Conventional forecasting of high-frequency (HF, 3-30 MHz) radio wave propagation is based on a combination of ionospheric and propagation models. However, at very high latitudes this approach is seriously undermined by the intrinsically dynamic ionospheric conditions regularly perturbed by energetic particle precipitations and strong electric fields. From this perspective, the multi-year observations of HF propagation characteristics by SuperDARN radars across auroral and polar cap regions represent a unique opportunity for systematic validation of the conventional approach, as well as for creating an empirical propagation model directly from the radar observations. Qualitative identification and quantitative characterisation of the propagation modes requires an accurate knowledge of the vertical angle of arrival (elevation angle) across the high-latitude part of the radar network. This information has become available only in recent years, facilitated by the development of reliable data-based calibration techniques for SuperDARN interferometry. We present the solar-cycle/seasonal/diurnal climatology of HF propagation characteristics at very high latitudes derived from two-frequency observations by the Rankin Inlet SuperDARN radar.

We present three events where high-resolution electric and magnetic field measurements from the Swarm satellite constellation coincided with excellent F-region ionospheric coverage from SuperDARN. Large-scale ionospheric convection patterns from SuperDARN, together with field-aligned-current patterns from AMPERE, provide information on quasi-static ionospheric dynamics traversed by Swarm. Because the Swarm observations and orbital path coincided with favorable SuperDARN/AMPERE observing conditions, it was possible to filter the Swarm electric field observations into a quasi-static component that agreed with the SuperDARN electric field. We contend that the residual electric field from Swarm is thus indicative of small- and mesoscale dynamics not captured by the convection and FAC patterns. We compare calculations of the Poynting flux between the different instruments and show that dynamics on small- to mesoscales can be highly variable within structures like field-aligned currents. In the events shown, small- and medium-scale Poynting fluxes occasionally dominate over that from large-scale processes.

Super Dual Auroral Radar Network (SuperDARN) consists of more than 30 monostatic high-frequency (HF, 10-18~MHz) radars which utilise signals scattered from decameter-scale ionospheric irregularities for studying dynamic processes in the ionosphere. By combining line-of-sight velocity measurements of ionospheric scatter echoes from radars with overlapping fields of view, SuperDARN provides maps of ionospheric plasma drift velocity over mid and high latitudes. The conventional SuperDARN radars consecutively scan through sixteen beam directions with dwelling time of 3.5 s/beam, which places a lower limit of one minute to sample the entire field of view. In this work we remove this limitation by utilizing advanced capabilities of the recently developed Borealis digital SuperDARN radar system. Combining a wide transmission beam with multiple narrow reception beams allows us to sample all conventional beam directions simultaneously and to increase the sampling rate of the entire field of view by up to sixteen times without noticeable deterioration of the data quality. The wide-beam emission also enabled the implementation of multistatic operations, where ionospheric scatter signals from one radar are received by other radars with overlapping viewing areas. These novel operations required the development of a new model to determine the geographic location of the source of the multistatic radar echoes. Our preliminary studies showed that, in comparison with the conventional monostatic operations, the multistatic operations provide a significant increase in geographic coverage, in some cases nearly doubling it. The multistatic data also provide additional velocity vector components increasing the likelihood of reconstructing full plasma drift velocity vectors.

Prior to use in operational systems, it is essential to validate ionospheric models in a manner relevant to their intended application to ensure satisfactory performance. For Over-the-Horizon radars (OTHR) operating in the high-frequency (HF) band (3-30 MHz), the problem of model validation is severe when used in Coordinate Registration (CR) and Frequency Management Systems (FMS). It is imperative that the full error characteristics of models is well understood in these applications due to the critical relationship they impose on system performance. To better understand model performance in the context of OTHR, we introduce an ionospheric model validation technique using the oblique ground backscatter measurements in soundings from the Super Dual Auroral Radar Network (SuperDARN). Analysis is performed in terms of the F-region leading edge (LE) errors and assessment of range-elevation distributions using calibrated interferometer data. This technique is demonstrated by validating the International Reference Ionosphere (IRI) 2016 for January and June in both 2014 and 2018. LE RMS errors of 100-400 km and 400-800 km are observed for winter and summer months, respectively. Evening errors regularly exceeding 1,000 km across all months are identified. Ionosonde driven corrections to the IRI-2016 peak parameters provide improvements of 200-800 km to the LE, with the greatest improvements observed during the nighttime. Diagnostics of echo distributions indicate consistent underestimates in model NmF2 during the daytime hours of June 2014 due to offsets of -8° being observed in modelled elevation angles at 18:00 and 21:00 UT.

The Super Dual Auroral Radar Network (SuperDARN) currently consists of more than thirty high-frequency (HF, 3–30 MHz) radars covering mid-latitude to polar regions in both hemispheres. Their major task is to map ionospheric plasma circulation which provides information about the interactions between the solar wind and the near-Earth’s space plasma environment. One of the major factors defining radar data quality is the signal-to-noise ratio (SNR), which requires an accurate characterisation of the HF noise. The standard SuperDARN data analysis software uses the SNR as part of a set of empirical procedures designed to remove low-quality data from further analysis. In this study we found that the currently used empirical algorithm systematically underestimates the noise level by up to 40%. Based on comparison of theoretical and observational noise statistics, we resolve this issue by designing and validating a procedure for accurate background noise level estimation. We then propose a simple SNR threshold to replace the existing criteria for excluding low-quality data. In addition, we show that several aspects of the radar operational regime design, as well as short-lived anthropogenic radio interference, can adversely affect the quality of the noise estimates at selected radar sites, and we propose ways to mitigate these problems.

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 HF 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 measured at Resolute Bay by the CADI ionosonde and incoherent scatter radars RISR-N/C. We show that the occurrence rate increases with NmF2 roughly linearly up to about ~4·1011 m-3, and the trend saturates at larger NmF2. One expected consequence of this relationship is correlation in seasonal and solar cycle variations of the GS echo occurrence rate and NmF2. 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 Japanize 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.