Expert eye on the sky

CLOUD expert Christina Nebel has been making Tasmanian skies rain for the past 20 years.

Mrs Nebel is one of nine cloud seeding officers who takes to the skies from May to October in search of the perfect clouds that can be seeded with silver iodide to prompt rain.

These officers are constantly rostered to monitor the weather and look for suitable cloud seeding conditions, day and sometimes night.

Last year 12 seeding flights were taken during that period with 1.9 kilograms of silver iodide released, compared with 26 seeding flights taken in 2010 with 8.1 kilograms released.

Mrs Nebel said every day in the sky was different.

``We have a lot of instruments on board the aircraft which measure atmospheric conditions, temperature, how much water or ice is in the clouds . . . this is all recorded while we fly,'' Mrs Nebel said.

``When we find the suitable conditions we then light our (silver iodide) burners.''

Suitable clouds include cumuliform and stratiform clouds that must have between minus 5 and minus 10 degree temperatures.

``For rain to form you need ice nuclei (ice crystals) and the silver iodide mimics the ice crystals to help the natural process.

``If there are a lot of ice crystals it is generally not worth seeding but super cold clouds with not many ice crystals are (suitable).''

Eventually when these ice crystals fall and melt, they create more rain.

Mrs Nebel said an officer needed a good stomach for this type of work, for instance when the planes flew through bumpy clouds.

She said there were also some dangers, all of which are handled by various mechanisms on the specialised plane.

``We fly through clouds which are quite wet and cold and one of the largest dangers is that ice can build up on the aircraft so that it gets heavy and can't fly anymore,'' she said.

``The propellers are heated so the ice doesn't build up so quickly, and the wing tips have got expandable rubber on them so whenever the ice build up they can be expanded so the ice will break off.  You can actually hear the ice falling off.

``If (this is not enough) then we have to fly below the freezing level to melt the ice . . . the general procedure for this is to fly out to sea so we can go as low as 500 to 1000 feet.''

Mrs Nebel said there would generally be the pilot, one officer and perhaps a training officer on board every flight.

She said it was quite a busy atmosphere on board, with officers interacting with on board equipment constantly.

``You are monitoring, and communicating with the pilot on where you want to go . . . most people quite enjoy the work.''

Large cumulus clouds over the Midlands in spring 2001 ... the largest of these clouds are already showing signs of glaciation on the left. Picture: HYDRO TASMANIA

Large cumulus clouds over the Midlands in spring 2001 ... the largest of these clouds are already showing signs of glaciation on the left. Picture: HYDRO TASMANIA

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