What's the weather like with ice needles?

Ice needle: tiny flake or shape ice crystals floating in the near-surface atmosphere. Shining in the sun can be distinguished, and sometimes other weather phenomena such as solar pillars or solar halos can be formed in the sky.

In meteorology, the scientific name of needle snowflake is "ice needle", which belongs to a relatively rare weather phenomenon. Needle-shaped snowflake has only one scientific name, but there are many nicknames, such as Luomian Snow, Iced Silver Needle in Li Mochou, Pear Flower Needle in Rainstorm, Monosodium Glutamate and Long-grain Fragrant Rice.

It often occurs in the cold (the temperature is about -35℃ ~-20℃) late at night or early in the morning, and it often appears in the cloudy weather of blue sky or breeze. At this time, the humidity of the near-surface atmosphere is higher than the saturation and humidity of the ice surface, and a small amount of ice crystals are produced and grow under the action of ice cores.

Formation of ice needle

Needle snowflakes must be formed in very cold weather conditions, and the temperature is generally below -5℃. This does not refer to the ground temperature (what we usually call the temperature), but to the temperature of the air that makes needle-like snowflakes. In addition, the ground temperature should not be too high, and the height should be below 0℃, otherwise it will melt before landing.

High-altitude water vapor will form tiny ice crystals when it is cold. However, if the air environment is too dry and the humidity is much lower than the surface humidity of ice crystals, then the ice crystals will soon sublimate and disappear. However, if the humidity of air environment is very high, which exceeds the saturation humidity of ice crystals, then ice crystals will sublimate, and water vapor will condense on the surface of ice crystals, increasing the quality of ice crystals.

When the mass of ice crystals increases to a certain extent, they can't suspend in the air and start to move downward, so water vapor condenses on the vertical plane of the ice crystals, and the ice crystals become longer and longer, and finally become long "ice needles".