The Generation of Saturn's Aurora at Lower Latitudes by Electrostatic Waves

Abstract

In the present paper we have modeled diffuse auroral emissions, which have been observed at lower latitudes as compared to the main auroral arc at Saturn. It is generally accepted that these emissions are generated by precipitation of hot population of magnetospheric electrons on the closed field lines. We have considered the pitch angle diffusion by electrostatic electron cyclotron harmonic waves as the mechanism to diffuse trapped electrons into the atmospheric loss cone. Electrons are thereby precipitated into the atmosphere and excite the neutral atmospheric constituents producing auroral emissions. Calculation of ultraviolet emission intensities has been performed at two L-shells 5.35 and 7.0. Observed hot electron distribution functions and observed electrostatic electron cyclotron harmonic wave characteristics have been used in the study. Intensities of Lyman-alpha emission from excitation of atomic H and Lyman-alpha produced from dissociative excitation of H2 have been calculated, obtaining the values 20.1 R (1.8 R) and 1.6 kR (0.29 kR), respectively, for both L-shells 7.0 (5.35).Further, intensities of Lyman and Werner bands of H2 are also calculated. These have the values 7.50 kR (1.43 kR) and 7.52 kR (1.49 kR), respectively, for L-shells 7.0 (5.35). It is observed that the volume excitation rates of these four excitations peak at an altitude of about 2,000 km. From the range-energy relation in H2 gas it is estimated that the electrons producing these excitations should have energies less than about 250 eV. ©2018. American Geophysical Union. All Rights Reserved.