Swarm-measured electron densities are smaller than those measured by incoherent scatter radars (ISR) radars at conjunctions by about 35% • The linear fit line to Swarm vs. ISR electron density plots has a slope of ∼0.62 • The effect of smaller Swarm electron densities is stronger at nighttime

The Empirical Canadian High Arctic Ionospheric Model (E-CHAIM) is an empirical climatological model of high latitude (above 50°N geomagnetic latitude) ionospheric electron density. The source code for E-CHAIM in the C, Matlab, and IDL languages is currently openly available online at https://e-chaim. chain-project.net. E-CHAIM was designed as an alternative to the use of the International Reference Ionosphere (IRI; Bilitza, 2018) at high latitudes, which was previously demonstrated to suffer significant limitations in that region (

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. Plain Language Summary This paper compares line-of-sight velocities measured by the SuperDARN radar at Rankin Inlet (RKN) with plasma flow measurements made by an incoherent scatter radar in about the same direction. The study focuses on RKN ranges where ionospheric echoes can arrive not only from the F region (~300 km) but also from the much lower E region (~100 km). We investigate one event when the flow was fairly uniform, roughly along the radar beams and fast with plasma drifts up to 1 km/s. We show that despite fast-flowing plasma, RKN occasionally detects low-velocity echoes not related to the plasma drift. Traditional E region echoes with velocities consistent with the ion-acoustic speed were also observed. However, for a number of ranges, the 12-MHz low-velocity echoes were received from E region heights while 10-MHz echoes, with the velocity close to the plasma drift, were received from F region heights. The velocity ratio in these cases was on the order of 3. We then show that such a situation may occur up to 25% of the time for the RKN radar. In these cases, SuperDARN cross polar cap potential can be underestimated up to 10 kV.

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