Nonmigrating tides inferred from the Mars Odyssey and Mars Global Surveyor aerobraking data

Abstract

We analyzed Mars Odyssey (ODY) and Mars Global Surveyor (MGS) accelerometer density retrievals in narrow local‐time (LT) bands during their respective aerobraking phases to study the large‐scale longitudinal density variations in the Martian upper atmosphere. The ODY data and three seasons of MGS data (fall, winter, and spring) all displayed large zonal variations in density (especially wave‐2 and 3) with little vertical phase variation, consistent with previous studies using MGS aerobraking data. The large‐scale density structures were most likely nonmigrating tides sampled at specific LTs. The wave‐2 modes observed in the ODY and MGS data were approximately out of phase, and their respective LT samplings were approximately 12 hours apart. This reinforces the conclusion from previous studies that this mode is most likely an eastward‐propagating diurnal Kelvin wave of zonal wave‐1, which is produced by the interaction of the diurnal thermal forcing and the wave‐2 component of the Martian topography. We also note a close association of enhanced gravity wave variances with the strong longitudinal variations in the large‐scale densities, suggesting the possibility of tidal filtering of the gravity wave (GW) field.