Marvelous results from the HF campaign performed on November 2015 at Arecibo Observatory. “We have performed an experiment to compare as directly as realizable the ionization production rate by HF radio wave energy versus by solar EUV.” This paper shows that radio-frequency production of artificial ionospheres is possible at mid-latitudes in a similar efficiency as high latitudes. This paper open the possibility to study the role of electron acceleration in the space plasma energy redistribution.

Gyroline is observed and investigated theoretically and experimentally... The analysis is supported by range-resolved incoherent scatter spectrograms measured recently at Arecibo... The sensitivity of the Arecibo Observatory was prerequisite for this study. Read More

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