The wind is cold and the first snow is drifting. The arrival of the light snow festival means that the cold tide is frequent and the winter is gradually flourishing.
At this time, the temperature in many places continued to decline, the minimum temperature in the northern region was mostly below zero, and the precipitation state changed from rain to snow, and north China, Huanghuai and other places ushered in the first snow of winter.
Because it is about to enter a period of food scarcity, the custom of the snow festival is mostly related to eating. Just like birds, squirrels and other animals have to store food for winter, humans have similar behaviors, such as pickles. Some places in the south have the custom of eating rice dumplings in the tenth month of the lunar calendar. Fishermen in the south-central coast of Taiwan dry fish and store dry food before and after light snowfall.
As the weather gets colder and colder, before and after the light snow, the ancients will prepare some heating equipment, such as copper hand stoves, soup mothers, and rich families will also use a metal hand warmer sachet.
In the face of an active cold snap, farmers everywhere are busy harvesting, cold protection, and field management. They also look forward to snowflakes falling from the sky. "The snow is full of snow, and the coming year will be a good year." Light snowfall is conducive to enhancing soil fertility, reducing pests and diseases, and also means that the rainfall is uniform in the coming year, and there is no obvious drought and flood.
The light snow festival in 2021 will cover three phenology: "rainbow is not seen", "weather rises, earth gas declines" and "occlusion becomes winter".
<b>A little snow: The rainbow is gone</b>
On the first five days of light snow, the rainbow was gone.
In the cold winter, the color of the sky is also a little monotonous. When it snows, the sky and the earth are white. The snow stopped, the sky was often gray, and the brilliant rainbow almost never appeared in the winter sky.
The appearance of rainbows requires the reflection and refraction of water droplets, plus clean and fresh air. After entering the winter, the air is relatively dry, and because of the low temperature, the moisture in the air is often in the state of ice crystals, and the refraction of sunlight is different from that of water droplets; in the places where there is no snow in the south, because of the change in air pressure, multi-layered clouds in winter, often cloudy after rain, covering the sky, coupled with the winter air haze, the beautiful rainbow is invisible.
Despite the lack of the brilliance of the rainbow, the white snow makes winter feel a little more pure.
Snow is precipitation in a solid form composed of a large number of white opaque ice crystals (snow crystals) and their polymers (snow masses). As part of the water cycle, snow was formerly a cloud in the air. Cotton-like clouds are composed of small water droplets and Xiaoice crystals, including water clouds dominated by small water droplets, ice clouds dominated by Xiaoice crystals, and mixed clouds composed of small water droplets and Xiaoice crystals.
The source of snow is mainly mixed clouds. When the temperature drops, the water vapor in the air reaches saturation, and the excess water vapor is adsorbed by ice crystals under the action of the condensation nucleus. Ice crystals continue to grow, sometimes Xiaoice collide with each other and form large ice crystals, until the weight of the ice crystals exceeds the air resistance and buoyancy, and suddenly falls, it becomes snow.
Snowflakes grow on the basis of ice crystals, so, similar to ice crystals, snowflakes are often hexagonal. As early as the Western Han Dynasty, the ancient Chinese discovered the unique structure of snowflakes and solemnly recorded: "Where there are five more flowers of grass and trees, six snowflakes alone."
In fact, compared to the 19 forms of ice crystals that have been discovered, snowflakes are no less diverse. Wilson Bentley, a farmer from a remote farm in Vermont, USA, was the first person in the world to photograph snowflakes. Fascinated by snowflakes since childhood, he bought his first camera at the age of 19 and creatively assembled it with the microscope he usually uses to observe snowflakes, so he had a homemade macro camera. In the winter of 1885, the first ever photograph of a snowflake crystal was born.
In his lifetime, Bentley photographed more than 5,000 snowflakes without any repetition of shapes.
Scientists have been trying to deduce the physical formula for snowflake shape formation for years, and yet the exact variable factors have not yet been studied. Andy Brenning, a chemistry teacher in Bournemouth, England, has created an infographic based on the latest research showing a classification of 35 snowflake shapes, which researchers at Kitami Institute of Technology in Hokkaido, Japan, further divided into 121 categories.
Ice crystals as snowflake "embryos" come in three main shapes: thin and long hexagonal prismatic crystal columns, needle-like needles with two pointed ends, and thin hexagonal wafers.
