AN INVESTIGATION OF THERMAL TIDAL OSCILLATIONS IN THE EARTH'S ATMOSPHERE USING A GENERAL CIRCULATION MODEL

Abstract

An investigation of tidal oscillations in the earth's atmosphere has been made using an 18 vertical level, hemispheric general circulation model. This approach permitted these tides to be investigated without resorting to linearization of the governing differential equations, as is required by the conventional approach. In addition, it allows the tides to be studied in relation to a realistic atmosphere, and thus in their actual roles as small perturbations, at least in the lower atmosphere, on the basic meteorological fields. Day-to-day surface pressure variations in good agreement with observation were produced by the model, the diurnal and semidiurnal pressure amplitudes and phases also being close to the observed values. An investigation into the excitation mechanism of the oscillation gave results supporting previous work in attributing the dominant cause of the tides to absorption of solar radiation by water vapor and ozone in the atmosphere. Contrary to previous studies, water vapor was found to be of primary importance in exciting both the diurnal and semidiurnal oscillations in the model atmosphere. Generally speaking, the tidal wind and temperature variations obtained were also in agreement with observation and other theoretical work.