On the probability distributions of SuperDARN Doppler spectral width measurements inside and outside the cusp

The Doppler spectral width of backscatter from the SuperDARN HF radars has been routinely used to identify the ionospheric cusp. The probability distribution of spectral width values has been described as Gaussian ( normal) in the cusp and exponential equatorward of it. Here we re-examine the empirical distributions and show that they are better described by a log-Levy distribution in both the cusp and non-cusp regions, with the same Levy index a approximate to 1.85 but varying Levy location parameter. The spectral width distribution may also be log-Levy at other magnetic local times, but with generally different parameters.