Unusual SuperDARN backscatter associated with extreme red aurora observed during the May 11, 2024 super storm

A geomagnetic super storm, one of the largest in this solar cycle, was launched on May 10, 2024, producing spectacular auroral displays that could be observed across the continental United States (US) at middle and low latitudes. In this study, we focus on a brief 20-minute interval during the peak of the storm when intense low-energy precipitation and red aurora associated with a substorm auroral breakup were reported over the eastern sector of the US. This strong low-energy precipitation event occurred in the field-of-view of the Blackstone (BKS) Super Dual Auroral Radar Network (SuperDARN) radar which observed strong near-range ionospheric backscatter across its field-of-view. We analyze the elevation and virtual height characteristics of the backscatter to show that the BKS radar observes F-region backscatter at unusually close ranges (< 750 km) during the precipitation event interval. In addition, we note that BKS observes ionospheric backscatter over a broad range of elevation angles, including very high ones. It is likely not physically realistic to support that all the radio waves, launched over a broad range of elevation angles, refract to become perpendicular to the B-field. We therefore interpret that some of these backscatter is produced by irregularities that are not field-aligned. These observations are in agreement with previous theoretical studies suggesting that intense soft electron precipitation can lead to the generation of non field-aligned irregularities which can produce high aspect angle coherent backscatter.