Predicting the Acoustic Signatures of Saturn's Upper Atmosphere

Abstract

Predictions for the acoustic attenuation coefficient and phase speed as functions of frequency and altitude in Saturn's atmosphere are presented and discussed. The pressure range considered in the study is 1 mbar to 1 bar, in windless and cloudless conditions. The atmospheric composition is represented by the major constituents, namely hydrogen (with its two spin isomers, ortho-H$_2$ and para-H$_2$) and helium. The H$_2$ and He concentrations are assumed constant with respect to altitude; however, non-uniform ortho- and para-H$_2$ profiles are considered. The acoustic wavenumber is obtained by incorporating a viscous, thermal, and internal molecular relaxation effects in a linearized fluid dynamics model. The ambient inputs are vertical profiles of the specific heats, shear viscosity, and thermal conductivity coefficients of the three-component (oH$_2$, pH$_2$, He) mixture, extracted at each pressure-temperature pair. The authors acknowledge funding from NASA-Ames Center for Innovation Fund (CIF).