The Blanket Effect is intended for others to learn about weather modification and its related subjects in an easy to understand way. Started in 2005, this blog is a work in progress as the technology advances

January 22, 2007

Snowy Mountains Go Silver (Iodide)

(note: Another perspective is featured on the ongoing cloud-seeding project in Australia, as excerpts from a research paper on the subject are featured below)


Mark Heggli, Barry Dunn, Arlen Huggins, John Denholm, Loredana Angri and Trevor Luk

Investigations over the last 50 years have confirmed the significant precipitation enhancement potential of the Snowy Mountains region of Australia.

During 2004, special legislation (PDF) authorizing Cloud Seeding under very strict conditions was passed in New South Wales.

Trial operations commenced during June 2004, preceding a five year experiment to determine the economic and environmental viability of precipitation in a significant national park estate.

The project infrastructure was constructed and installed over a period of 14 weeks to satisfy time constraints set in the enabling legislation.

Meteorological data and operational experience gained during 2004 has been formative in developing the experimental design and refining equipment and systems requirements for the five year experiment commencing in 2005.

The Snowy Mountains form the highest mountain range in Australia and are located near the border of New South Wales (NSW) and Victoria.

Snowfall over this region is an important source of water for hydro-generation, irrigation and recreation; however historical data indicates that the annual snowpack has decreased by more than 50% over the last 50 years.

The potential and opportunity for seeding winter orographic clouds over the area have been well documented.

The mountain range provides essential lift, with the terrain ascending approximately 1800 m over a rather short horizontal distance of about 15 km.

The atmosphere in the lowest 2 km is the source of vast quantities of condensate supply and associated production of supercooled liquid water.

Australia has been involved in cloud seeding for over 57 years with the first investigations occurring in 1947.

An experiment was carried out in the Snowy Mountains using aircraft during the period 1955-1960, and results from this investigation were extremely encouraging with a measured increase of 19%.

There was an attempt to undertake a cloud seeding experiment in the Snowy Mountains in 1993, however that attempt did not proceed because of environmental and ski industry concerns and a lack of political direction at the time.

The Snowy Mountains Cloud Seeding Trial Act 2004 (NSW) authorizes Snowy Hydro Limited to undertake a six year cloud seeding trial in the Snowy Mountains region of NSW.

The Act was proclaimed on 5 April 2004, and Snowy Hydro commenced cloud seeding operations on 18 June 2004.

The enabling legislation imposes a number of significant conditions on Snowy Hydro including a requirement that:

• Operations must be ground based;
• Only silver iodide be used as the ice nucleating agent;
• No dispersal of seeding agent is to take place from within Wilderness Areas;
• Operations only take place when precipitation would be likely to fall as snow; and
• That cloud seeding operations and their effect must be monitored and reported annually.

In addition, the NSW Government required Snowy Hydro Limited to prepare and implement an environmental management plan prior to commencing operations.

Approximately 40% of the annual cloud seeding budget is allocated to environmental monitoring and compliance.

Over a period of 14 weeks following proclamation of the enabling legislation, Snowy Hydro Limited constructed and installed twelve pairs of ground generators, thirty high-resolution rain gauges, two weather stations and installed upwind and downwind rawinsonde stations, a dual-channel microwave radiometer and an X-band radar.

In addition, three new generator sites are being established, involving relocation of two of the southern most generator sites.

All of the equipment for the project is located within a significant National Park.

Some of the most challenging aspects of the project instrumentation were associated with deployment of infrastructure.

Road access throughout the park is limited, and a quarantine on clearing vegetation required innovative solutions to achieve the desired project outcomes.

It was necessary to raise the burner and shroud assembly above local vegetation so as to launch the aerosol plumes effectively and to avoid potential environmental impact.


The project will use silver iodide as an ice nucleating agent, and indium tri-oxide as the non-nucleating tracer.

A critical issue in the use of trace chemistry in evaluating experiments is to establish and maintain the seeder and tracer particle size and concentrations emitted from the ground generators.

Operation of a number of generators was aborted on several occasions earlier in the 2004 season because of wide variations in solution flow rates caused by temperature variations and degassing of the propellant in the solution lines.

This problem was completely overcome by using computer-controlled valves, operating to maintain a set flow.

During the 2004 season, transmission electron microscope examination of seeder and tracer aerosols confirmed particle sizes and distributions smaller than that reported in the literature required to produce optimal nucleation.


Snow samples were collected from 26 profiling sites during the 2004 season.

Sampling sites were usually accessed by oversnow vehicle, as local conditions typically precluded the safe use of helicopters in post storm conditions.

While the objective was to complete sampling within one day of operations, sampling campaigns extended to three days due to poor weather conditions.

Consequently, data from samples collected after the first day were often of lower quality, as changes in the snowpack start to occur almost immediately.

Results of the 2004 snow chemistry analysis, have confirmed that the primary target and upwind mountain ranges were being seeded effectively during most storm events, both in the concentrations of chemicals monitored and in the silver to indium ratio.

Prevailing winds in seeded storms were predominately from northwest counter-clockwise through southwest.

Recorded silver concentrations were as high as 180 ppt and silver-indium ratios of the order of 20:1
, over the central part of the target area.


Infrastructure for the Snowy Precipitation Enhancement Research Project was fabricated and operational within 14 weeks of enabling legislation being proclaimed by the NSW government in April 2004.

While the legislation enabled the project to proceed, it also imposed rigorous environmental performance obligations on Snowy Hydro, requiring annual surveillance monitoring and reporting to be undertaken.

Approximately 40% of the annual operating budget is allocated to environmental compliance.

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