Large amplitude exospheric waves seen in MAVEN NGIMS data

Abstract

<p>We examine high altitude gravity waves in the upper atmosphere of Mars using the data from the Neutral Gas and Ion Mass Spectrometer (NGIMS) on the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, orbiting Mars since late 2014. Since the Martian atmosphere is very thin it is also highly perturbed and the effects of these perturbations are debated. Therefore, on 252 trajectories through the Martian atmosphere large amplitude, high altitude perturbations seen in the NGIMS database are examined. When the perturbations are organized by column density rather than altitude, the perturbations both peak and dissipate at similar column densities. These perturbations also increase the O/CO2 ratio above that measured for orbits without a significant perturbation. To understand this effect, the perturbations are subsequently categorized by location and found to be roughly consistent with wave activity seen lower in the atmosphere. Because the NGIMS data for each perturbation cannot measure the temperature or long term behavior, we simulate wave propagation using a Direct Simulation Monte Carlo (DSMC) model. The results from such simulations suggest that these perturbations are most likely large amplitude acoustic gravity waves, whose high frequency and fast phase speed allow them to propagate into the Martian exosphere, affecting the diffusive separation of species and depositing heat.</p>