Low Frequency Extensions of Cyclotron Maser Instability‐Generated Radio Emission: A Statistical View From Cassini at Saturn

Abstract

The Cassini spacecraft spent 13 years orbiting Saturn, quasi‐continuously measuring Saturn's radio emissions. One of the key elements of the radio spectrum at Saturn is the Saturn Kilometric Radiation (SKR), and several studies have been written on events called Low Frequency Extensions (LFEs) which represent strong, continuous extensions of the SKR down to lower frequencies. A previous machine learning approach, trained on LFEs observed by Cassini, returned several thousand LFEs across the entire mission. We joined events with very short ( minutes) inter‐event separation to produce a data set of 4553 individual LFEs. We find the events have a median duration of 5.65 hr, with a long‐tail distribution up to several days, and thus we separate them into “short” ( hours or planetary rotation) and “long” events for subsequent analysis. We show several formats of spatial maps of LFE location, and these indicate a broad clustering of LFEs in the post‐midnight region of hr local time (LT). Averaged spectrograms illustrate the median morphological shape of LFEs as a function of LT and latitude. Key features such as the broadening of the emission near dawn, and the extinction of the signal at highest latitudes can be clearly seen in these visualizations. Comparison of the start times of LFEs with the Planetary Period Oscillation (PPO) northern and southern phases reveals an organization by phase consistent with the physical picture of preferential viewing when the plasma sheet was thinned, if appropriate phase propagation delays are accounted for.