Velocity of SuperDARN echoes at intermediate radar ranges

The study investigates the relationship between Super Dual Auroral Radar Network (SuperDARN) high-frequency (HF) radar velocities measured at intermediate ranges of 600–1,000 km from the radar and the E × B plasma drift. Two approaches are implemented. First, a 3-h interval of SuperDARN Rankin Inlet (RKN) radar measurements and Resolute Bay incoherent scatter radar RISR-C measurements in nearly coinciding directions is investigated to show that (1) HF echoes with low velocities (less than 200 m/s) are often detected when E × B drifts are in excess of 1,000 m/s; (2) high-velocity HF echoes from the E region have velocities somewhat below the expected values of the ion-acoustic speed of the plasma and the HF line-of-sight velocity does not show a tendency for an increase at the largest E × B drifts; (3) for E region echoes, 12 MHz velocities are slightly larger than those at 10 MHz; and (4) 12-MHz echoes are often received from the electrojet heights while 10-MHz echoes are received from the F region heights so that the observed velocities are quite different with the latter reflecting the E × B drift of the plasma. In the second approach, velocities of 10- and 12-MHz RKN echoes are compared for a large data set comprising several months of observations to show that occurrence of 12-MHz low-velocity echoes is fairly common (up to 25% of the time) whenever the plasma drifts are fast. Under this condition, the SuperDARN cross polar cap potential is underestimated, on average, by ∼4 kV.