Optimal F Region Electron Density for the PolarDARN Radar Echo Detection Near the Resolute Bay Zenith

Operation of over-the-horizon radars comprising the Super Dual Auroral Radar Network (SuperDARN) relies on strong ionospheric refraction of high-frequency (HF, f = 10–15 MHz) radiowaves such that in order to provide reliable coverage of a given geographic location, the working frequency has to be optimized with respect to the ionospheric conditions. In this work, joint observations of the Rankin Inlet, Inuvik, and Clyde River PolarDARN/SuperDARN HF radars near the Resolute Bay (RB) zenith, where the incoherent scatter radars that monitored the electron density distribution in the ionosphere, are used to assess the F region peak electron density required for HF echo detection near the RB zenith. We show that the echo occurrence rate increases with the electron density up to N_e ≈ (2 − 3) ⋅ 10¹¹ m⁻³, and above this value, the occurrence rate saturates. Thus, optimum electron density for echo detection exist for every HF radar. The saturation effect is more pronounced for the Clyde River radar whose ranges of echo detection are smallest. The saturation in the dependence is reached at smaller densities for the Inuvik radar whose location is farthest from RB and for lower transmitting frequency of observations for every radar. The data presented suggest that having strong-enough electron density in the ionosphere is the major factor for detection of HF echoes in winter or equinox.