MESOSPHERIC STANDING WAVES NEAR SOUTH-POLE

Optical measurements of mesospheric winds near South Pole, during Augu st 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 zon al wavenumber-one oscillation with a westward phase progression was al so observed. The direction of the observed mean wind has changed nearl y 60 degrees westward from the typical wind direction observed during the same month in previous years. The direction of the presently obser ved mean wind is nearly parallel to wind direction of the 51.3-hr stan ding oscillation, suggesting an interaction between the mean wind fiel d and the wave during this observation. Based on the simultaneous obse rvation at Scott Base of an uncommon wave with 11.53-hr periodicity wi th short (similar to 20 km) vertical wavelength of propagation, the 11 .6-hr wave observed from South Pole can be identified as a zonal waven umber one inertio-gravity mode of oscillation. Because of the transien ce of this wave and its closeness to-the inertial period, we also disc uss another approach to the interpretation of such waves as possible f orced oscillations.