Azimuthal distribution of HF slantEechoes and its relationship to the polar cap electric field

Abstract

A study was conducted to investigate the azimuthal distribution of high-frequency slant E echoes and its relationship to the polar cap electric field. Analysis of data obtained with a oblique step sounder and a rotatable log periodic antenna located at Resolute Bay, Canada, showed that the highest frequency of the slant E echo trace during any given azimuth scan was found to maximize in the direction of the E region current vector. This relationship is inferred from the striking 15-deg/h diurnal variation in the direction of the highest-frequency slant E echo, the change of this direction with the sign of the azimuthal component of the interplanetary magnetic field, and the general agreement of the direction of slant E echo maxima with the directions shown by equivalent current systems derived from polar cap magnetometer data. This directional relationships is interpreted in terms of conditions established by the Buneman-Farley two-stream instability, the magnetic aspect sensitivity, and the ionospheric refraction. Slant E echoes, which were also observed at angles near perpendicular to the current flow, are thought to be due to secondary plasma waves generated by a mechanism similar to that proposed by Sudan et al. (1973). The possibility that some of themore » slant E echoes used in the analysis are really slant F echoes remains to be investigated. (AIP)« less