Understanding Processes Occurring in the Upper Atmosphere of Mars Using NGIMS Data Analysis
Williamson, Hayley, Engineering Physics - School of Engineering and Applied Science, University of Virginia
Johnson, Robert, EN-Mat Sci/Engr Dept, University of Virginia
Two main processes in the present Martian atmosphere are examined 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. Because of the prediction that Mars atmosphere might have been lost due to its interaction with the solar wind, maps of average atmospheric densities at altitudes of 180-220 km are created using the NGIMS data for three species: O, Ar, and CO2. The density data are averaged and then organized according to the direction of the solar wind convective electric field, which determines the average direction of flow of the solar wind ions. By mapping the average densities, I look for evidence that solar wind ions that penetrate and collide with the neutral atmosphere affect the neutral densities. However, while the data examined suggest there might be a small effect at present, the evidence is not statistically significant. Since the Martian atmosphere is very thin it is also highly perturbed and the effect 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 column densities roughly independent of the time of day. Additionally, these perturbations 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, model simulations of wave propagation are described based on the 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.
PHD (Doctor of Philosophy)
Mars, Planetary Science, Atmospheric dynamics