Why are there traces of snowflakes on the window?

The one on the window should be called ice flower.

"Ice flowers" are often formed only on the inner surface of glass windows. In cold winter, the temperature difference between indoor and outdoor is large. Indoor water vapor with high temperature condenses directly into solid when it is cold on the inner surface of door and window glass, forming ice flowers, while outdoor water vapor with low temperature is not easy to condense on the outer surface of glass.

When ice crystals form ice on the eaves in flying snowflakes, this rare hexagonal snowflake is called flying snow ice flower. This kind of ice is very rare, only once every 10 years on average!

Ice flower, also known as weiyang flower, is a beautiful crystal that sticks together to form snowflakes in the process of falling. The size of a single snowflake is usually between 0.05 and 4.6 mm, and the snowflake is very light, with a single weight of only 0.2-0.5 g. No matter how small a snowflake is, it is wonderful. Its crystals are all regular hexagons. Therefore, the ancients said that "there are five flowers in vegetation and six snowflakes".

Why are snowflakes mostly hexagonal and have so many patterns?

Snowflakes are formed by magnifying small ice crystals, and the molecules of ice are mostly hexagonal, so snowflakes are mostly hexagonal. The diversity of snowflake shapes is closely related to the water vapor conditions when it is formed.

For hexagonal flake ice crystals, due to the bending degree of their surfaces, sides and corners,

ice flower

Different, corresponding to different saturated vapor pressures, the saturated vapor pressure at the corner is the largest, followed by the edge, and the plane is the smallest. When the actual vapor pressure is the same, the growth of sublimation is different because of the different saturated vapor pressures on the surface, edge and corner of ice crystals. If the water vapor in the cloud is not very rich, the actual water vapor pressure is only greater than the saturated water vapor pressure on the plane, and the water vapor only condenses on the surface, then a columnar snowflake is formed; If there is a little more water vapor, the actual water vapor pressure is greater than the saturated water vapor pressure at the edge, and the water vapor will condense at the edge and surface. Because the speed of condensation is also related to the degree of bending, the place with a large degree of bending will condense faster, so the condensation at the edge of ice crystals is faster than that on the surface, and more flake snowflakes will be formed at this time; If the water vapor in the cloud is rich, and the actual water vapor pressure is greater than the saturated water vapor pressure on the corner, then there is water vapor condensation on the surface, edges and corners, but the sharp corners are prominent, and the water vapor supply is the most sufficient and the condensation grows fastest, so many branches or star-shaped snowflakes are formed.

Coupled with the constant movement of ice crystals, their temperature and humidity conditions are constantly changing, which makes the growth rates of various parts of ice crystals inconsistent and forms various snowflakes.