ON THE SPECTRAL ASYMMETRY OF TYPE-II COHERENT ECHOES AT LARGE MAGNETIC ASPECT ANGLES

The asymmetry (skewness) of broad type II Doppler spectra collected by the pre Saskatchewan Auroral Polarimetric Phased Array Ionospheric Ra dar Experiment (SAPPHIRE) coherent radar System during westward electr ojet conditions was studied. The system included two 50-MHz CW links w hich monitored spatially close regions of the ionosphere with about th e same aspect angles of similar to 10 degrees but with an azimuth diff erence of the bisectors of about 90 degrees. Periods of scatter were s elected when both radar links recorded echoes with a wide, type II spe ctrum. 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 td be positive (negative) contrary to previous reported auroral zone expe riments (positive skewness means a longer spectral tail toward higher velocities). The spectra were more skewed for observations along the e lectrojet, 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.