Atmospheric Tides at High Latitudes in the Martian Upper Atmosphere Observed by MAVEN and MRO

Global-scale waves have been seen throughout the Martian atmosphere and can achieve significant amplitude at higher altitudes. Previous observations of the upper atmosphere have also revealed wavenumber-3 signatures with significant amplitudes that have been interpreted as signatures of diurnal and semidiurnal tides or stationary planetary waves. This study focuses on two intervals during which concurrent observations of the upper thermosphere made in situ, the middle thermosphere made remotely, and the middle atmosphere made remotely provide observations of the atmospheric tides between 50- and 200-km altitude. Focusing on high latitudes, these observations are able to identify strong wavenumber-3 signatures in the thermosphere that propagate eastward with increasing local time, consistent with an eastward propagating tide. A complementary analysis of the data from the middle atmosphere reveals wavenumber-3 signatures that move eastward and upward. During the first interval, these analyses reveal a combination of the diurnal tide DE2 and the semidiurnal tide SE1 to be present, while during the second only the semidiurnal SE1 is seen. During both intervals, the observations provide a consistent picture of these waves being present from the middle atmosphere to the upper thermosphere, consistent with the theory that such waves are generated in the lower atmosphere and propagate upward throughout the entire atmosphere. Plain Language Summary Previous observations of Mar's atmosphere have shown global-scale oscillations around the planet that impact pressure, temperature density, and composition. The origin of these oscillations is believed to be waves in the atmosphere. These oscillations have been seen in data from near the surface up to altitudes of several hundred kilometers. Observations at lower altitudes have been able to identify the nature of the underlying atmospheric wave, but observations and simulations at higher altitudes have not done so conclusively from the observations alone. Prior studies have suggested that waves with a period of one Mars day, a half Mars day, or stationary wave features could explain the oscillations focused on in this study. Using observations from two time periods at high latitudes, one in the Southern Hemisphere and one in the northern hemisphere, this study identifies one period during which a mix of waves with one Mars day and a half Mars day are present, and one during which only the wave with a half Mars day is observed. A comparison of observations taken in the middle atmosphere with those in the upper atmosphere reveals a consistent picture of the same waves present across this broad altitude range. These results agree with earlier simulations and provide the observational confirmation of those earlier results.