Thermal Impacts of Atmospheric Gravity Waves in the Martian Thermosphere

Abstract

Observations of the Martian thermosphere have revealed small-scale, large amplitude fluctuations believed to be associated with atmospheric gravity waves (GWs). Previous analysis of the MAVEN Neutral Gas and Ion Mass Spectrometer (NGIMS) data has described the overall behavior of these waves and their consistency with GW theory. One of the key impacts of these waves as they dissipate is the heating and cooling of the neutral atmosphere, from both deposition of the energy and transporting heat. While initial evidence for this has been presented, systematic patterns in heating and cooling require the analysis of a long-term data set. This study examines 5 years of NGIMS data to systematically determine the thermal impact of GWs in the thermosphere, and variations with location, season and local time. While both viscous heating and cooling from sensible heat flux are significant at the altitudes seen with NGIMS, cooling tends to dominate in the cases examined. Clear variations in the heating and cooling are seen with the background atmospheric density, with a large degree of variability in addition to this, reflecting the high degree of variations in GWs seen in the thermosphere. Seasonal variations in the net thermal impact of GWs are apparent at mid-high latitudes, and less clear near the equator. During times when MAVEN's periapsis is deeper inside the atmosphere, clear increases in the net thermal impact of GWs with altitude are evident. The overall results are consistent with some prior simulations but include altitudes and conditions not reported in those studies.