Depolarization of VHF geostationary satellite signals near the equatorial anomaly crests

Diffractive wave scattering by small scale density irregularities with power law spectra is proposed to be the process causing the intense and fast fluctuations of the SIRIO 136-MHz signals received at Ascension Island near the southern crest of the equatorial anomaly. The variances of phase shift, field amplitude ratio, Faraday rotation fluctuations, and the induced field component of transionospheric signals are formulated and evaluated for density irregularities of both power law and Gaussian types. The absence of the phenomenon at equatorial locations of the anomaly crests is attributed to the fact that the ambient plasma densities are relatively low, and the propagation angles of satellite signals are more nearly perpendicular to the geomagnetic field.