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 (λm ∼ +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 process1–3, 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, Tci ∼ 0.6 s (ref. 4), or for frequencies ω ≪ ωci ∼ 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.