Excitation and absorption of ULF oscillations studied by high-latitude Doppler radar data

Abstract

Maps for standard deviations of the drift velocity of E layer ionosphere electrons in the radar field of vision were constructed with the aid of narrowband and low-pass filtering based on STARE Doppler data. In these maps, narrowband filtering reveals the geometric configurations of the excitation of particular ultralow-frequency (ULF) oscillations. Such a configuration indicates nonresonant origins of these oscillations. Low-pass filtering of the Doppler data revealed specific absorption of background ULF signals; this absorption is attributed to the resonance of magnetic field lines. Quantitative estimates for minimum frequencies of the resonant ULF absorption occurring in the eigenfrequency continuum of magnetic field lines were found.