Why does winter exist, and why is it cold in winter?

Maybe because the inclination angle of light changes or are moving air masses responsible? Probably because we are farther from the Sun? The answer is not in the change of distance, but in the relation of the rotation axis of the Earth and the covered distance around the Sun. In winter, cold is due to a smaller incidence angle of sunbeams. This angle defines the heating power of sunlight. If you flash a flat surface with a torch in steep angle, you can see that light focuses in one spot, but if you slant the torch, the same light spreads on a larger area and its power is weaker. The same thing happens with sunlight. Winter is cold, because the heating power of sunbeams is less. You can feel this every day, because at dawn and at dusk the weather is cooler than at noon. While we are freezing on the northern hemisphere, summer begins on the southern. Our Australian friends put on swimsuits, while we stand against chill wind in hat and gloves. Whether it snows, rains or sleets depends on the temperature. Even one air mass – for example a winter storm – could have different parts regarding temperature. On the warm side of the storm, a shower can develop; there is sleet on the borderline of cold and warm parts, while you can see snowfall on the cold side.

What makes snowflakes in a cloud and in a snow machine?

As they are smaller than the diameter of a hair, you can observe different special forms of snow-crystals with naked eye only if your eyesight is sharp enough. If it is not, you can use a microscope or a microscope objective with a camera. In 2013, physics professor Kenneth Libbrecht made a snow machine (dual diffusion chamber), in which you can grow snow-crystals, and snow-crystal development can be observed in clouds created in the chamber. The process starts with water vapour precipitation and tiny vapour drops are created in the air, some of which freeze and these ice-crystals form the cores of later snowflakes. Vapour precipitates in frozen form on the surfaces of snowflakes thus, their size grows by thin layers.

Why do not two identical snowflakes exist and what do you need for a beautiful snowflake?

Each snowflake has six almost symmetrical branches. Its form is defined by the method how water molecules are connected to one another inside it. When water freezes, atoms arrange in a crystal lattice that can create only hexagonal structures. (Except for ice VII, but it is very rare on the Earth.) The symmetrical hexagonal structure causes that snowflakes are also symmetrical. The pattern is developed in a cloud and it is formed further into slim needles, thick columns, flat plates, twiggy stars and many other ways depending on the weather.

Two identical snowflakes cannot be developed, because changing humidity and temperature during their ways in the cloud have important roles in the created shapes. Identical snowflakes should make exactly the same way, with the same airflows, temperature and humidity. Thus, it has a rather little chance. Lower humidity in a cloud results in simpler forms, while higher humidity makes more complex forms. If you decide on taking photos of snowflakes, it is important where to do it, because not every place is ideal to develop really nice snowflakes. The best conditions are high but fluctuating humidity, minus 15 °C degrees and no wind, because wind damages them.

Why is ice slippery?

At the beginning of the 2000s in the University of California Berkeley, Hungarian-born chemist professor Gábor Somorjai discovered that ice is covered with a kind of fluidic layer. Molecules in fluid water can move freely in all directions, while in frozen water, they connect to one another closely, but the molecules on the surface do not have anything to connect to. This is the reason why they can move freely and form a thin slippery layer on the surface of ice.

Minus 89°C and the tower-tall snowman

In the mountain village of Bethel (USA) in February 1999, several dozens of volunteers and a crane built a record-large 35-metre-high snowman during 14 days, by using 5600 cubic metre of snow. The giant snowman survived the whole winter and melted completely only in June. The colder it is, the longer your snowman lives! The recorded lowest official temperature on planet Earth was -89.2°C recorded at the Russian Vostok Station on the South Pole in the winter of 1983. They needed a special thermometer to measure it, because mercury freezes at -38°C degrees. Thus, they used a thermometer filled with alcohol because its freezing point is lower.

The coldest village on the Earth 

Villagers of Oymyakon are convinced that they live on the coldest place of the Earth. Although it is not the coldest place, it is the coldest permanently inhabited settlement indeed. The village is situated in northeast Siberia by the River Indigirka. The average winter temperature in Oymyakon is around minus 60°C degrees, and the coldest temperature record was – 67.7°C measured in February 1933. If you want to move there, you have to prepare for hard winters! Cars are regarded as luxury, because they have to warm the engine 24 hours a day, otherwise – if they are stopped – they will not restart. If you lived there, you would not need a fridge or a freezer in winter, because frost never melts during the cold season. Milk is not sold by the litre, but in frozen blocks measured in centimetres. Schools are closed only if the temperature falls lower than minus 52°C degrees (but some sources say they do not even then). There is only 12 °C in school classrooms, but local people think that cold can be tolerated and they comply with it by living in well-insulated houses for example. Many people live longer than a hundred years, which might be due to the fact that they eat a lot of raw meat and fish (according to certain theories), besides the beneficial effect of cold (see cryotherapy).

Károly Erdélyi

Translated by Zita Aknai

References

• Gyula Gábris, Miklós Marik: Csillagászati földrajz (2011). (in Hungarian)
• Ward Cameron: What Causes Winter? mountainnature.com (2005).
• Kimm Fesenmaier: Snowflake Science - Caltech Physicist Explains Why Snowflakes Are So Thin and Flat, California Institute of Technology, caltech.edu (2011).
• Joseph Stromberg: The Art and Science of Growing Snowflakes in a Lab: Physicist Kenneth Libbrecht can make snowflakes with elegant spindles or blocky tabs by manipulating temperature and humidity, smithsonianmag.com, 5 December 2013.
• Lisa M. Krieger: Meet the Caltech professor who’s building a bigger snowflake, The Mercury News, mercurynews.com, 25 December 2017.
• Slippery All the Time, The Science of Hockey, exploratorium.edu.
• Gabor A. Somorjai (2002). The Evolution of Surface Chemistry. A Personal View of Building the Future on Past and Present Accomplishments, The Journal of Physical Chemistry. B,  106 (36), p. 9201–9213. 
• Yimin Li,  Gabor A. Somorjai (2007). Surface Premelting of Ice, The Journal of Physical Chemistry C,  111 (27), p. 9631–9637.
• Bethel Area Chamber of Commerce: Bethel's World Record Snowpeople (2018).
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