Friday, January 23, 2009

Hoar frost vs rime frost


Rime frost (L) and hoar frost (r)

Once I get out of the city, I spend about 20 minutes on the freeway before turning onto a smaller highway that takes me through lake country to get to Franconia. It's this last section of the drive that I enjoy the most every morning. Lakes, farmland, small towns...it's always interesting.
Yesterday, I drove right into dense fog. You could see it rolling over you and as I went up and down the small hills, it would grow less thick and then surround the car once again. And every single thing in the landscape was lined out with frost: fence, grass, twig, and bark. The word "rime" came back to me....rime frost....and I wondered if that was the correct term for this particular frost or if it was "hoar" frost.

I've done a little research this morning on the different kinds of frost. It turns out that I was correct. Rime is often the result of dense fog, caused by millions of water droplets in the air freezing on contact with a surface that has been cold for a very long time. In northern England, they call it "snowcrumb." Both terms are lovely. Hoar frost, if you're interested, is spikier than rime...more like thorns and long crystals. It occurs on cold clear nights when the air becomes warmer than the trees and fences. Now I am somewhat knowledgeable about frost.

1 comment:

Anonymous said...

If you have been hiking in an alpine area above the tree line, during winter, you most likely see hoarfrost collecting on the needles of conifers.