With the arrival of a cold air, a snowfall fell and covered our city with a layer of white fur coat. However, in this cold and freezing environment, one outdoor sport has started to warm up, which is skiing. Put on your ski clothes, put on your ski goggles, step on your skis, and speed down from a high place. The feeling of lightning speed will make people excited. The fun of skiing is self-evident, but how much do you know about the snow that allows us to enjoy this wonderful feeling?
In the cold winter, when people are looking forward to a snowfall, the ski resort has already been covered with snow. Looking around, it is completely white. Where does the snow in the ski resort come from? There are two sources of snow in ski resorts, one is snow made by snowmaking machines, and the other is natural snowfall.
To understand the principles of snowmaking, you must first know how snowflakes are formed.
Snow is made up of snow crystals, also known as snowflakes. Snowflakes are very light. If you pile 10,000 snowflakes together, you can get about 1 gram of snow. To cover a 1,000-meter-long primary ski trail, approximately 18,000 cubic meters of snow is needed. Therefore, if you want to ski, you have to make artificial snow.
Friends who have been to ski resorts may have seen the scene of the snowmaking machine at work. It is like a cannon, blowing snowflakes into the air continuously. The snowmaking machine makes snow, which imitates the formation process of natural snow, which is a physical phenomenon.
The formation of snowflakes is divided into two steps, the first step is nucleation. Under normal circumstances, there are many tiny particles in the air, which are condensation nuclei. They can absorb moisture in the air and form droplets. When the droplets freeze into ice particles, they become the crystal nuclei of snowflakes.
If there are no condensation nuclei in the air, a lower temperature is needed for water vapor to spontaneously liquefy and sublime to form crystal nuclei. After the crystal nuclei are formed, they "grow". Under microscopic conditions, it can be seen that the water molecules in the crystal nucleus are connected to each other and form a hexagonal structure under the action of force. When the temperature is low enough and the water vapor is saturated, the water vapor will continue to condense and crystallize around the crystal nucleus. Therefore, most snowflakes are hexagonal, but due to different "growing environments", the final shapes of snowflakes are also different.
What is the specific process of making snow with a snowmaking machine? First, water is pressurized with a water pump, and then it meets the high-pressure air generated by the compressor in the nucleator, and is blown into the air by a fan to meet cold air, thereby forming crystal nuclei. Finally, the crystal nuclei will combine with the water vapor in the air and slowly grow, creating snow.
Snowfall weather requires not only sufficient moisture, but also the blessing of cold air. Since artificial snowmaking simulates natural snowfall, it means that it will also be affected by meteorological conditions.
Lower air temperatures are conducive to better snowmaking effects. At lower temperatures, moisture in the air condenses into snowflakes more easily, and the resulting snowflakes are lighter, fluffy, and easier to maintain their shape. Therefore, under low temperature conditions, the snowflakes produced by the snowmaking machine are more likely to accumulate on the ground and form a long-lasting snow layer.
Humidity is also a key factor in snowmaking. The lower the humidity, the faster water in the air evaporates and the better snowflakes form. If the humidity in the air is too high, it can cause the snowflakes to become soggy and difficult to maintain their shape. Therefore, when the humidity is reduced, it is more conducive to the formation of snowflakes. Therefore, snowmaking must also choose an environment with low temperature and low humidity.
In addition to meteorological conditions, the water injected into the snowmaking machine also has certain requirements. Water can be divided into surface water, underground water, deep well water and pipeline water according to different storage locations. Although they are all water, relatively speaking, surface water is more affected by weather. When the weather is cold, the temperature of surface water, especially surface water in contact with the air, will also drop rapidly. If temperatures drop below freezing, surface water may freeze.
During the snowmaking process, the lower the temperature of the water injected into the snowmaking machine, the better the snowmaking effect. When the temperature is -3°C, the surface water temperature is closest to 0°C, and the air temperature is low enough at this time that the snow produced is not easy to melt. Therefore, when the temperature drops below -3℃, snowmaking can be started.
Some people say that the snow in ski resorts does not melt, so it can stay soft for a long time, unlike natural snow, which although it looks light, can easily melt into water. So, is this really the case? If not, what is the truth? In fact, both natural and man-made snow can melt.
There are many differences between natural snow and artificial snow. Natural snow is mostly hexagonal. In contrast, the shape of the snow produced by any kind of snowmaking equipment cannot be similar to that of natural snow and cannot achieve a hexagonal shape. Therefore, some people call artificial snow "snowballs".
The two also differ in density. Natural snowflakes are less dense than artificial snow. The density is high and the melting speed is slow. Therefore, under the same conditions, the same volume of artificial snow melts slower than the natural snow.
In addition, the reason why the snow in the ski resort gives people the feeling of "not easy to melt", in addition to the high density of artificial snow, there is another more important reason, that is, the snow in the ski resort is "maintained" every day.
Many people know about car maintenance tools, such as engine oil, engine filter, air filter... But do you know what maintenance tools there are for snow? Snowmaking machines, snow compactors, and snow plows are the "three-piece set" for maintaining snow.
When the temperature is high during the day, some of the snow in the ski resort will melt. At night, the temperature drops and the melted snow will freeze again. It is difficult to control the direction and balance of the body when sliding on icy snow. Therefore, every night, workers use snow plows to plow the snow, just like farmers plow before planting. This can soften the "hardened" snow on the ground. Then a snow cannon will be used to make artificial snow, a new layer of snow will be laid on the soft snow again, and finally a snow compactor will be used to compact the snow.
Even freshly made snow needs to be compacted by a snow compactor. Only when the compacted snow thickness reaches more than 30 centimeters can skiing conditions be achieved.
Generally speaking, the hardness of primary ski trails for novices is 450 kg/cubic meter, and the density of ski trails used for professional competitions will be even higher. The International Ski Federation requires that the surface of alpine skiing trails must maintain a crystalline state similar to that of the ice surface, which is the so-called ice-like snow. Building this kind of snow track requires a series of operations such as water injection and repeated rolling. After that, it needs to be maintained every day.
In addition to the snow trails, weather also has a certain impact on skiing. If you encounter strong winds, such as winds above level 3, people will be unstable and it is not suitable for skiing at this time. When the temperature reaches -16℃--20℃, it is not suitable for long-term outdoor activities; when the temperature reaches -20℃, it is not suitable for outdoor activities, and it is not suitable for open-air skiing. Moreover, a long period of extremely cold weather will cause ice layers to appear on the snow trails, making it easy for people to slip. In addition, it is best to ski in the morning. This is because the ski resort makes snow every night or morning, and the snow in the morning is the best.