Occurrence of F region echoes for the polar cap SuperDARN radars

Observations by six Super Dual Auroral Radar Network (SuperDARN) polar cap radars, three in the northern hemisphere and three in the southern hemispheres, are considered to assess F region echo occurrence rates over solar, season, and day cycles and to establish relationship between the echo occurrence rate and the background electron density and plasma flow velocity magnitude. The echo occurrence rate is shown to increase toward the solar cycle maximum, more distinctly on the nightside, consistent with a general trend of the background electron density. Over the last 5 years, the echo occurrence rates decline at a rate of 5-10% per year. The pattern of seasonal and diurnal variations in echo occurrence is found to be consistent with previous SuperDARN publications. Minor dips in echo occurrence rate are observed in winter solstices, and these are related to an overall decrease in the electron density. In most of the time sectors, the echo occurrence rate increases with the electron density but only up to a certain threshold value after which the dependence saturates. The level of the saturation depends on season, local time, and average plasma flow velocity magnitude. For the summer daytime observations, the echo occurrence rate correlates with variations of both electron density and plasma flow velocity magnitude

Visualization of ULF waves in SuperDARN data

Measurements of ionospheric E x B drifts obtained with HF radars from the SuperDARN (Super Dual Auroral Radar) Network sometimes show signatures of ULF (few mHz) waves. We present a new data display technique that facilitates the detection of ULF waves in both ground and sea scatter returns. Statistical study of high time resolution data from the SuperDARN TIGER radar in Tasmania, Australia, revealed that ULF wave signatures occur on an everyday basis with ground scatter accounting for about 60% of wave events. About half of these events exhibit high coherence across large spatial distances and are associated with ULF pulsations recorded by a ground magnetometer. These results show that SuperDARN radars may be used to routinely monitor ULF waves in the high-latitude ionosphere

The role of Pc1-2 waves in spectral broadening of SuperDARN echoes from high latitudes

Previous studies of Super Dual Auroral Radar Network (SuperDARN) echoes from high latitudes have shown large spectral widths (≥200 m/s), which cannot be interpreted in terms of ionospheric drifts. A recent model of André et al. [1999 , 2000a, 2000b] invoked modulation of ionospheric plasma drift velocity by ultra low frequency (ULF) waves within the Pc1-2 band (0.1–5 Hz). Their simulated signal was processed in the same way as real radar echoes, and the output spectral width was much larger than the input signal bandwidth. This was attributed to signal undersampling. After re-examining their model we found that the spectral broadening was caused by the way the signal was simulated. This paper presents a revised model that gives spectral width estimates close to the input signal bandwidth. An alternative explanation of the experimental data involves spatio-temporal non-uniformity of the ionospheric irregularities due to particle precipitation