What shapes do snowflakes come in? Why is snow not cold chemically cold? Is there a scientific basis for the saying "snow is an omen of a good year"?

1. Snowflakes come in many shapes and are very beautiful. If the snowflakes under a magnifying glass, you can find that each snowflake is an extremely fine pattern, even many artists have been marveled at. But how are the various snowflake shapes formed? Snowflakes are mostly hexagonal, which is because snowflakes belong to the hexagonal crystal system. Snowflakes in the clouds "embryo" of small ice crystals, there are two main shapes. A hexagonal, long and thin, called column crystal, but sometimes it is pointed at both ends, like a needle, called needle crystal. The other is in the form of hexagonal flakes, like the slices cut from a six-pronged pencil, called flake crystals.

If the surrounding air is less supersaturated, the ice crystal grows slowly and evenly on all sides. It remains as it is when it increases and falls, and is called columnar, needle, and flake snow crystals, respectively.

If the surrounding air is highly supersaturated, the ice crystals not only increase in size as they grow, but also change shape. The most common is a change from flakes to stars.

It turns out that as ice crystals grow, the water vapor near them is depleted. So the closer you get to the ice crystal, the thinner and less supersaturated the water vapor is. In the area immediately above the surface of the ice crystal, saturation is just reached because all the excess water vapor has condensed on the ice crystal. Thus, the density of water vapor close to the ice crystal is going to be less than farther away from it. Water vapor moves from around the ice crystal to where the ice crystal is located. The water vapor molecules first encounter the corners and projections of the ice crystal, where they condense and cause the ice crystal to grow. The corners and projections of the ice crystal will first grow rapidly and gradually become branched. Later, for the same reason, new twigs and forks will grow at the angles and corners of the ice crystals. At the same time, in the depressions between the angles and forks. The air is no longer saturated. Sometimes there is even a sublimation process here, so that water vapor is transported elsewhere. This makes the corners and forks more prominent, and slowly the familiar star-shaped snowflakes form.

The above is actually a typical process of formation of a star-shaped snowflake. Its equivalent parts, regardless of shape or size, should be identical. This typical star-shaped snowflake can only be formed in an ideal, calm environment (e.g. in a laboratory). In the atmosphere, it cannot increase in steps as described above, and the resulting shape is not as typical. This is due to the fact that the ice crystals are gradually falling and sometimes rotating, and the amount of water vapor to which the branches are exposed varies from branch to branch, and those branches which are exposed to more water vapor grow more. Therefore, the snowflakes we usually see are largely the same but different from each other.

In addition, the snowflake in the cloud in the process of descending, but also from the environment suitable for the formation of the shape of the environment down to the formation of another shape of the environment, and so it will be out of the view of a variety of complex snowflake shape. Some are like cufflinks and some are like spikes. Even if they are all star-shaped snowflakes, there are three branches of the fork, six branches of the fork, and even twelve branches of the fork, eighteen branches of the again.

The above are all cases of individual snowflakes. As the snowflakes descend, the individual snowflakes can also easily climb and merge with each other to become larger snowflakes. The merging of snowflakes is mostly observed in the following three situations. (1) When the temperature is below 0°C, snowflakes collide on their way down slowly. The collision generates pressure and heat, which causes some of the colliding parts to melt and stick to each other, and then this melted water freezes again immediately. In this way, the two snowflakes merge together. (2) at a temperature slightly above 0 ℃, snowflakes have been covered with a layer of water film, then if the two snowflakes touch each other, it will take advantage of the surface tension of the water and stained together. (3) If the branches of the snowflake is very complex, the two snowflakes can also be simply because of the simple climbing and hanging together.

Snowflakes travel a long way from the clouds to the ground, and when conditions are right, they can become very large by climbing together many times. In the case of heavy snowfall, there are sometimes goose feather-like flakes that have been merged many times.

But sometimes when snowflakes touch each other, they don't merge with each other, but are broken, which produces some deformed snowflakes. For example, in the snowfall, sometimes see some single "star branch", belong to this situation.

2. When it snows, the snow falls from the sky, and generally does not absorb the heat in the air. So it does not feel very cold, but wait until the snow melts. Snow from solid to liquid need to absorb a lot of heat from the air, is the surface of the ground temperature is lowered, it will feel cold. So there is a "snow is not cold, snow cold."

There is another saying

Melting snow is colder than snow

The current junior high school physics textbook asks in the section "Melting and Solidification" "Why is it cold to melt snow when it's not cold to snow?" According to the teacher's guide and the "100,000 reasons - weather" volume of the explanation, to the effect that: snow and water ice, to exothermic; and melting snow ice melt into water, to absorb heat. Therefore, the snow is not cold melting snow cold.

