Observations by six Super Dual Auroral Radar Network (SuperDARN) polar cap radars, three in the northern hemisphere and three in the southern hemispheres, are considered to assess F region echo occurrence rates over solar, season, and day cycles and to establish relationship between the echo occurrence rate and the background electron density and plasma flow velocity magnitude. The echo occurrence rate is shown to increase toward the solar cycle maximum, more distinctly on the nightside, consistent with a general trend of the background electron density. Over the last 5 years, the echo occurrence rates decline at a rate of 5-10% per year. The pattern of seasonal and diurnal variations in echo occurrence is found to be consistent with previous SuperDARN publications. Minor dips in echo occurrence rate are observed in winter solstices, and these are related to an overall decrease in the electron density. In most of the time sectors, the echo occurrence rate increases with the electron density but only up to a certain threshold value after which the dependence saturates. The level of the saturation depends on season, local time, and average plasma flow velocity magnitude. For the summer daytime observations, the echo occurrence rate correlates with variations of both electron density and plasma flow velocity magnitude.

Measurements of the electron density at the F region peak by the Canadian Advanced Digital Ionosonde (CADI) and the Resolute Incoherent Scatter Radar (RISR) are used to assess the quality of peak electron density estimates made from elevation angle measurements by the Super Dual Auroral Radar Network (SuperDARN) high-frequency radar at Rankin Inlet (RKN). All three instruments monitor the ionosphere near Resolute Bay. The CADI-RKN joint dataset comprises measurements between 2008 and 2017 while RISR-RKN dataset covers about 60 daylong events in 2016. Reasonable agreement between the RKN estimates and measurements by CADI and RISR is shown. Two minor discrepancies are discussed: RKN radar daytime peak electron density overestimation by ~ 10% and underestimation by up to 30% in other time sectors. In winter nighttime and dawn, cases were identified in which the RKN radar significantly overestimates the peak electron density. This occurs when the phase in the RKN interferometer measurements is incorrectly shifted by 2π , and this is most significant when electron densities are low. Statistical fitting to the joint data sets, split into four time sectors of a day, has been done and parameters of the fit have been determined. These allow slight adjustment of measured real-time RKN values to better reflect real peak electron densities in the ionosphere within its field of view.

Ground scatter (GS) echoes in Super Dual Auroral Radar Network (SuperDARN) observations have been always expected to occur under high‐enough electron density in the ionosphere providing sufficient bending of high frequency radio wave paths toward the ground. In this study, we provide direct evidence statistically supporting this notion by comparing the GS occurrence rate for the Rankin Inlet SuperDARN radar and the F region peak electron density NmF2 ${N}_{m}{F}_{2}$ measured at Resolute Bay by the Canadian Advanced Digital Ionosonde and incoherent scatter radars RISR‐N/C. We show that the occurrence rate increases with NmF2 ${N}_{m}{F}_{2}$ roughly linearly up to about ∼4⋅1011m−3 $\sim 4\cdot {10}^{11}{\mathrm{m}}^{-3}$ and the trend saturates at larger NmF2 ${N}_{m}{F}_{2}$. One expected consequence of this relationship is correlation in seasonal and solar cycle variations of the GS echo occurrence rate and NmF2 ${N}_{m}{F}_{2}$. GS occurrence rates for a number of SuperDARN radars at middle latitudes, in the auroral zone and in the polar cap are considered separately for daytime and nighttime. The data indicate that the daytime occurrence rates are maximized in winter and nighttime occurrence rates are maximized in summer for middle latitude and auroral zone radars in the Northern Hemisphere, consistent with the winter anomaly (WA) phenomenon. The effect is most evident in the North American and Japanese sectors, and the quality of WA signatures deteriorates in the European and, especially, in the Australian sectors. The effect does not exist in the South American sector and in the polar caps of both hemispheres.

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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