Polar-cap patches as a source of Doppler spread in the polar-cap: a case study

• Doppler curve for ePOP-RRI-CLY conjunction shows dramatic variability in ~500 Hz, especially during 100-250 s elapsed. • Received signal power also shows an eastward shift in the expected position of CLY's peak power. • Consistent with QAN-ALE deviations in Fig. 2. • e-POP RRI's motion across CLY's field-of-view, , generates a Doppler shift, (Ponomarenko et al., 2009): where , is radar wavelength, is plasma density, and is a differential path length between positions (CLY) and (e-POP RRI). • Hypothesis: variability due to polar-cap patches, represented by the first term.