by Winter Chestnut

Created on: January 04, 2010

Hoarfrost Playground

     Something charming and wonderful happens as the children sleep, all warm and cozy in clouds of snuggly blankets.  Outside, where the sky is clear and dark, Jack Frost is about, not bothered by the cold, creating a playground of ice crystals, all thick and white.  The children awake, rubbing sleep from their eyes, and gaze out with wonder and curious delight. "Could this be snow?" Excitement fills the room as questions abound.

     Sipping coffee, a reply, with a smile of good cheer, "No, little ones, not today.  Jack frost has been at play. What delights the eyes on this cold and bright morning, is hoarfrost."

     As breakfast is cooking, explanation will be needed. What Jack Frost has created is a beautiful ice crystal park, waiting for exploration.  With coats and scarves, the children head out, and giggles are heard between the crunching of grass.

     What creates this magical place of sparkling crystals? What is this hoarfrost?

     The air outside is full of moisture, supersaturated, meaning more water is in the air than the air can carry.  As the temperature drops, the humidity decreases to 100%.  This is known as the dew point.  As the temperature continues to fall, moisture comes through as rain, snow, dew or hoarfrost.

     On clear and cold winter nights, hoarfrost is spread about much like the dew that visits in the spring time. The difference between dew and hoarfrost is the temperature of the object on which the hoarfrost forms. The object, be it a leaf, a tree branch, or pole, is well below 0 degrees Celsius in the formation of hoarfrost.  Hoarfrost forms from tiny ice crystals, which often start at the tips of plants or other objects.  The ice crystals interlock, building layer upon layer, that can resemble snow.

     Sometimes, hoarfrost develops from liquid dew that has frozen, following a sudden drop in temperature.  This is known as silver or white frost.  Usually, the dew drops do not freeze immediately, unless the temperature is below zero degrees Celsius. Otherwise, the dew droplets are first supercooled.  Eventually, the droplets will freeze, if the temperature falls below -3 degrees Celsius to -5 degrees celsius.

     Hoarfrost might also appear from sublimation, or when the water in the air, known as water vapor, forms ice directly on the surface of an object, skipping the liquid phase.  Instead of the water molecules flowing from gas, to liquid, to sold, the molecules are converted from gas to solid, which are the ice crystals of hoarfrost. 

     Hoarfrost is usually formed from a combination of processes, suppercooling, and sublimation.  Layers build up and remain as long as tempertures allow.

     Hoarfrost is well worth the venture into the cold.  The amazing crystals appear as needles, cups, plates,  can appear fern-like, and feather-like, depending on the temperature at which the crystals were created.

     Jack Frost truly did come out to play, and create a magical playground of crystals and ice.  It's a beautiful day for a hoarfrost playground.

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