Mars Global Surveyor (MGS) accelerometer measurements near 125 km [Keating et al., 1998> reveal longitudinal density structures comprised of zonal wavenumbers s=1 and s=2 which are interpreted as stationary waves. An alternative interpretation is that these structures may be nonmigrating tides which appear as quasistationary features due to restricted sampling in local time, and which owe their existence to Mars' topography. One of these oscillations, the diurnal Kelvin wave, is investigated here. It gives rise to density perturbations similar to the measurements. Other nonmigrating tides may also make important contributions. ¿ 2000 American Geophysical Union