A Critical Review of the Australian Experience in Cloud Seeding

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From 1947 to 1994 a number of cloud-seeding experiments were done in Australia based on the static cloud-seeding hypothesis. A critical analysis of these successive cloud-seeding experiments, coupled with microphysical observations of the clouds, showed that the static cloud-seeding hypothesis is not effective in enhancing winter rainfall in the plains area of Australia. However, there is evidence to suggest that cloud seeding is effective for limited meteorological conditions in stratiform clouds undergoing orographic uplift. In particular, two successive experiments in Tasmania show strong statistical evidence for rainfall enhancement when cloud-top temperatures are between −10° and −12°C in a southwesterly stream. The evidence for similar effects on the Australian mainland is more controversial. In the summer rainfall regions of northern Australia, the extreme rainfall variability makes it impossible to design a statistical experiment that can to be evaluated in a reasonable time using currently available techniques. Rainfall enhancement in these regions remains inconclusive.

*CSIRO Division of Atmospheric Research, Aspendale, Victoria, Australia.

+CSIRO Division of Radiophysics, Epping, New South Wales, Australia.

Corresponding author address: Dr. Brian F. Ryan, Division of Atmospheric Research, CSIRO, Aspendale, VIC 3195, Australia. E-mail: bfr@dar.csiro.au

From 1947 to 1994 a number of cloud-seeding experiments were done in Australia based on the static cloud-seeding hypothesis. A critical analysis of these successive cloud-seeding experiments, coupled with microphysical observations of the clouds, showed that the static cloud-seeding hypothesis is not effective in enhancing winter rainfall in the plains area of Australia. However, there is evidence to suggest that cloud seeding is effective for limited meteorological conditions in stratiform clouds undergoing orographic uplift. In particular, two successive experiments in Tasmania show strong statistical evidence for rainfall enhancement when cloud-top temperatures are between −10° and −12°C in a southwesterly stream. The evidence for similar effects on the Australian mainland is more controversial. In the summer rainfall regions of northern Australia, the extreme rainfall variability makes it impossible to design a statistical experiment that can to be evaluated in a reasonable time using currently available techniques. Rainfall enhancement in these regions remains inconclusive.

*CSIRO Division of Atmospheric Research, Aspendale, Victoria, Australia.

+CSIRO Division of Radiophysics, Epping, New South Wales, Australia.

Corresponding author address: Dr. Brian F. Ryan, Division of Atmospheric Research, CSIRO, Aspendale, VIC 3195, Australia. E-mail: bfr@dar.csiro.au
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