Cloud Seeding

Various attempts had been made to artificially stimulate rainfall in Australia and other countries. As mentioned by Gibbs (1975) Clement Wragge sought to break a drought in Queensland by installing six Stiger vortex guns in the vicinity of Charleville in Queensland. It is not surprising that he was unsuccessful because Stiger had used his vortex guns for the purpose of reducing hail damage, a venture which seems more likely to have been successful. My reading of Russian experiments in the 1960s and 1970s aimed at reducing hail damage makes me believe that the shock wave of an explosion is likely to convert super-cooled water drops into ice and thus reduce damage to crops by limiting the size of hailstones.

Encouraged by Len Dwyer, Gerry and I studied the effects of cloud seeding. Gerry looked from a statistical point of view and I scrutinised the theory of the rain process as learnt from Houghton during my time at MIT.

However E. G. (Taffy) Bowen, Chief of the CSIRO Division of Radiophysics and famous for his scientific contributions to the development of radar in the UK during the war, was convinced that cloud seeding was a possible means of reducing the effects of drought in Australia. He was not impressed by our arguments that it would be wise to first study the rain process from a theoretical point of view and to take great care in designing cloud seeding experiments which would permit a statistical evaluation of the success or otherwise of his experiments. He rejected my suggestion that the design of experiments should be carried out jointly with Gerry O'Mahony and that evaluation of results should be carried out by a body wholly independent of his Division. I believed Gerry O'Mahony ideal for such an evaluation, being well qualified to examine statistical significance (especially after his year with Prof Pat Moran at the ANU) and having a meticulous approach when asked to make a scientific judgement.

Bureau of Meteorology