Calculating the acoustic and internal gravity wave dispersion relations in Venus's supercritical lower atmosphere

The growing interest in studying Venus's interior acoustically from its atmosphere requires understanding how sound propagates through it. The extreme pressure and temperature at Venus's surface correspond to supercritical conditions in the planet's deep atmosphere. Under these conditions, fluids have unique properties that are not accounted for by the widely used ideal-gas equation of state (EoS). Hence, an appropriate real-gas EoS must be used to study the acoustic properties, dynamics, and thermodynamics in Venus's lower atmosphere. This study introduces a methodology for incorporating the Peng-Robinson EoS with the fluid dynamics equations to investigate the fundamental properties of acoustic and internal gravity waves in Venus's supercritical lower atmosphere. Results show that the acoustic cutoff frequency and buoyancy frequency in Venus's deep atmosphere are both lower than on Earth. Additionally, a real-gas potential temperature expression is derived, and a discussion about its use to estimate the atmosphere's stability is presented. Specifically, it is shown that neither the ideal-gas nor real-gas potential temperature expressions can adequately estimate Venus's atmospheric stability. The presented characterizations of acoustic and internal gravity waves in Venus's low atmosphere will be useful in later efforts to discriminate and interpret various waves detected by high-altitude sensors.