Statistics of Water-group Band Ion Cyclotron Waves in Saturn's Inner Magnetosphere Based on 13 yr of Cassini Measurements

Abstract

Based on Cassini observations from 2004 to 2016, we perform a comprehensive analysis of the statistical distribution of the occurrence rate, averaged amplitude, wave normal angle (WNA), ellipticity, and power spectral intensity of ion cyclotron waves in Saturn's inner magnetosphere. Our results show that ion cyclotron waves mainly occur between the orbits of Enceladus and Dione near the equatorial region (∣λ∣ < 20°), with higher occurrence rates in the northern hemisphere than the southern hemisphere. The averaged wave amplitudes vary between 0.1 and 2 nT with a strong day–night asymmetry and a pronounced minimum at the equator. Saturnian ion cyclotron waves are predominantly left-handed polarized with small WNAs near the equator and become linearly polarized with larger WNAs at higher latitudes. The major wave power occurs frequently at frequencies of 0.5–1.2 , where is the equatorial gyrofrequency of H2O+ ions, with the strongest intensity (>∼10 nT2 Hz−1) at L ∼ 6.5 statistically present in the midnight sector.