Factors determining spectral width of HF echoes from high latitudes

Spectral width is one of the standard data types produced by the Super Dual Auroral Radar Network (SuperDARN). A pronounced latitudinal gradient in spectral width has been reported in the literature and is used as an empirical proxy for the ionospheric footprint of the open-closed field-line boundary. In this work we investigated the daytime radar echo properties near the spectral width boundary using a multi-frequency sounding regime. We have found that the relatively large spectral width values ≥150 m/s observed poleward of the boundary are produced by ionospheric irregularities with lifetime τl'10–25 ms, which is essentially independent of the scale size. These irregularities are statistically co-located with low-energy (∼100 eV) electron precipitation, which may play a major role in producing F-region turbulence above 75 MLAT via restructuring the ionospheric plasma on time scales ∼τl .