Thursday, March 19, 2009

Frost & Hoarfrost

Just before this latest cold snap that has produced some nice window frost designs we had a day of freezing fog. This fog created hoarfrost on some of the willow bushes that were still sticking out of the deep drifts around the house.
The main difference between the two is window frost forms on a pane of glass when exposed to below freezing temperatures on the outside and moist air on the inside room. Water vapor from the air condenses as frost on the inside surface of the window pane. Crystal growth is strongly influenced by scratches or other film on the window and can grow into elaborate patterns. (photo 1)

Hoarfrost develops when water vapor condenses directly into ice on out side objects such as twigs or grass stems. When the frost forms minute ice crystals covering the ground it is just called frost. But if the frost grains grow larger they are called hoarfrost crystals. (photo2)

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Arctic Smoke Signals by James W. Helmericks is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 United States License.