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

Abstract

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 ø-6 ø) 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 shotfid be fidfilled 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 fm 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 them structure.

Further evidence for a connection between auroral kilometric radiation and ground‐level signals measured in Antarctica

“…Subsequently, further evidence of low‐altitude AKR‐like signals has emerged from observations with low‐Earth‐orbiting satellites [ Shutte et al , ] and sounding rockets [ LaBelle et al , ]. The latter paper also showed an example observed at ground level in northern Canada.…”

DEMETER observations of bursty MF emissions and their relation to ground‐level auroral MF burst

“…There have been comparisons between ground level MF burst measurements and particle data from low‐altitude satellites [ Sato et al , ; LaBelle et al , ]. However, there have been no simultaneous observations of MF bursts at ground level and by nearby spacecraft, even though there have been multiple observations of broadband MF emissions from low‐altitude satellites in the morning auroral oval [ Shutte et al , ] and in the topside cusp ionosphere [ Rothkaehl , ].…”

Ground-level detection of auroral kilometric radiation

“…Hence its discovery, which came twenty years after the discovery of Jovian decametric radiation, relied on suitably instrumented spacecraft a large distance (>5000 km) from Earth. Nevertheless, over the years there have been occasional reports of AKR‐like emissions observed at low altitudes from rocket‐borne, low‐earth‐orbiting satellite borne, and ground based receivers [e.g., Oya et al , 1985; Morioka et al , 1988; Beghin et al , 1989; Shutte et al , 1997; LaBelle et al , 1999]. In particular, Oya et al [1985] championed the idea of “leaked AKR” as an explanation for AKR‐like signals observed with the low‐Earth‐orbiting EXOS‐C satellite.…”