When we describe the coldness of winter, we sometimes like to use the word "feather heavy snow". Speaking of heavy snow, people often think of the forest and sea snowfields in the Northeast. It seems that heavy snow is a product of severe cold areas in high latitudes. In fact, it is not that the colder it is, the easier it is to form heavy snow. We will not go into detail about the specific formation process of snowflakes here, but will briefly talk about the factors related to the formation of heavy snow. In recent years, some scientists have discovered that the crystallization patterns of snow and the size of snowflakes vary greatly depending on the air temperature and the amount of water vapor in the air.
Snowflakes merge multiple times to form snow flakes:
The so-called heavy snowflakes are not actually single snowflakes. Snowflakes fall from the clouds to the ground. The journey is very long, and multiple snowflakes can easily interact with each other. Clinging and merging together, this kind of large snowflake formed by many snowflakes sticking together, or even merging many times, is what we call goose feather snow. The diameter of single snowflake crystals we see falling from the sky is generally 0.5 to 3 mm, but the largest diameter of large snowflakes formed after multiple mergers can reach about 15 mm.
The lower the temperature, the smaller the snowflakes:
The size of snowflake crystals is closely related to the temperature when water vapor condenses and crystallizes. The colder the weather, the lower the temperature, the smaller the snowflake crystals. When the weather is very cold, the diameter of the snowflake crystals formed is often less than 0.05 mm. Meteorological scientists have made this observation: when the air temperature is –8°C to –5°C, prismatic ice crystals are formed; when the temperature is –5°C to –3°C, needle-shaped ice crystals are formed; when the temperature is –3°C to 0°C , generating thin hexagonal plate-shaped ice crystals. It can be seen that when the temperature is -3℃ to 0℃, the shape of snowflakes is the largest and most complete. The snowflake crystals formed in very severe cold are so small that they are almost invisible to the naked eye. Only when they flash in the sun can people see them as fine powder. This kind of snow is called dry snow.
Heavy snow is not exclusive to alpine regions:
Since the 1980s, our country has been in a warmer cycle, and heavy snowfall is relatively rare in many areas. In people's imagination, it seems that only severe cold areas at high latitudes and alpine areas with higher altitudes in winter are the hometown of "goose feather snow". However, many articles point out that when the temperature in the air is below 0℃ and close to 0℃, the ability of snowflakes to merge is particularly large, and it is easy for many snowflakes to connect with each other to form larger snowflakes, which fall down as wet snow. . This statement further illustrates that "heavy snow" is neither exclusive to severe cold areas at high latitudes or high mountain areas, nor is it exclusive to January in severe winter. When our country is in a cold cycle, such as from the 1950s to the 1970s, it is very normal for large-scale heavy snow weather not only in the north, but also in the middle and lower reaches of the Yangtze River. Since the 1980s, our country has entered a warm cycle, but this does not mean that there is no strong cold air in specific years of the warm cycle. As long as steady strong cold air invades our country, even in late autumn and early winter in November, there will be heavy snowfall, such as the heavy snowfall in several northern provinces and cities from November 6 to 7, 2003.
Moisture vapor conditions are very important for the formation of heavy snow:
The better the water vapor conditions, the bigger the snowflakes will be. We know that the water vapor conditions in the air in the middle and lower reaches of the Yangtze River are much better than those in the middle and lower reaches of the Yellow River. Cold air often moves southward, and the scope and amount of snowfall it brings are larger than those in northern areas with lower humidity. Sometimes there is snow all over the sky. , very spectacular, even reaching blizzard level. In January 1955, a heavy snowfall reached a snow depth of 52 and 51 centimeters in Shouxian County, Anhui Province and Nanjing, Jiangsu Province.
The strong cold air process can easily form heavy snow:
It is impossible to snow if the weather is not cold. Otherwise, even if there is snow at high altitude, it will not reach the middle and low altitudes because the temperature is higher than 0℃. It will melt in the air and fall to the ground as rain. Every year, northern my country is affected by cold air earlier, and snow falls first in the northern region. But we know that clouds are where snowflakes are born, and large-scale and deep clouds are where large-scale snowfall occurs, and those steady cold waves or strong cold air moving south provide temperature conditions for heavy snow and even localized blizzards.
The strong dry and cold air lifts a large area of ??warm and humid air to the height of condensation, creating broad and deep clouds, often causing spectacular scenes of thousands of miles of snow and silver covering our country from north to south.