Frost crystals also grow from water vapor, except they grow close to ground and on window panes, grass, the stuff in our freezer -- basically any solid surface that is exposed to cold air and water vapor. Let's explore the main types of frost.
When our window panes are exposed to cold air and water vapor (basically every night during the winter!) frost is born. It occurs when one side of the glass is open to below-freezing temperatures (the outside) and one side is open to warm moist air (the inside). The water vapor that is hangin' out in the inside air begins to condense into frost on the cold glass. Frost forms through the same crystal growth processes as snow, only because they are on such smooth surfaces, the results are different.
graphics/window_frost.jpg
When water vapor immediately condenses into liquid water, you get a)raindrops or b)dew. But when the water vapor immediately condenses into ice, you get a)snowflakes or b)FROST! However, you cannot call frost simply frozen dew, because frost forms as microscopic ice crystals that cover the ground. And sometimes, the frost grains become larger, in which case they are Hoarfrost crystals. The most common kind of hoarfrost is called Surface Hoar. This frost grows usually overnight on snowbanks. The "sparkles" that you see when you look out on a field of snow? It's actually surface hoar frost.
"Surface hoar forms when a snowbank warms up during the day and is then cooled again overnight.� The night air cools the surface of the snowbank more than the inside, so that water can evaporate from inside the snowbank and recrystalize on the surface.� By morning the snowbank is covered with a layer of faceted ice crystals, and they can be quite large.� These usually melt again once the sun comes up, so the best time to find surface hoar is early in the morning." (http://www.its.caltech.edu/~atomic/snowcrystals/frost/frost.
htm)
http://www.kpbsd
.k12.ak.us/solel/
pfitzysfishys/12
1300/images/hoar
frost.jpg
http://www.its.
caltech.edu/~a
tomic/snowcry
stals/frost/frost.
htm
