electrostatic waves and the electromagnetic field in an afterglow plasma. Observations are made near both oblique resonance cones (connected with whistler and Z-propagation modes) and in the frequency region corresponding to “Bernstein” waves. Independent measurements of the lower (whistler) and upper (Z-mode) resonance cones, for a particular case, lead to the same isotropic temperature in the late afterglow, namely 540 K. Independent measurements of the lower resonance cone and of Bernstein waves in the early afterglow also lead to consistent isotropic temperatures. As the real and imaginary components of the wave number increase, a point of inflection is reached on the various dispersion curves for homogeneous plane waves beyond which these curves can no longer be used to explain the observed interference fringes. For homogeneous waves with a wave number smaller than that corresponding to the inflection point, reasonable values of Landau damping are obtained which agree roughly with observed damping.