Saturn Electrostatic Discharges during the Voyager era

Saturn Electrostatic Discharges or SEDs (first detected by the Voyager spacecraft) are electromagnetic radio emissions caused by lightning discharges in Saturn's atmosphere. Previous studies suggested that the SEDs originated from the equatorial region where the rotation period of the atmosphere could explain the periodicity observed in SED activity. However, there were no convective clouds detected around the equator by the optical camera onboard Voyager 1. Recently, the SED radio observations of the Cassini spacecraft from 2004 to 2017 showed that the SEDs are produced by convective storms in Saturn's atmosphere, and the polarization of SEDs is directly linked to the hemisphere of the storm (left-handed SEDs propagated to Cassini from the North, right-handed from the South). Here, we apply a new calibration method to the Voyager radio polarization data, for which we expected to see predominantly left-handed polarization, matching the characteristics of radiation coming from convective storms in the northern hemisphere. We propose that the storm is located at 35° North, where the convective clouds were seen from the Voyager optical cameras. The shorter periodicity of  SED occurrence  in the Voyager data is the result of the relative motion between Saturn's atmosphere and the spacecraft, and the additional effect of radio waves being bent over the horizon in Saturn's ionosphere. This new feature of SED propagation was not known during the Voyager era, but it was observed many times by the orbiting Cassini spacecraft that the over-the-horizon effect can mimic a shorter (or longer) periodicity by shifting the sub-spacecraft western longitude range when the SEDs are observed. In this presentation, we show our new results and interpretations on the SEDs during the Voyager era.

References:
Imai, M., Fischer, G., Taubenschuss, U., Kolmašová, I., Santolík, O., & Píša, D. (2026). Polarization measurements and source locations of Saturn electrostatic discharges during the Voyager era. Journal of Geophysical Research: Planets, 131, e2025JE009079.
https://doi.org/10.1029/2025JE009079