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.