What's the difference between rime and frost?

Rime, commonly known as ice flower and tree hanging, is a milky white ice crystal deposit formed by direct condensation of water vapor in the air at low temperature or direct freezing of supercooled water droplets on objects. This is a very rare natural wonder.

Rime is not ice or snow, but the result of fog on branches and other objects freezing below zero degrees Celsius and viscous water vapor piling up with the wind, which shows as white opaque granular structure deposits. The formation of rime requires low temperature and sufficient water vapor, and it is even more rare to have these two extremely important and contradictory natural conditions for the formation of rime.

Formation principle

Rime is a kind of white or milky opaque ice layer attached to the windward surface of ground objects (such as branches and wires). It is also formed by condensation of supercooled water droplets. When supercooled water droplets (temperature below zero) collide with objects also below freezing point, rime will be formed. When the water vapor in the air touches an object, it immediately condenses into a solid state, and a rime layer or rime deposit will be formed.

The conditions for the formation of rime are very harsh. First of all, the winter is cold and long, and there is enough water vapor in the air. Secondly, the formation of rime requires both sunny days and partial cloudy days, as well as calm, or the wind speed is very small. Clouds in the sky are like quilts of the earth. When there are clouds at night, the outward long-wave radiation is weakened, which makes the ground temperature drop slowly and the temperature difference between day and night is relatively small, so that the water vapor in the air near the ground will not condense. If this quilt is lifted, it will emit more heat, lower the ground temperature and provide the necessary conditions for water vapor condensation.

Strong wind is the natural enemy in the process of rime formation, which can always blow away the ice crystals with loose structure in the process of rime formation. Even if the rime gathers together, it will be blown away without a trace, and the conditions of small wind or still wind provide a guarantee for the condensation of water vapor into rime. Generally speaking, in winter, sunny days are unlikely to appear at the same time as still winds or breezes. In addition, when there is supercooled fog, it is especially beneficial to the growth of ice crystals on ground objects. At this time, white ice flowers are formed on wires and branches, which is called "rime". When there is fog and the temperature is higher than 0℃, fog drops stick to leaves or other objects, which is called "fog condensation" and is most common in forests.

Trait characteristics

Rime is a kind of white or milky opaque ice layer attached to the windward surface of ground objects (such as branches and wires). Because there are many gaps between water droplets in the rime, the rime is completely opaque white. The rime is pale and white, attached to trees and objects, just like a silver flower of a tree, delicate and elegant. This is the tree hanging (also known as the snow hanging).

Rime has two main shapes. One is that supercooled water droplets quickly freeze into small ice cubes after hitting cold ground objects, which is called particle rime (or hard rime) and has a relatively compact structure. The other is the crystalline rime (or soft rime) formed by the condensation of water vapor generated when water droplets evaporate, which has a loose structure and will fall off with a slight vibration.

Frost is mainly formed on clear and quiet nights, while rime can be formed at any time of the day, usually on foggy cloudy days. Frost is formed on the horizontal surface of an object, while rime is mainly formed on the surface of an object or on the surface perpendicular to the ground. Wusong is good for crops, but frost is bad for crops.