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

Abstract

Meteor radar observations of hourly neutral meridional winds at 95 km altitude near 88°S and along the four meridians 0°, 90°E, 90°W, and 180°, were made from Amundsen‐Scott Station at South 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, propagating to the west with zonal wavenumber s = 1. These oscillations are interpreted as the atmospheric manifestations of gravitational normal modes or “Lamb” waves. Barring significant Doppler‐shifting effects, the second symmetric mode with period near 8.6 hours, and the first asymmetric mode with period near 10.4 hours, appear to dominate. At middle latitudes, for limited duration time series, it would be easy to confuse these waves with terdiurnal (8 hours) and semidiurnal (12 hours) solar tides. The Global Scale Wave Model (GSWM) is used to simulate the global perturbation temperature and wind fields consistent with these observations. Wind and temperature oscillations 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 existence.