Quick Dips

Snow Business

Snowmaking is not left up to Mother Nature these days, with the business -- and science -- of snow production firmly in the hands of field managers and their staff.

All the skiers see are the snowguns sitting like oversized hairdriers lying dangerously close to their favourite runs. If the guns are working during the day, all the casual observer notices is water being blown through nozzles and past giant fans. But after the skiers have headed home, the snowmaking teams begin their day.

Traditionally snowmaking has focused on many factors including water, air, ambient temperature, wind velocity, wind direction, relative humidity and pressure airflow rate.

Recent research has analysed the physics of freezing within the snow plume and its microclimate. Because this microclimate is very different from the surrounding conditions, this research has led to the practical benefits of better snow and reduced costs.

Tony Robinson of the National Institute of Water and Atmospheric Research (NIWA) says four additional variables have been under study: wet bulb temperature, nucleation temperature, droplet size and evaporation.

As far as the snowmaking teams go, the wet bulb temperature is the one they have to watch. They get regular printouts from NIWA as snow can only be made when the wet bulb temperature is at -3^oC or less.

"The temperature of a water droplet leaving a snowgun nozzle is between 1^oC and 7^oC. Once released into the air, the water droplet temperature falls rapidly due to the combination of negative expansion, convective cooling and evaporative processes.

"The temperature of the droplet will continue falling until equilibrium is reached and the temperature of the droplet is equal to ambient temperature. This is the wet bulb temperature," Robinson says.

At Rainbow Skifield in Marlborough, a dedicated team of three races around through the night to create perfect snow for skiers. When all seven guns are working together, 1,000 litres of water per minute is pumped from a tarn above the skifield. The team are kept busy, especially on windy days, de-icing the fans and nozzles with blow torches. And if conditions are not right, all that results is water -- not good for skiing on!

Kate Batten, Blenheim