Rime ice

Source: Wikipedia, the free encyclopedia.
Hard rime on a tree
Wind blown rime ice formed on the summit cross of the Fronalpstock

Rime ice forms when

supercooled water droplets freeze onto surfaces.[1]
In the atmosphere, there are three basic types of rime ice:

Soft and hard rime are less dense than clear ice and less adhesive, thus generally cause less damage.

Glaze ice is similar in appearance to clear ice, however it is the result of a completely different process, occurring during freezing rain or drizzle
.

Rime ice also forms when

ice forms on the surface of an aircraft, particularly on the leading edges and control surfaces when it flies through a cloud made of supercooled water liquid droplets. Rime ice is the least dense, milky ice is intermediately dense and clear ice is the most dense. All forms of ice can spoil lift and may have a catastrophic effect on an airborne aircraft. These hazardous effects are due to the ice's ability to disrupt airflow, increase weight, and add drag. Ice forming on propellers or engine inlets are especially dangerous as it can cause severe vibration and/or damage if ingested.[5]

Hard rime

Hard rime on trees in the Black Forest of Germany

Hard rime is a white ice that forms when the water droplets in

windward (wind-facing) side of tree branches, buildings, or any other solid objects, usually with high wind velocities and air temperatures between −2 and −10 °C (28 and 14 °F).[6]

Characteristics

Hard rime formations are more difficult to remove. They have a comb-like appearance, with the streaks of material parallel to that of the direction of the wind. This is unlike

soft rime, which looks feathery or spiky, or clear ice
, which looks homogeneous and transparent.

Scientists at meteorologically extreme places, such as

Mount Washington in New Hampshire, often have to break huge chunks of hard rime off weather equipment in order to keep anemometers
and other measuring instruments operating.

Formation on snow crystals

Electron microscope image of rime ice on both ends of a "capped column" snowflake

Under some specific atmospheric conditions, forming and descending

graupel.[7]

The frozen droplets on the surface of rimed crystals are hard to resolve and the topography of a graupel particle is not easy to record with a visible-wavelength microscope because of the limited resolution and depth of field in the instrument. However, observations of snow crystals with a low-temperature scanning electron microscope (LT-SEM) clearly show cloud droplets measuring up to 50 μm on the surface of the crystals. The rime has been observed on all four basic forms of snow crystals, including plates, dendrites, columns and needles. As the riming process continues the mass of frozen, accumulated cloud droplets obscures the identity of the original snow crystal, giving rise to a graupel particle.[7]

Soft rime

Soft rime
Soft rime

Soft rime is a white ice deposition that forms when the water droplets in light freezing fog or mist freeze to the outer surfaces of objects during calm or light wind. The fog usually freezes to the

windward
side of solid objects, particularly those with a likeness to that of tree branches and wires.

Soft rime is similar in appearance to

relative humidity (above 90%) and temperatures
below −8 °C (18 °F).

Soft rime formations appear as narrow white icy needles and scales. These needles are fragile and can be easily shaken off objects and removed. Factors that favour soft rime include: small drop size, the slow accretion of liquid water, a high degree of supercooling, and fast dissipation of latent heat of fusion. The opposite of these conditions favour ice with higher densities, such as the aforementioned

hard rime or clear ice
.

See also

References

  1. ^ WMO. "Rime". International Cloud Atlas. Retrieved 2025-02-25.
  2. ^ "What is Soft Rime?". Earth.com. Retrieved 2025-02-25.
  3. ^ a b L, Machelle (2018-03-15). "What Is Hard Rime and Soft Rime?". WeatherEgg®. Retrieved 2025-02-25.
  4. ^ "What is Hard Rime?". Earth.com. Retrieved 2025-02-25.
  5. ^ "Icing Hazards". www.weather.gov. Retrieved 2025-02-25.
  6. ^ WMO. "Hard Rime". International Cloud Atlas. Retrieved 2025-02-25.
  7. ^ a b Rime and Graupel, Electron Microscopy Unit, Beltsville Agricultural Research Center, U.S. Department of Agriculture., archived from the original on 1 May 2012, retrieved 25 August 2012
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.

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