Impact of geometry on 1D molecular-kinetics simulations of acoustic-gravity wave propagation into the exosphere

TL;DR

This study shows that the geometry of wave propagation models significantly affects the estimated heating of a Mars-like atmosphere, with radial models indicating less heating than Cartesian models due to geometric spreading effects.

Contribution

The paper demonstrates that incorporating planetary curvature in DSMC simulations reduces predicted wave-driven heating compared to Cartesian models, highlighting the importance of geometry in atmospheric modeling.

Findings

Radial geometry reduces wave-driven heating by 40-56%.

Wave amplitude growth is attenuated in radial models.

Cartesian models may overestimate heating by factors of 1.7-2.3.

Abstract

Direct Simulation Monte Carlo (DSMC) calculations of acoustic gravity wave propagation into the exobase region of a Mars-like atmosphere reveal that radial geometry can reduce wave-driven heating compared to a Cartesian model. We examine two acoustic wave (AW) modes with periods of 11 minutes (AW1) and 5.5 minutes (AW2) propagating from 100 to 320 km altitude using a radial molecular kinetics model. The wave-driven heating was reduced by 40-56% with cycle-averaged temperature gradient $\langle dT/dr \rangle$ decreasing from 9.4 K per scale height H0 to 5.6 K/H$_0$ for AW1 and from 4.4 K/H$_0$ to 1.9 K/H$_0$ for AW2 when accounting for planetary curvature. While the growth in wave density amplitude was attenuated for the 1D radial geometry as well, the heating differences are more pronounced, with both effects driven by geometric spreading accumulating as waves propagate into increasingly rarefied regions. These findings suggest that accounting for curvature effects is crucial when conducting DSMC estimates of acoustic wave contributions to thermospheric heating and atmospheric escape, as Cartesian-based derived counterparts may be overestimated by factors of 1.7-2.3 for these frequencies.