Lamb waves in the lower thermosphere: Observational evidence and global consequences

Meteor radar observations of hourly neutral meridional winds at 95 km altit ude near 88 degrees S and along the four meridians 0 degrees, 90 degrees E, 90 degrees W, and 180 degrees, were made from Amundsen-Scott Station at So uth Pole from January 19. 1995, through January 26, 1996, and from November 21, 1996, through January 27, 1997. These data reveal the existence of +/- 5-15 m s(-1) oscillations with periods between about 7.5 and 10.5 h, propag ating to the west with zonal wavenumber s = 1. These oscillations are inter preted as the atmospheric manifestations of gravitational normal modes or " Lamb" waves. Barring significant Doppler-shifting effects, the second symme tric mode with period near 8.6 hours, and the first asymmetric mode with pe riod near 10.4 hours, appear to dominate. At middle latitudes, for limited duration time series, it would be easy to confuse these waves with terdiurn al (8 hours) and,semidiurnal (12 hours) solar tides. The Global Scale Wave Model (GSWM) is used to simulate the global perturbation temperature and wi nd fields consistent with these observations. Wind and temperature oscillat ions exceeding 12 m s(-1) and 12 K, and 80 m s(-1) and 40 K, are predicted to occur for the 10.4-hour and 8.6-hour waves, respectively, above 110 km. Such perturbations may be observable by incoherent scatter radars now in ex istence.