Beaming of intense AKR seen from the Interball-2 spacecraft

摘要

We present results of intense auroral kilometric radiation (AKR) sources direction finding based on single-spacecraft ?k 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. (2008) 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.