Differential Delay of Ordinary and Extraordinary Modes of Transionospheric Radio Waves

The terrestrial ionosphere is a birefringent medium that allows radio waves to propagate in two modes: the ordinary (O-mode) and the extraordinary (X-mode). A difference in the index of refraction of the two modes results in differential delay (mode delay) between the O- and X-modes of radio waves propagating through the ionosphere. Mode delays of transionospheric high frequency radio waves are determined using the Radio Receiver Instrument (RRI) onboard the Enhanced Polar Outflow Probe (e-POP) on the CASSIOPE/Swarm-E satellite. Experiments between RRI and the SuperDARN radar at Saskatoon, Canada show large variabilities in mode delays. The mode delays are nearly constant in some experiments but other experiments have large variations. The mode delay observations could not be explained by the distance between the e-POP satellite and the radar, the foF2 values along the satellite track, nor whether the satellite track was across or along a SuperDARN radar beam. A combination of RRI observations and ray-trace modeling are used to investigate the mode delay of transionospheric radio waves.