Beaming of intense AKR seen from the Interball‐2 spacecraft

Abstract

We present results of intense auroral kilometric radiation (AKR) sources direction finding based on single‐spacecraft truek→ vector source location performed in the frame of Interball‐2 mission (POLRAD experiment on board Auroral Probe). With our swept frequency analyzer we are not able to work with single AKR bursts generated in small, elementary sources, but we improve our signal‐to‐noise (s/n) ratio and determine direction to the AKR source region averaging data over 10 consecutive 4 kHz frequency steps. Measurements of directions to the AKR sources confirm recent Mutel et al. () findings based on Cluster Very Long Baseline Interferometry (VLBI) data—AKR rays are mostly confined to the direction tangent to the auroral oval as measured in Mutel's tangent plane (TP) coordinates. In this paper we use additional coordinate system rotated with respect to TP coordinates in order to determine azimuths of AKR rays with respect to the auroral oval. We see cases of AKR propagation significantly deflected from the tangent plane. Additional information concerning geometry of auroral arc at the AKR source can help to distinguish between propagation along and propagation across the auroral cavity. Examples of instantaneous AKR visibility maps defined in this paper for both coordinate systems are shown and discussed. Using such map (valid for our spacecraft for relatively short observational periods of the order of 10 min), it is possible for known positions of the AKR sources in invariant latitude‐magnetic local time coordinates to visualize direction angles of AKR beams reaching the observer.

Global Occurrences of Auroral Kilometric Radiation Related to Suprathermal Electrons in Radiation Belts

“…The highest occurrences also occur in the nightside region within L = 6.0–6.5 for different AE index levels, with the most samples (198) in the bin L = 6.0–6.5 and 21–22 MLT during the period AE ≥ 300 nT. The occurrence of AKR exhibits a noticeable preference (1,740 samples in total) in the MLT = 20–24 and 00–02 sector within L = 5.5–6.5 when strong substorms occur (Figure e), which is the AKR source position in the MLT region based on the recent modeling (Schreiber et al, ). The lower panels in Figure show that the value of R ef is sensitively dependent on AE index, likewise.…”

“…AKR emissions have been systematically investigated since the first observation by ELECTRON-2 satellite in 1965 (Burinskaya, 2013;Liou et al, 2000;Mutel et al, 2006;Schreiber et al, 2017). Now it has been widely accepted that the fundamental process of AKR generation is the electron cyclotron maser instability (Pritchett et al, 2002;Wu & Lee, 1979).…”

Dominant Roles of High Harmonics on Interactions Between AKR and Radiation Belt Relativistic Electrons

“…The original regions of AKR mode waves are low‐density auroral source zones above altitudes 1–3 R E (Earth radii) along magnetic field lines (Gurnett, 1974; Huff et al., 1988; Kurth, Baumback, & Gurnett, 1975). It is widely accepted that AKR emissions are generated by cyclotron maser mechanism with the dominant occurrence staying in the right‐hand extraordinary (R‐X) mode (Burinskaya, 2013; Melrose, 1986; Pritchett, 1984), which is strongly supported by numerous observations (Calvert, 1981; Liou et al., 2000; Pritchett et al., 2002; Schreiber et al., 2017). Summers et al.…”

Is the AKR Cyclotron Maser Instability a self-organized criticality system?

“…The SOC concept can be applied to the Cyclotron Maser Instability (CMI) responsible for the AKR generation as well. We observe the AKR radiating region consisting of a bunch of small elementary AKR sources which are located within the auroral oval [Mutel et al, 2008;Schreiber et al, 2017]. After reaching the threshold of CMI instability in the source region, we observe many elementary AKR sources "firing" with different intensities -that corresponds to the avalanche in the SOC definition.…”