Radar scatter from equatorial electrojet waves: An explanation for the constancy of the Type I Doppler shift with zenith angle

Abstract

The first results from the 430 MHz Advanced Modular Incoherent Scatter Radar Prototype (AMISR‐P) at the Jicamarca Radio Observatory were reported by Hysell et al. (2007). We present additional data showing that the phase velocity of Type I echoes is independent of zenith angle, an unexplained property of these waves. We interpret the results using rocket data by predicting the total line‐of‐sight velocity at the four zenith angles used. We find that the radars preferentially detect waves within 10% of Cs in at least four range gates for all beams and up to eight range gates for the 51 JULIA beam. This result is consistent with recent auroral observations that Type I waves are only generated with k vectors near the electron flow velocity, where the latter is the vector sum of the zero‐order drift and the perturbation drift due to large‐scale waves in the equatorial case.