Tidal motions in the high atmosphere

Previously published data on the semidiurnal variation of ambient pressure and wind speed obtained in the altitude interval from 15 to 130 km with such various sensors as rawinsondes, falling balloons, meteor trail drifts, and chemiluminous gas trails are examined in the contexts of a general model of isallobaric potential flow in the atmosphere and a model of tidal motion. The tidal model determines the variation of the amplitude and phase of the pressure oscillation with height, and, on the assumption that the pressure varies sinusoidally, the isallobaric potential flow model defines explicit relationships between the amplitudes and phases of the pressure and zonal wind oscillations and between the phases of the zonal and meridional wind oscillations. The observed values are compared with those predicted by the model, and it is concluded that the observed wind and pressure data fit an isallobaric pattern with a period of 12 hours and agree for the most part with the specific requirements of a semidiurnal atmospheric tide. In particular, however, the time of maximum of the semidiurnal pressure variation does not correspond to that predicted by present tidal theory.