In fact, this explanation is wrong!

Nice, water icing to exothermic, and ice melting into water to absorb heat, but according to the basic laws of thermodynamics: the object's heat can only be transferred from the high temperature object to the low temperature object. Mutual conversion temperature of water and snow and ice is 0oC, water icing exothermic to the environment will make the ambient temperature rise, but the maximum is not likely to exceed 0oC, otherwise the flow of heat will "turn around"; on the other hand, the snow melts into water to absorb heat, so that the ambient temperature drops. But the lowest ambient temperature can not fall to below 0oC, or below 0oC environment will make the process of melting snow and ice "reversal". Therefore, theoretically, snow can never be lower than the melting temperature.

So what is the relationship between snow or snowmelt and ambient temperature in practice? On the one hand, snow and ice and water conversion of the physical law remains unchanged, but on the other hand, due to the morning and midday temperatures in the day, different places at the same time (such as sunny and backlit place) the temperature is not the same, coupled with the white snow and dirty snow heat absorption capacity is different, and even if the ambient temperature is higher than 0oC, the snow melting there is also a process, as well as the impact of the wind speed and humidity, so that the person feels the cold and heat and the physical The temperature is not exactly the same. This makes the problem of "snow not cold snow cold" greatly complicated.

To scientifically determine the "snow is not cold snow cold", first of all, we must figure out what is called snow, what is called melting snow, for example: the first snowfall each year, because the snowflakes are formed in the high altitude, in the high altitude air temperature is far lower than 0oC, but this time the ground temperature is often in the 0oC above. Thus, the snow melts as soon as it hits the ground. Although in the snow but the snow melts as it falls, the temperature is always above 0oC, this situation is counted as snow or snow melt? Moreover, this kind of snow melting in Jiangnan is very common, if this situation is only categorized as a snow day, then it will be very natural to come up with "snow is not cold snow cold".

But from a strict sense, this side of the snow melting weather, should not be categorized only to the category of snow days. In order to facilitate the statistical summarization of meteorological data, can this snow day and melting snow day to define: "Where the next day there is snow, although the first day under the snow when the maximum temperature in the 0oC or more, or as a snow day. And there is snow without snowfall, the maximum temperature above 0oC weather are regarded as snowmelt days." In accordance with this standard, the author spent more than 100 yuan to transcribe the entire snowfall process in Nanchang in the past decade of meteorological information. Although the statistical judgment based on this information is still insufficient, but I really do not have the financial resources to buy more information.

Now from the Nanchang City in the last ten years of snowfall process statistics, the average maximum temperature of the snow day is 1.5oC, the average minimum temperature of -2.76oC, the average snow day temperature is -0.63oC. And the average maximum temperature of the snow day is 3.2oC, the average minimum temperature is -1.8oC, the average daily temperature of the snow day 0.7oC. Visible in general, the snow day than the chemical Snow day temperature is lower. Therefore, the so-called "snow is not cold, snow cold" in physics is not valid.

Since the temperature on a snowy day is lower than on a snowy day, why is it said that "snow is not cold, but snow is cold"? In addition to the beginning of this article has denied the explanation, the author has also collected the following explanations: 1, dry thermal insulation said; 2, snow wind said; 3, radiation heat said; 4, overkill said. Below we analyze these several explanations one by one.

A, dry insulation said: this view that the snow when the air humidity is low, relatively dry, so that the air and clothing warmth is relatively good, and snow days air humidity is relatively large, air heat transfer is strong, so that people feel cold.

In this regard, we say: snow when the snowflakes flying all over the sky, snow and water everywhere, the two weather, the relative temperature is very large, and 0oC when the saturation vapor pressure of ice and water saturation vapor pressure is the same, so the relative humidity of the snow day with the snow day should not be much difference. From the meteorological statistics of Nanchang area: the average relative temperature on snowy days is 81.8%, and the absolute humidity is 4.8 mmHg. While the average relative humidity on snowing days is 83.6%, the absolute humidity is 5.38 mmHg. Although the humidity is slightly higher during melting snow, the effect on the air heat transfer coefficient is almost zero. As for the warmth of clothing there should also be very little difference. Therefore, this small change in humidity will not produce a significant "snow is not cold snow cold" effect. The above argument, while valid, is not well founded.

Two, the snow wind said: "snow often windy, so it seems very cold". According to Nanchang in recent years, the weather statistics, snow day average wind speed of 2.3 m / s, the snow day average wind speed of 1.1 m / s. Therefore, this theory is not enough.

Three, amplitude heat dissipation said: "snow day generally to the sun, the air without support, so that the night ground heat is easy to dissipate, so the minimum temperature of the snow day is lower than the snow day." According to Nanchang area statistics: snow day average temperature of -2.76oC, snow day average temperature of -1.8oC. minimum temperature or snow day low, so this theory is not established.

