Some ISR facilities observe day time plasma lines (produced by suprathermal electrons energized by the sun). Vierinen et al. [2017] implemented some techniques, using the high sensitivity of the Arecibo ISR system, to observe the night time plasma line. The nighttime plasma line is produced by suprathermal electrons energized by sources different than the sun. No other radar has the sensitivity to implement this technique.

Radio-frequency (RF) auroras, like the beautiful example shown in Figure 1 and the movie (link here), are often dancing across the night skies of Puerto Rico. Unlike their high-latitude cousins, however, these tropical phantasms do not generate optical emission and are not associated with solar activity. These are mid-latitude RF echoes observed with coherent radar and displaying radio signatures similar to those detected from the northern lights. Read More