Growth of ion cyclotron waves in saturnian magnetosphere in the presence of parallel AC field for ring distribution

Abstract

The Cassini spacecraft observed electromagnetic ion cyclotron waves in Saturn’s inner magnetosphere. EMIC waves have frequencies close to the frequency of water-group ions, they are left-handed, and, in most areas, they propagate to the ambient magnetic field at small angles. Their origins are explained by the ion cyclotron instability generated by the water group ions extracted from Saturn’s neutral clouds. These waves propagate no more than 5° at an oblique angle to the magnetic field. These fluctuations can be identified as the n = 2 mode resulting from the ring distribution of the picked-up ions. In this work, we studied the characteristics of these waves. We also use kinetic method analysis to assess growth rates. The results obtained for the demonstration values of the parameters suitable for the Saturn magnetosphere have been calculated and discussed. It is assumed that temperature anisotropy is an additional free energy source for ion cyclotron instability. Regardless of the magnitude, the AC frequency can significantly affect the growth rate. The drift velocity also seems to affect the growth rate. This result is important to explain the VLF emissions observed over a wide frequency range.