Four, overkill said: "snow is not cold snow cold, mainly for the ancients to emphasize the snow day is still very cold a kind of overkill, in fact, or snow than the snow cold. Similar to this overkill statement, there are many weather proverbs in China, such as: "after the fall there are eighteen autumn tigers more powerful." This is to emphasize that the weather is still very hot after the beginning of autumn. The above statement has a certain truth, here can be said to check.

Looking at the above various explanations are not quite understandable. In this regard, the author according to the results of the survey in rural areas to put forward the following new interpretations, with everyone to discuss.

First of all, the person who can conclude that "snow is not cold, snow is cold" is definitely the lower intellectuals and laborers. Because those dignitaries, in and out of the sedan chair and fur coat, at home with a brocade tent fire pit, at any time someone waiting to add or subtract clothes, generally rarely feel cold. According to the traditional education of Confucianism, they should only be concerned about cultivation, Qi, governance, and peace. Those "unworthy sons" of Confucianism think about the wind, flowers, snow, and moon, and snuggle up with Cuiwei and Hong, and therefore do not care about the cold and warmth of snowy days and snowy days. The middle and lower intellectuals and laborers, live in a hut, out to rely on their own walk, which allows them to appreciate the "snow is not cold snow cold".

According to the author's survey, until the forties and fifties of this century, farmers living in rural areas near Nanchang are basically straw houses. Straw is wet, it is easy to rot, and not heat preservation, so farmers living in straw houses, after the fall harvest, the original house to cover the straw into the year's hay. So far, although the farmers live on the tiled house, but also retained the habit of the year, every year before the winter on the cattle pen grass should be completely changed once. Asked the reason, the answer is: "winter does not change grass, cattle will freeze disease and death." Because our country is a monsoon climate, winter is generally cold and less rain. So the grass replaced before and after the winter, before the first snowfall, will generally remain dry. Especially in the yellow and huaihuai valley winter rarely rains, even in the snowfall before the rain after a period of sun and wind should also be relatively dry. So when the snow thatched roof should be relatively dry. But in the snow, due to the daily temperature difference, it is not possible to melt all the snow on the roof on the same day, because of the snow water **** storage, so that the snow water accumulates in the roof, so that the water has sufficient time to seep into the thatch. Because thatch insulation is mainly rely on the grass wrapped in the immobile air, once these air is filled with water, is bound to make the roof insulation greatly reduced. According to the test, the thermal conductivity of water is 60 times the air, although the average temperature when it snows to be lower than the snow 1 --- 2oC, but as long as the thatch humidity increased by 10% will be enough to make people feel the snow indoor temperature is lower.

There is still a lot of heat generated indoors due to human activities such as cooking. Together with the doors and windows closed more tightly (Kotian to paste the windowpaper) heat is not easy to dissipate, even if the outside cold to minus ten degrees, due to the snow itself a good thermal insulation can make thatch and contact with the interface, the temperature in -1oC or so. And because of the thick thatch is wet with snow, a lot of heat leakage, thus making the outdoor temperature close to the outdoor temperature results in indoor temperature than the aforementioned snowy low, natural indoor people will feel "snow is not cold snow cold".

For those who go out. Although rubber has been used in foreign countries for hundreds of years, but China's rubber rain shoes "fly into the common people's home", or the forties and fifties of this century. According to the author's survey, before the forties, the upper class wear leather shoes in winter, middle-income wear cotton shoes, the general public wear cloth shoes, hemp shoes, straw shoes. Rainy and snowy days can add another pair of clogs, even if it is very good. And these shoes of a **** the same point is not waterproof. It does not matter to the dignitaries, anyway, in and out of the sedan chair riding a horse, but for the middle and lower classes, the snow day had to be not waterproof shoes on the snow, the result of the snow soaked shoes and socks, so that the feet of the cold close to 0oC. And the snow day, although the temperature is even lower, but because there is no melting point of the ice. Snow is "dry", not wet shoes. The warmth of the shoes is good, but the temperature of the feet is much higher than when the snow is melting and the shoes and socks are stepped in the snow water. This is something I believe we can all relate to. As the saying goes, cold starts from the feet, and cold feet will not only make a person feel cold all over, but also make him/her prone to get sick as a result. This amplifies the impression that the chemical snow is cold even more.

To summarize: Until not so long ago, the average person felt colder subjectively on snowy days because of the roofing materials of the average person and the lack of waterproofing of shoes and socks, whether they were outside or at home. Therefore, in the past, the proposition that "it's not cold when it snows, it's cold when it snows" was valid. However, this does not mean that the temperature on a snowy day is higher than on a snowy day. The traditional explanation that "snow excretes heat and snow absorbs heat" is wrong.

