Rime

From HydroWiki

Rime is a white deposit of very small supercooled cloud droplets that freeze rapidly when they come in contact with an available surface. Rime will accumulate on existing rime ice parallel to the wind direction on the windward side of objects.

Rime appears flakey, brittle, and opaque white. The supercooled water vapor freezes very rapidly and air is trapped between the ice crystals, causing it to have a low density and weak structure. A change in wind direction or force on rime can break it away from the surface easily. Rime ice is one of the most common forms of ice on airplanes and poses little threat to pilots due to the ease of removal, but it can still be hazardous by reducing lift if accumulation is significant.

The rate of growth of riming can be significant if temperatures are favorable. Rime will usually form when the temperature is below freezing. Generally low moisture is sufficient for rime to occur, due to the small drop size.

Rime on a tree in the White Mountains of New Hampshire

Photo taken by R Cloutier (use with permission)

Rime tends to form in alpine areas and will be found coating all surfaces, such as trees. Suspended droplets travel freely though the atmosphere until a surface becomes available to freeze on. On top of Mt. Washington rime can be seen for most of the winter. Instruments atop of the mountain must be monitored to prevent accumulation of rime.

Links: Mt. Washington Observatory

References:

Glossary of Meteorology

http://amsglossary.allenpress.com/glossary/search?id=rime-ice1

http://amsglossary.allenpress.com/glossary/search?p=1&query=rime

--R cloutier 13:15, 9 February 2007 (EST)