Soft rime
Encyclopedia
Soft rime is a white ice
deposition that forms when the water
droplet
s in light freezing fog
or mist
freeze to the outer surfaces of objects, with calm or light wind. The fog freezes usually to the windward side of tree branches, wires, or any other solid objects.
Soft rime is similar in appearance to hoar frost
; but whereas rime is formed by vapour first condensing
to liquid droplets (of fog, mist or cloud) and then attaching to a surface, hoar frost is formed by direct deposition from water vapour to solid ice. A heavy coating of hoar frost, called white frost, is very similar in appearance to soft rime, but the formation process is different: it happens when there is no fog, but very high levels of air relative humidity
(above 90%) and temperature
s below −8 °C (18 °F).
Soft rime formations have the appearance of white ice needles and scales; they are fragile and can be easily shaken off objects.
Factors that favour soft rime are small drop size, slow accretion of liquid water, high degree of supercooling, and fast dissipation of latent heat of fusion. The opposite conditions favour ice with higher densities, such as hard rime or clear ice
.
Ice
Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...
deposition that forms when the water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
droplet
Drop (liquid)
A drop or droplet is a small column of liquid, bounded completely or almost completely by free surfaces. A drop may form when liquid accumulates at the lower end of a tube or other surface boundary, producing a hanging drop called a pendant drop...
s in light freezing fog
Fog
Fog is a collection of water droplets or ice crystals suspended in the air at or near the Earth's surface. While fog is a type of stratus cloud, the term "fog" is typically distinguished from the more generic term "cloud" in that fog is low-lying, and the moisture in the fog is often generated...
or mist
Mist
Mist is a phenomenon of small droplets suspended in air. It can occur as part of natural weather or volcanic activity, and is common in cold air above warmer water, in exhaled air in the cold, and in a steam room of a sauna. It can also be created artificially with aerosol canisters if the...
freeze to the outer surfaces of objects, with calm or light wind. The fog freezes usually to the windward side of tree branches, wires, or any other solid objects.
Soft rime is similar in appearance to hoar frost
Frost
Frost is the solid deposition of water vapor from saturated air. It is formed when solid surfaces are cooled to below the dew point of the adjacent air as well as below the freezing point of water. Frost crystals' size differ depending on time and water vapour available. Frost is also usually...
; but whereas rime is formed by vapour first condensing
Condensation
Condensation is the change of the physical state of matter from gaseous phase into liquid phase, and is the reverse of vaporization. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition....
to liquid droplets (of fog, mist or cloud) and then attaching to a surface, hoar frost is formed by direct deposition from water vapour to solid ice. A heavy coating of hoar frost, called white frost, is very similar in appearance to soft rime, but the formation process is different: it happens when there is no fog, but very high levels of air relative humidity
Relative humidity
Relative humidity is a term used to describe the amount of water vapor in a mixture of air and water vapor. It is defined as the partial pressure of water vapor in the air-water mixture, given as a percentage of the saturated vapor pressure under those conditions...
(above 90%) and temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
s below −8 °C (18 °F).
Soft rime formations have the appearance of white ice needles and scales; they are fragile and can be easily shaken off objects.
Factors that favour soft rime are small drop size, slow accretion of liquid water, high degree of supercooling, and fast dissipation of latent heat of fusion. The opposite conditions favour ice with higher densities, such as hard rime or clear ice
Clear ice
Clear ice refers to a solid precipitation which forms when air temperature is between 0 °C and -3 °C and there are supercooled, relatively large drops of water...
.