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3. The solution to the problem of snowy year

Legend has it that snow on earth is controlled by three immortals in the sky, namely, Zhou Qiongji is in charge of Hibiscus City and Dong Shuangcheng is in charge of the snow storage glass bottle, which contains several pieces of snow. Whenever the tongyun clouds are dense, Gushu Zhenzhen knocked out a piece of snow with a golden tendon, and snow started to fall on the earth. The Creator gave the snowflakes to the winter, so that the winter in the bleak in the life, silence added fun. Farmers love the snow, once they see the snow flying in the sky, the ground piled up thick fluffy snow, the joy of the coming year's harvest is foretold. "Rui Xue Zhao Feng Nian", in fact, is the people from the heart of the snow praise. "The reason for this is that the snow layer protects the winter crops from freezing and keeps them warm. Newly fallen to the ground snow is loose and porous, which can contain 40% -50% of the air. Because the air is not easy to heat transfer, so the earth is like a large and soft quilt cover. This "quilt" can prevent the heat in the soil to the outside, but also to prevent the invasion of cold air. Measurements show that the ground snow thickness of 20 centimeters, the surface temperature of the snow than the surface temperature under the snow to be as much as 15 ℃ lower. When the snow thickness of 30 centimeters, even if the temperature is reduced to minus 30 degrees Celsius, wheat will not suffer frost damage. "The snowy season is a good year because it increases the moisture content and fertilizes the field. Snow on the ground melts slowly when the ground warms up in the spring of the following year. Melted snow water loss is small, most of the seepage into the soil, like an irrigation, to alleviate the spring drought, good spring planting is very good. Melted snow water, can bring more nitrogen compounds to the soil. According to measurements, a liter of rain containing nitrogen compounds 1.5 grams, and a liter of snow water containing nitrogen compounds can be up to 7.5 grams more, it is clear that the snow will increase the fertility of the soil. In addition, due to the snow was covered, the soil freezing depth is shallow, leaves, grass roots, etc. can continue to rot into fertilizer. "RuiXueZhouFengYi" lies in the insecticidal effect of snow. Ming Dynasty Li Shizhen "Compendium of Materia Medica" said: "snow, wash also, wash away the itching plague insects and locusts also. Three snow before the wax, the big suitable vegetables and wheat, and kill insects and locusts." Winter snow can freeze locusts, borers and other overwintering pests eggs. The earlier the snow falls, the stronger the killing power. "Rui Xue Zhao Feng Nian" also lies in the fact that snow water has a significant effect on increasing production. Ming Dynasty Li Shizhen's "Compendium of Materia Medica" said: "with (snow) water soaked grains, then drought-resistant insects." For example, rice seeds after snow water immersion, catalyze the rice seedlings root buds thick, inserted in the field, tillers are also more, compared with the use of well water soaking seeds, an increase in yield of about 20%. Cucumber seeds soaked in snow water, germination rate is 40% higher than ordinary water soaked. In the cucumber growing season with snow watering, yield can increase by 21%. Cotton seeds soaked in snow water can increase yields 1 into 2 into. Xinjiang desert and Tibet plateau in some places to grow fruits and vegetables, the reason why the growth of fat and strong, and there irrigation water from the Tianshan Mountain and the Kunlun Mountains of the melting snow has a certain relationship. Tests also show that three months of piglets, drinking snow water than drinking ordinary water, weight can be increased by 2 / 3. Snow water fed to hens, than drinking ordinary water hens, their egg production has also increased significantly. Snow has such a peculiar function is determined by its own nature. First, the newly fallen snow is loose and porous, can store a lot of air, have anti-freezing and warming effect. Secondly, after melting the snow water in the heavy water content than ordinary water 25% less. Heavy water is a kind of radioactive material, which has a strong inhibitory effect on the life activities of various organisms. The low content of heavy water in snow is obviously conducive to the promotion of biological growth and development. Third, the physical and chemical properties of snow water and general water is also different. Snow water as a result of freezing, excluding the gas, conductive properties and density changes. Studies have shown that snow water in terms of its physiological properties, and biological cells within the nature of water is very close, therefore, showing strong biological activity. The ability of plants to absorb snow water is two to six times greater than the ability to absorb tap water. When snow water enters the organism, it stimulates enzyme activity and promotes metabolism. Fourth, snow water contains more nitrogen compounds, five times more than those in rainwater and higher than ordinary water, which can be said to be a kind of fertilizer water. "Falling red is not an unfeeling thing, turning into spring mud protects the flowers even more." This is how the snow with its "life" fertilizes the land, nourishes the crops, for the benefit of mankind.

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