D.C. 6 aircraft flying at altitudes between 11,000 and 19,000 feet between Melbourne and Sydney on 7th July, 19540 reported severe turbulence in clear air above cloud with a marked limit of turbulence to the northwest. Various factors favouring turbulence in the atmosphere – hydrostatic instability, Richardson criteria, and terrain are considered and it is shown that the last is the only factor which cannot be eliminated.
A. Garriock (Wed,) studied this question.