The results show that the shape of the snowflakes that eventually form is directly related to the temperature and humidity in the clouds. In general, when the humidity is high, the snowflakes are generated faster and the shape is more complex, such as delicate stars or dendritic; when the humidity is low, the snowflakes are slow to form, and it is easy to form simple flakes or powdery snowflakes.
Clouds of different temperatures will not only breed snowflakes of different shapes, but also affect the "body shape" of snowflakes: six-petaled star-shaped snowflakes are only formed when the cloud temperature is about -15 ° C, clouds at about -6 ° C will form needle-shaped and columnar snowflakes, at 0 ° C, snowflakes are generally horizontally expanding regular hexagons, with no gaps between the apex corners... When the temperature is extremely low, the crystals of snowflakes will be so small that they are almost invisible, and as the temperature rises, the closer they are to 0 ° C, the larger the crystals of the snowflakes will become.
As the snow drifts from several kilometers of clouds to the ground, the snowflakes are also affected by the direction of the air flow and change more. Snowflakes weigh extremely lightly, from five thousand to ten thousand snowflakes weigh about a gram. Snowflakes of all sizes stick when they meet in the air, especially when temperatures are relatively high. When many snowflakes are joined together and merged into snow balls with a diameter of several centimeters, they become the "goose feather snow" in people's eyes, sometimes in an irregular shape, sometimes in the shape of an unequal number of branches and stars.
For centuries, the mystery of snowflake formation has plagued scientists and pushed them to continue to study and experiment. The shape of snowflakes is determined by the scientific laws of crystal growth, telling everything they go through during their formation. Its complex symmetry stems from the crystal's miraculous ability to assemble itself—crystals, plants, animals, and even humans are made up of self-assembled parts under certain laws.
This creature of nature carries a variety of messages thousands of meters in the air, floating down to the mortal world, becoming the protector of crops, the purifier of the air, and the source of inspiration for literati and inkers. That fleeting beauty contains the deepest mysteries of nature, leading to the mystery of the formation of everything in the universe.
<b>Light snow weather: the weather rises, the earth's gas falls</b>
On the second five days of light snow, the yang in the sky rises, the yin in the ground falls, and the yin and yang do not intersect.
This is perhaps the most difficult and mysterious of the 72 phenology. In the interpretation of different generations in the past, "weather" and "earth qi" are usually interpreted as yang and yin. In the traditional concept of the ancients, "weather" is yang qi, "earth qi" is yin qi, and when the snow is seasoned, the yang qi rises and the yin qi falls, resulting in the impassability of heaven and earth, the yin and yang are not intercourse, and all things lose their vitality.
From a scientific point of view, what exactly do yin and yang mean? Are they just things imagined by the ancients?
If "yin qi" and "yang qi" are understood as air flow, "yin qi" is the sinking air flow close to the ground, and "yang qi" is the air flow rising in the air. What is the phenomenon that the two streams of air are irrelevant to each other and move in reverse?
The atmospheric "coat" that envelops the Earth's surface can be divided into tropospheres, stratospheres, mesospheres, thermal layers and diffuse layers according to their height. The closest thing to the surface is the troposphere, where weather phenomena such as rain, snow, and hail occur. In general, the temperature in the troposphere decreases with the increase of altitude, so the air near the ground is high, the density is small, and the air pressure is low, while the air temperature in the upper layers is low, the density is large, and the air pressure is high. This "top-heavy" air pressure distribution makes it easy for the air to tumble up and down, forming convection.
However, when cold air invades in winter, the temperature of the near-stratigraphic air will drop very low, and the upper atmosphere will cool less, and there may be an anomaly of warming and cooling, which is called inversion in meteorology.
When the phenomenon of inversion occurs, the air is "light-headed" and in a stable state. The cold air near the ground continues to sink, and the relatively warm air in the air continues to rise, which is the origin of "the weather rises, the earth's air falls". The inversion layer is like a thick quilt covering the sky, and the air in the upper and lower layers is no longer flowing and exchanging, often resulting in weaker or even no wind. If the relative humidity of the air is high, it will promote the formation of clouds, fog, and smoke, so that the visibility of the air in the inversion layer is reduced, so we see the foggy sky.
If it rains at this time, it is generally stable precipitation, such as continuous light rain or drizzle.
