Global Distribution of Electrostatic Electron Cyclotron Harmonic Waves in Saturn's Magnetosphere: A Survey of Over‐13‐Year Cassini RPWS Observations

Abstract

Abstract Based on the measurements from Radio and Plasma Wave Science instrument onboard the Cassini spacecraft over 13 years, we perform a statistical analysis of electron cyclotron harmonic (ECH) wave spatial distribution in Saturn's magnetosphere. The wave occurrence rates, amplitudes, and peak frequencies as functions of magnetic local time, L ‐shell, and magnetic latitude are investigated in detail. Our results confirm that the fundamental band ECH waves mainly occur near the magnetic equator (| λ | < 5°) and also at high latitudes (20° < | λ | ≤ 40°), with averaged amplitudes of about 0.01–0.1 mV/m. By comparison, the amplitudes and occurrence rates of higher harmonics n decrease significantly, and the higher harmonic bands tend to occur at lower L ‐shells along with the enhanced day‐night asymmetry. Overall, Saturnian ECH emissions are preferentially a nightside phenomenon and exhibit a gap in the midlatitude regions (5° < | λ | ≤ 20°) for the occurrence rates. The occurrence rates of ECH waves are higher at high latitudes than those near the magnetic equator, but the statistically averaged amplitudes of high latitude emissions are relatively weaker. Furthermore, the averaged peak frequencies of each ECH wave harmonic band are generally below ( n + 1/2) f ce and have the smallest deviation from ( n + 1/2) f ce near the equator. These results can be readily adopted as representative inputs to quantify the electron scattering effect of multi‐harmonic Saturnian ECH waves and investigate the underlying contribution of ECH emissions to the evolution of the Saturnian radiation belt.