BLOG: Rime Ice versus Frost - | WBTV Charlotte

BLOG: Rime Ice versus Frost

(Crandall Sims | WBTV) (Crandall Sims | WBTV)

This past weekend, our 7 p.m. News Producer, Crandall Sims, journeyed up to our North Carolina mountains and came back with these delightful shots of the numerous ice-covered trees that decorated the Blue Ridge. 

At first glance, one would probably assume we’re looking at frost, but not quite. 

Frost forms on objects when water vapor (an invisible gas) forms ice crystals directly on a surface, or nucleus. It is also known as deposition, ice nucleation or desublimation. 

See Leigh Brock’s Blog from a few Blogs ago for more on frost formation.  

In the case of rime ice, liquid must already be present in the air. That of course is typically found as tiny water droplets hovering in low clouds and fog. Tiny water droplets can actually exist in below-freezing air without solidifying. These are known as super-cooled water droplets.

The microphysics behind this phenomenon are still being debated, but what is well understood is this: The only way they can exist is in the absence of a seed, that is, any particle or nucleus in the air with which the droplet can combine. Once these supercooled droplets come into contact with a solid object, or surface, they freeze instantly. 

Those are the crystals you see forming on the trees in the accompanying pictures as the clouds drifted by.  

Notice also in some of the pictures the sharp cutoff of ice. That is either due to the clouds not getting any lower, or the fact temperatures were still above freezing from that point downward.

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