The subauroral polarization streams (SAPS) are latitudinally narrow regions of westward directed flows observed equatorward of the evening sector auroral oval. Previous studies have shown that SAPS generally occur during geomagnetically disturbed conditions and exhibit a strong dependence on geomagnetic activity. In this paper, we present the first comprehensive statistical study of SAPS using measurements from the U.S. midlatitude Super Dual Auroral Radar Network (SuperDARN) radars. The study period spans January 2011 to December 2014, and the results show that SuperDARN radars observe SAPS over a broad range of activity levels spanning storm time and nonstorm conditions. During relatively quiet conditions (−10 nT 

[1] The midlatitude Super Dual Auroral Radar Network (SuperDARN) radars regularly observe nighttime low-velocity Sub-Auroral Ionospheric Scatter (SAIS) from decameter-scale ionospheric density irregularities during quiet geomagnetic conditions. To establish the origin of the density irregularities responsible for low-velocity SAIS, it is necessary to distinguish between the effects of high frequency (HF) propagation and irregularity occurrence itself on the observed backscatter distribution. We compare range, azimuth, and elevation data from the Blackstone SuperDARN radar with modeling results from ray tracing coupled with the International Reference Ionosphere assuming a uniform irregularity distribution. The observed and modeled distributions are shown to be very similar. The spatial distribution of backscattering is consistent with the requirement that HF rays propagate nearly perpendicular to the geomagnetic field lines (aspect angle Ä1 ı ). For the first time, the irregularities responsible for low-velocity SAIS are determined to extend between 200 and 300 km altitude, validating previous assumptions that low-velocity SAIS is an F-region phenomenon. We find that the limited spatial extent of this category of ionospheric backscatter within SuperDARN radars' fields-of-view is a consequence of HF propagation effects and the finite vertical extent of the scattering irregularities. We conclude that the density irregularities responsible for low-velocity SAIS are widely distributed horizontally within the midlatitude ionosphere but are confined to the bottom-side F-region.

The Super Dual Auroral Radar Network (SuperDARN) is an international collaboration of researchers interested in near-Earth space plasma. This group uses high frequency (HF) radars to measure backscatter from magnetic field-aligned plasma irregularities to study space weather manifested in the Earth's magnetosphere and ionosphere. This paper describes a new antenna design, the twin terminated folded dipole (TTFD), used by the latest generation of SuperDARN radars. The TTFD design provides a less expensive alternative to the log-periodic antenna design previously used by SuperDARN radars. The radiation characteristics of the new antenna are analyzed with modeling results from a version of the Numerical Electromagnetics Code version 2 (NEC2). The TTFD antenna modeling results are then compared to a logperiodic antenna design used for a SuperDARN radar. It is concluded that the less expensive TTFD antenna design is an adequate replacement for the log-periodic antenna based on modeled performance characteristics. The TTFD antenna design demonstrates the ability to generate HF backscatter suitable for scientific analysis. I.978-1-4244-8902-2/11/$26.00 ©2011 IEEE

Super Dual Auroral Radar Network (SuperDARN) radars operate in a coordinated but monostatic configuration whereby high‐frequency (HF) signals scattered from ionospheric density irregularities or from the surface of the Earth return to the transmitting radar where Doppler parameters are then acquired. A bistatic arrangement has been developed for SuperDARN radars in which HF signals transmitted from one radar are received and analyzed by another radar that is separated by a large distance (>1,000 km). This new capability was developed and tested on radars located in Oregon and Kansas. Numerous 3‐day bistatic campaigns have been conducted over a period extending from September 2019 through March 2020. During these campaigns three distinct bistatic propagation modes have been identified including a direct mode in which signals are transmitted and received through the radar side lobes. Direct mode signals propagate along the great‐circle arc connecting the two bistatic radar sites, reflecting from the ionosphere at both E region and F region altitudes. Two additional modes are observed in which HF signals transmitted from one radar scatter from either ionospheric density irregularities or from the surface of the Earth before propagating to the bistatic receiving radar. Ray tracing simulations performed for examples of each mode show good agreement with observations and confirm our understanding of these three bistatic propagation modes. Bistatic campaigns continue to be scheduled in order to improve technical aspects of this new capability, to further explore the physical processes involved in the propagation and scattering of HF bistatic signals and to expand the coverage of ionospheric effects that is possible with SuperDARN.