Tuesday, January 19, 2010

Frozen Fog and Hoar Frost

Hoar frost after the frozen fog 

I started my day with a look out the kitchen window.   The view was a uniform white, a "white out."  No, it wasn't a blinding snowstorm.   It was what meteorologists call "frozen fog," also known as ice-crystal fog, frost fog, frost flakes, air hoar, rime fog and pogonip.

According to the AMA (American Meteorology Association) glossary of meteorology, "frozen fog is composed of suspended particles of ice, partly ice crystals 20 to 100 μm in diameter, but chiefly, especially when dense, droxtals 12–20 μm in diameter."  Got it?

These definitions may help:

Fog is a cloud (a visible aggregate of minute water droplets) - at the surface of the earth - that reduces visibility below one kilometer.

Frozen fog occurs when these minute water droplets freeze (and reduce visibility below one kilometer). 

 Close up of "hoar frost" on the spruce in my front yard
Frost is the solid deposit of water vapor from saturated air.   

Hoarfrost is the deposit of ice crystals (formed in the same manner as dew - except the temperature of the objects on which it forms must be below 32º F, and the dew point temperature of the air must also be below freezing) on cold objects - trees, branches, poles, fence wire, etc.

It was the ice crystals that got my attention. It was as if all the outdoors had been dusted with a couple of sprays from that "instant snow in a can" stuff used to add a dusting to holiday wreaths and model train sets. 

I didn't realize how difficult it would be to photograph.  It was such a bright morning and everything in my neighborhood was white.

I hope we get the fog again tomorrow so I can give it another try.

Here's a link to an amazing photo of those ice crystals in Washington State.


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