Evidence for nonmigrating thermal tides in the Mars upper atmosphere from the Mars Global Surveyor Accelerometer Experiment

Abstract

Mars Global Surveyor Accelerometer Experiment density measurements indicate the presence of planetary‐scale wave structure in the Mars upper atmosphere (∼130 km). In particular, Phase 2 aerobraking observations reveal large amplitude zonal wave 2 and 3 variations in dayside density between ±60° latitude. These spatial variations (in a fixed local solar time reference) can be qualitatively reproduced by a Mars general circulation model and are identified as a manifestation of eastward propagating nonmigrating thermal tides with long vertical wavelengths. The simulated wave 2 variation is dominated by a diurnal period wave 1 Kelvin mode while the principal components of the simulated zonal wave 3 structure are a diurnal period wave 2 Kelvin mode and a wave 1 semidiurnal tide. The characterization of these waves is important for understanding the structure and variability of the martian atmosphere at aerobraking altitudes.