By Roger Lambert
Cloud seeding experiments began in Australia a year after the world’s first laboratory trials in the USA in 1946. Cloud seeding is simply a way of attempting to artificially generate additional rainfall from clouds. Seeding operations could involve attempting to produce rain when none would normally fall or working to increase precipitation over a particular area.
Clouds can be seeded in a variety of ways using:
silver iodide particles, which have a crystal structure similar to that of ice particles; or
dry ice pellets, which cool the nearby air far below 0°C; or
a process known as hygroscopic seeding.
Seeding using silver iodide burners, dry ice pellets and hygroscopic flares is done from an aircraft although clouds may also be seeded from the ground using silver iodide generators. From 1947 to 1952, CSIRO scientists used RAAF aircraft (Douglas C-47 Dakota) to drop dry ice into the tops of cumulus clouds. The method worked reliably with clouds that were very cold, producing rain that would not have otherwise fallen. The CSIRO carried out similar trials from 1953 to 1956 in South Australia, Queensland and other States. Experiments used both ground-based and airborne silver iodide generators.
During the late 1950s and early 1960s, CSIRO performed cloud seeding in the Snowy Mountains, on the York Peninsular in South Australia, in the New England district of New South Wales, and in the Warragamba catchment area west of Sydney. Of these four experiments, only the one conducted in the Snowy Mountains produced statistically significant rainfall increases over the entire experiment.
DHA FB.31 Vampire. Surprisingly, one of the RAAF aircraft used in these latter experiments was DHA FB.31 Vampire A79-111. The Vampire was fitted with silver iodide generators under both wings.
Avro Anson. The seeding experiments also involved the use of the CSIRO’s own aircraft, Avro Anson VH-WMA (and others). This aircraft will be the subject of a separate article as it would make for a very colourful and different model.
It should be noted that although there was some success with achieving rainfall from the cloud seeding operations, notably in Tasmania, none of the activities in Victoria, Western Australia, Queensland or New South Wales found that seeding would be an economical, reliable way of increasing rainfall.
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