Science in everyday life: The snow falls loudly

The snow is falling loudly

You can go on the skis, even if Mother Hulda doesn't play along.

Winter sports have been enjoying increasing popularity again for a number of years, but the operators of lifts, hotels and other infrastructure are under no illusions: they mainly owe the increase in sales to heavy snowfall in recent winters; however, these have become rare.

Due to global warming, only 85 percent of Swiss ski areas are snow-sure, and the trend is falling. So that the all-important winter tourists don't stay away, the operators of the lift facilities give Mother Holle a helping hand and invest in snow cannons.90 percent of all large ski areas in the Alps are now equipped with them.

In nature, the white splendor is created in clouds at temperatures of minus ten degrees and less. Fine droplets then freeze on tiny floating particles, so-called crystallization nuclei, and form ice crystals that are not even a tenth of a millimeter in size. They combine and eventually float to earth as snowflakes.

Snowmaking machines imitate this process. To do this, they first atomize water into tiny droplets and thus oversaturate the air - a kind of ground cloud is created. However, the droplets inside can only freeze, i.e. give off heat, if part of their water evaporates. This is more difficult when the humidity is high than when it is low. That's why snowmaking works best when the air is dry and the temperatures are as low as possible. Even a humidity of 30 percent requires at least one degree below zero, at 80 percent humidity it must be less than minus four degrees.

The oldest type of snowmaker of this kind usually leads water and compressed air to the cannon via frost-proof pipes underground. The gas pressure of five to ten bar is generated by a central compressor station that can supply several devices. These systems have now been largely replaced by the more efficient propeller cannons.

Nozzles arranged in a ring there atomize the water and a turbine blows the droplets into the air. The principle of the old compressed air cannons has proven itself in the "nucleator nozzles", which contribute the necessary crystallization nuclei: while air compressed by a compressor expands rapidly behind such a nozzle, it extracts heat from the water droplets and ice particles form.

If you expect a little peace and quiet at night during your skiing holiday, you should keep your distance from the piste: a propeller cannon is louder than a truck, high-pressure systems even drown out a jackhammer. There are also snow cannons that run at a reduced turbine speed and then correspondingly quieter. But they also deliver less snow.

Did you know?

In the late 1940s, Canadian researchers studied the effects of frost on jet engines. To do this, they sprayed water into a wind tunnel at low temperatures, but they produced snow. The scientists only registered it as a negative side effect of their experimental setup. It was not until 1950 that Wayne Pierce of the US company Tay Manufacturing in Milford, Connecticut, invented a compressed air snow cannon, and eight years later the American Alden Hanson invented the propeller snow cannon.

• Additional crystallization nuclei in the water enable snowmaking at temperatures above minus three degrees. A processed bacterium called Snowmax has proven particularly effective; when the air is very dry, snow cannons work efficiently even at 0 degrees. This is the naturally occurring Pseudomonassyringae, which is grown in tanks, freeze dried and killed by sterilization.

  Through the use of such substances, the snow guns also require less energy, but their use is banned in many countries such as Germany and Austria because the long-term consequences for nature cannot be reliably estimated.

• Do you want the snow to be wet or dry? Powder snow is ideal for skiing because it doesn't stick to the ski. However, wet and coarse-grained snow is required for a stable base for a slope, because it does not melt or shift as easily. Snow cannons can produce both types by adjusting the water/air ratio and droplet size accordingly.
• At minus 12 degrees Celsius and a relative humidity of 60 percent, a large snow cannon covers a hectare of piste with a 25 centimeter layer of snow in 12 hours. It uses over a million liters of water and, depending on the system, location and water procurement, 8 to 10 megawatt hours of energy, i.e. about as much as two 4-person households a year. The investment costs per hectare are around 140,000 euros.

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