Polarization Measurements and Source Locations of Saturn Electrostatic Discharges During the Voyager Era

Abstract A Saturn Electrostatic Discharge or SED is an intense electromagnetic impulse induced by Saturn lightning, which escapes into space through the magnetoplasma of the ionosphere. Since previous SED polarizations from Voyager data are inconclusive, this polarization study is the first which properly considers the characteristics of the Voyager Planetary Radio Astronomy (PRA) instrument and the change of the antenna response as a function of spacecraft attitude. SED radio observations of the Cassini spacecraft from 2004 to 2017 showed a hemispheric dependence of their circular polarization sense at frequencies below 2 MHz, which can be explained by left‐hand ordinary mode emissions. Here we reinvestigated the SED polarizations of the Voyager radio observations at frequencies below 1.3 MHz. As a result, we found mixed polarizations and a dominance of right‐handed polarization, which is difficult to interpret in view of the Cassini result. However, we found that SEDs incident at large angles to the antenna plane (elevation angle ) showed a dominance of the expected left‐handed polarization. We show detailed results of the SED polarization analysis and also compare them with model simulations of the Voyager PRA signal processing of short SED‐like pulses. An equatorial SED source was suggested by its occurrence periodicity for both Voyagers, but imaging observations clearly detected convective clouds at 35N latitude. We demonstrate with Cassini data that the so‐called over‐the‐horizon effect can mimic an equatorial periodicity, even when the single SED source is at 35N latitude. For Voyager 2 also equatorial clouds were imaged.