Sometimes, however, temperature inversion can also be a favorable factor for the occurrence of strong thunderstorms. At this time, there is usually stable cold air near the ground, and the middle and low layers have strong warm and humid air to form an inversion layer, which blocks the vertical exchange of heat and water vapor and accumulates unstable energy. Although the air near the ground is difficult to penetrate the inversion layer, the air inside the inversion layer becomes warmer and wetter, and once the impact forces destroy the inversion layer, the air is lifted upwards, which will produce strong convection. This is the reason for the appearance of winter thunder, commonly known as "winter thunder" or "thunder and snow".
<b>Three seasons of light snow: closed to winter</b>
On the third five days of light snow, the heating and cold air no longer circulated with each other, and the heavens and the earth were closed and turned into a cold winter.
The "occlusion" in the three seasons of small snow has two meanings, one refers to the occlusion of heaven and earth caused by the incompatibility between "weather" and "earth gas"; the other refers to the scene where animals hibernate in the ice and snow environment, traffic is not smooth, and people can't leave their homes.
Nowadays, under the "blessing" of science and technology and economic development, people can still move freely even in the coldest season, have heating in their homes, and have down jackets when they go out, and the meaning of "blocking" in winter has faded a lot.
However, the inversion phenomenon caused by the reverse movement of cold and warm currents still has a strong influence in today's society, and even plays a more important role due to the development of civilization.
Because the inversion layer weakens and inhibits the vertical convection of air, like a thick "lid", which firmly covers the smoke, impurities, harmful gases, etc. suspended in the atmosphere, the inversion layer is also called the "blocking layer" - although the ancients' understanding of the atmosphere is far inferior to ours today, the miraculous thing is that they rely on observation, feeling and intuition to infer that the heavens and the earth are not connected, and the image of all things being blocked, it is actually in line with the actual atmospheric phenomena that occur, which makes people can't help but marvel.
The most significant impact of the "occlusion" of heaven and earth is the decline in air quality and the deterioration of visibility, so the inversion layer often becomes an accomplice to air pollution.
The study found that when the inversion layer appeared, the air near the strata contained a large number of pollution particles, including sulfur dioxide, which seriously endangered human health. Sulfur dioxide with a strong pungent odor is one of the main pollutants in the atmosphere, which will stimulate the respiratory tract, causing people to have symptoms such as poor breathing and chest tightness; sulfur dioxide is inhaled by the human body at the same time as other particulate matter, and it will form a more terrible sulfuric acid mist in the respiratory tract, causing a doubling physiological reaction; soot and dust in the near strata are easy to cause pneumoconiosis and blood poisoning; high concentrations of nitrogen oxides can cause bronchitis or emphysema, and can also damage the central nervous system of the person...
The earliest recorded air pollution tragedies in the 20th century - the Smog Incident in the Maas Valley of Belgium in 1930, the Photochemical Smog Incident in Los Angeles in 1943, the Smoke Incident in the American Industrial Town of Donora in 1948, and the London Smog Incident in 1952 - all occurred under the inversion of temperature, causing millions of lives.
Temperature inversion tends to occur in the morning, evening and night, so the air in these periods is the most polluted. Many people like to exercise outdoors in the early morning, thinking that the air is fresh at this time, but they do not know the opposite. The best time of day for air quality is actually between 10 a.m. and 3 or 4 p.m., and during the "smokey" period in the winter morning and dusk period, you should avoid going out as much as possible.
Woe to the blessed. Although the phenomenon of inversion often aggravates air pollution, it can also inhibit the occurrence of sandstorms to a certain extent because of its obstruction of air circulation. The smooth air flow of the inversion zone is also conducive to the flight of the aircraft.
For some hillsides and river valleys, the inversion zone raises the temperature level in winter, which is conducive to agricultural production, such as the Ili River Valley in Xinjiang, the Sichuan Basin, and the dams of the Yunnan-Guizhou Plateau. The local fruit trees rarely encounter frost damage when wintering, and the fruit is hard and of good quality, which contributes a lot of delicious fruits to people.
"There must be a demon when things go abnormal", the unusual atmospheric phenomenon of temperature inversion is also the "driving force" behind many meteorological wonders, including mirages, advection fog and sea breeze, including the three wonders of the sea, which are inseparable from the role of temperature inversion. The Penglai Wonderland that once fascinated the emperor, and the sea of clouds in the mountains that made the literati poetry flourish, are all small tricks played by the inversion layer.
(The Paper's author: Li Wei, founder of nature education institution Natural Meng.) Illustrator: Ji Jing)
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