Seven cold knowledge about snow

1, snowflakes are hexagonal?

Snowflake is a beautiful crystal, also known as Weiyanghua and Liuchu. It is a snow crystal polymer formed by contacting, bonding and hooking snow crystals together. At present, there are about 20 thousand known snowflake shapes, which can be said to be varied and colorful.

The original "embryo" of snowflakes-snow crystals are basically hexagonal in shape, such as hexagonal branches and hexagonal sheets, and the snowflakes grown from them also show hexagonal characteristics. Therefore, the ancients said that "there are five flowers in the vegetation and six snowflakes alone".

The basic shape of snowflake is hexagonal, but it can show various shapes in different environments. There are hardly two identical snowflakes in nature, just as there are no two identical people on earth.

This is mainly because the temperature and humidity in the snow cloud change rapidly during the growth of snowflakes, and the shape of snowflakes will be different as long as there is a slight difference.

2. Can it "snow" when the sun is shining?

There is such a lyric in Nanshan South: "You are in the south where the sun is shining and the snow is falling", which seems illogical at first glance. However, this phenomenon did happen, and more than once. This phenomenon is called "solar snow".

It snows when the sun is shining, so it is called "solar snow". This phenomenon is common in the north of China and rare in the south, but it is a normal weather phenomenon.

Usually, "solar snow" is a kind of short-term snowfall, which usually occurs around 9- 10 in the morning or around 15- 16 in the afternoon. During these periods, when the clouds that produce snowfall are not thick and the coverage is not large, there may be sunlight coming out obliquely from the cracks in the clouds, so you will see the scene that sunlight and snow appear on the ground at the same time.

"Solar snow" is somewhat similar to "solar rain" in summer, except that the temperature of the clouds that produce "solar snow" is low, and the precipitation falls in the form of snow.

3. "Snow particles" are not snow?

Maybe everyone has seen this phenomenon: sometimes white "balls" will fall from the sky and fall to the ground. Many places call it "snow grains" or "rice snow". In meteorology, this kind of thing is called graupel, also known as snowball or soft hail. Its diameter is generally between 0.3 and 2.5 mm, and it is brittle and fragile.

But you should know that although graupel and snow are both solid precipitation, they do not belong to the category of snow. The graupel usually lands when the ground temperature is not too cold, and usually lands before it snows, which can be said to be a "prelude" to snow. It is produced in a cloud with strong disturbance, and it is formed by a large number of snow crystals (or snow masses) colliding with Leng Yun drops and freezing, often in an array.

4. How big is the snow?

We often use "lightness" and "goose feather" to describe snowflakes, which shows their lightness. Snowflakes can only be weighed on an extremely accurate analytical balance. About 3000~ 10000 snowflakes add up to one gram. However, it can collapse houses and gas stations!

Mainly because when they are together, they can gather sand into a tower and win by quantity. According to statistics, the number of snowflakes in a cubic meter of new snow can reach 8 billion!

To make it easier to understand, let's first estimate the weight of snow from the perspective of precipitation. Under normal circumstances, in the northern area of 1 m2, the snowfall thickness of 8 8~ 10/0mm melts into water, which is equivalent to the precipitation of 1 mm; In the south, the snowfall with a thickness of 6-8 mm on the area of 1 square meter melts into water, which is equivalent to the precipitation of 1 mm.

According to the density of water, we can easily draw a conclusion that in the north, the snow weight of 8 ~ 10 mm is about 1 kg, then the snow weight of 8~ 100 mm 100 kg. In the south, the snow weight of 6~8 mm in the area of 100 square meter is 100 kg. It can be seen that the snow with the same thickness is heavier in the south than in the north.

More specifically, a flat roof of 100 square meters, if the snow reaches the knee, will bear the weight of 3-5 tons or more, which is equivalent to more than 20 fat people standing on the roof with a weight of about 200 kilograms. Its weight can be imagined!

5. Can snowflakes be as big as seats?

"Yanshan snowflakes are as big as seats, and pieces fall on Xuanyuantai." This is a poem by Li Bai, a great poet in the Tang Dynasty. Can snowflakes really be as big as seats? In fact, don't say that there is no record in the history of snowflake science, and even "goose feather snow" is not easy to encounter.

According to the official website of Guinness World Records, the largest snowflake reported so far was found in Fort Keogh, Montana, USA on128/00. He measured that the snowflake was 38 cm wide and 4 mm thick, "bigger than a milk pot".

The New York Times said that "there is no conclusive evidence to support this statement", and now Guinness official website can't find this record.

In fact, the diameter of a single snowflake we can see is generally between 0.5 and 3.0 mm, and the maximum diameter will not exceed 10 mm, at most it is as big as our nails. Those seemingly large snowflakes, such as the so-called "goose feather snow", are actually not a snowflake, but are formed by many snowflakes sticking together.

When the air is humid, the merging ability of snowflakes is particularly great, and many snowflakes merge into one piece. Therefore, strictly speaking, goose feather snow can't be called snowflake, it is just the aggregation of many snowflakes.

6. Do snowflakes have "cores"?

To form snowflakes, there are two conditions: one is that water vapor is saturated, and the other is that there must be condensation nuclei in the air. Some people have done experiments, if there is no condensation nucleus, the water vapor in the air will be supersaturated to the degree of relative humidity above 500%, and it will condense into water droplets.

But such a large supersaturation phenomenon will not exist in the natural atmosphere. So without condensation nuclei, it is difficult for us to see rain and snow on the earth.

Nucleation is a particle that plays a role in the process of changing a substance from gas to liquid or solid, or from liquid to solid. In the process of forming precipitation, the ideal condensation nuclei are those particles that absorb the most water, such as sea salt, sulfuric acid, nitrogen and other chemicals.

So the snowflake we see is actually a "core".

7. Who was the first person to take pictures of snowflakes?

Wilson Bentley is an ordinary man, 1865 was born on a farm in Vermont, USA. He has been interested in observing nature since he was a child, especially fascinated by snowflakes. Before 19 years old, he began to record his deep love for snowflakes and became the first person to shoot snowflakes in history.

He also devoted his life to snowflake with "the strong love of his lover and the unparalleled patience of scientists". He photographed more than 5,000 snowflakes in his life, and the shapes were not repeated. He can be said to be a well-deserved "Snowflake Man".

Bentley's micrographs of snowflakes appeared in scientific journals, and only Nature published 60 photos. These photos have influenced many scientists, photographers and museums. "Snowflake Man" also became a scientist and wrote the book Snow Crystal.