Low-frequency fluctuations of the electric field in the equatorial ionosphere

Abstract

High time-resolution radar measurements of ionospheric electric fields have recently permitted studies of low-frequency hydromag-netic waves, but most of the research has depended on electron drift velocity from data obtained from the Scandinavian Twin Auroral Radar Experiment (STARE), taken at high latitudes (λ_m ∼ +70°) and used to study oscillations with periods of 200–300 s. At high latitudes, the low-frequency pulsations provide important information on the magnetospheric plasma process^1–3, but, at low latitudes, coupling of the ionosphere and magnetosphere remain unexplored. The purpose of our study is to examine the fluctuations in the electric field on a time scale longer than ion cyclotron periods, T_ci ∼ 0.6 s (ref. 4), or for frequencies ω ≪ ω_ci ∼ 10² rad s⁻¹ (the ion cyclotron frequency in the equatorial ionosphere), which haye not been studied at low latitudes. We report here observations of these waves with periods larger than 45 s from the high time-resolution data taken at Jicamarca, Peru.