On the spectral asymmetry of type II coherent echoes at large magnetic aspect angles

Abstract

The asymmetry (skewness) of broad type II Doppler spectra collected by the pre Saskatchewan Auroral Polarimetric Phased Array Ionospheric Radar Experiment (SAPPHIRE) coherent radar system during westward electrojet conditions was studied. The system included two 50‐MHz CW links which monitored spatially close regions of the ionosphere with about the same aspect angles of ∼10° but with an azimuth difference of the bisectors of about 90°. Periods of scatter were selected when both radar links recorded echoes with a wide, type II spectrum. Typically, the spectra were asymmetrical on both links and had a magnitude of skewness in between 0.3 and 0.5. For radar links with a positive (negative) mean Doppler shift, the skewness was observed to be positive (negative) contrary to previous reported auroral zone experiments (positive skewness means a longer spectral tail toward higher velocities). The spectra were more skewed for observations along the electrojet, for higher echo power and also for narrower spectral width. The characteristic features of the spectral asymmetry are attributed to the plasma turbulent processes at large off‐orthogonal angles.