Partial reflections from equatorialEregion gradients

Anomalous narrow peaks in both daytime and nighttime equatorial E region VHF radar spectra observed when the electron drift is low appear to be explainable in terms of partial reflections from regions of sharp plasma density gradients. Both zero-order gradients and secondary gradients from steepened gradient drift irregularities may contribute to partial reflection enhancements of 10–20 dB over incoherent returns. Some of the anomalous peaks have Doppler shifts which appear to be consistent with the ambient ion-neutral drifts and independent of the electrojet (electron drift) direction. This may be due to the fact that both the steep zero-order gradients and the large irregularities that produce the partial reflections tend to predominate at somewhat lower heights, where the plasma is strongly collision dominated.