The charged‐particle fluxes at auroral and polar latitudes and related low‐frequency auroral kilometric radiation‐type and high‐frequency wideband emission

Abstract

The results of simultaneous observations of charged particle fluxes within the energy range 50 eV to 20 keV (plasma energy‐angle spectrometer, PEAS experiment) and plasma waves within the frequency range 0.1 to 10 MHz (plasma radio spectrometer, PRS 3 experiment) on board the APEX spacecraft are presented. The data were obtained at polar and auroral latitudes in the dawn‐dusk and noon‐midnight time sectors. The low‐frequency (LF) sporadic emission mainly on frequencies lower than the local gyrofrequency was commonly observed within a comparatively narrow latitude interval (∼5°– 6°) of the auroral oval. The maximum of spectral wave intensity was revealed at a frequency of ∼ 200 kHz. The sporadic character of the observed emissions, the spectra, are very similar to those reported for auroral kilometric radiation (AKR), and the temporal and spatial occurrences imply its relation to the source of AKR emissions measured at the higher altitudes, with regards to our wave measurements as LF AKR‐type emissions. Comparative analysis of spatial distributions of charged particle energy spectra and variations of wave spectra at auroral oval latitudes showed that several conditions should be fulfilled for LF AKR generation. These conditions are related both to the intensity and energy of precipitating ion and electron fluxes, and to albedo electrons and the ionospheric plasma parameters. The wideband HF emission was observed together with the LF AKR‐type emission during the morning auroral oval crossing. At spacecraft apogee altitudes, in the polar cap zone intense electron precipitations and an increase of plasma noise intensity at frequencies equal or below ƒHe were observed at the period when the IMF was northward These precipitations and emissions were accompanied by the horizontal currents crossing the polar cap, the so‐called theta structure.