Studies were made of the dynamics of the atmosphere at heights of between 65 km and 102.5 km at Birdlings Flat over a period of 2½ years. Variance profiles for internal gravity waves were calculated for each month in the 2½ year period. These profiles were similar for each month. The variances remained reasonably steady in most months at heights below 80 km, but increased steadily above 80 km to a maximum at heights between 92.5 km and 97.5 km. various models were developed to explain this and other features of internal gravity wave behaviour. A simple saturation model explained most of the observed features of internal gravity wave behaviour in this region. The isotropy of internal gravity waves was also considered. Isotropic behaviour was generally observed below 80 km, but strong anisotropies were observed to occur between 80 km and 95 km. These anisotropies occurred in the same direction in every month at all heights between 80 km and 95 km. Above 95 km the anisotropies were less pronounced. Various explanations for this behaviour have been considered, but no explanation has proved to be entirely adequate. Some consequence of this behaviour have also been discussed.