Optical measurements of mesospheric winds near South Pole, during August 1996, show the presence of large-scale standing waves with periods of 51.3-hr and 107-hr, respectively. In addition, a 11.6-hr period zonal wavenumber-one oscillation with a westward phase progression was also observed. The direction of the observed mean wind has changed nearly 60¿ westward from the typical wind direction observed during the same month in previous years. The direction of the presently observed mean wind is nearly parallel to wind direction of the 51.3-hr standing oscillation, suggesting an interaction between the mean wind field and the wave during this observation. Based on the simultaneous observation at Scott Base of an uncommon wave with 11.53-hr periodicity with short (~20 km) vertical wavelength of propagation, the 11.6-hr wave observed from South Pole can be identified as a zonal wavenumber one inertio-gravity mode of oscillation. Because of the transience of this wave and its closeness to the inertial period, we also discuss another approach to the interpretation of such waves as possible forced oscillations.¿ 1997 American Geophysical Union