Sunday, 8 January 2017

Post 453 - Fabulous Frost

A crisp frosty walk in Silton forest
Hey everyone, today's Post 453 and I think it's the perfect time to do this post. As it's early in the New Year now and Winter is well underway it's definitely right to do my first ever post on frost. It's not been that wintery yet where we are but over the Christmas holidays there were a few days when we went for walks where there was quite a bit of frost. I've probably covered frost slightly in some of my Patterns in Nature posts, but I don't believe I've done one completely on frost, so in this post I'm going to say how frost is formed, and what it is.

So, what is frost?

Frost even brings out the patterns in a pile of leaves.
What most people know about frost is that it's ice crystals formed after a cold snap. Frost only forms if the temperature is below freezing, and there has to be moisture in the air. If it is dry you can get sub zero temperatures without frost. Frost forms when the moisture in the air changes directly from gas to solid.

Frost is renowned for being one of the most beautiful natural occurrences. The patterns it can make on leaves for example are beautiful. There are lots of different types of frost, which I have listed below with their definitions:

Advection Frost - is tiny ice spikes that are created when there is a very cold wind blowing over branches of trees, poles and other high up surfaces. Usually it forms against the direction of the wind. It can occur at any time, Day or Night.

Frost up close - here its formed icy tubes
Air Frost - when the air temperature is below freezing and there is water in the atmosphere ice crystals form. Generally an air frost forms on surfaces a metre above the ground.

Ground Frost - similar to an air frost but ice crystals form on the ground. Sometimes the ground can cool quicker than the air so you can get ground frosts without an air frost.

Some crystals were amazingly long!
Hoar Frost - This is where white ice crystals are deposited on the ground. They form on cold, clear nights when the conditions let heat radiate out to the open sky faster than other sources (such as wind or warm objects) can replace it. The name 'Hoar' comes from an Old English adjective that means something is showing signs of old age. In this context it means the frost makes trees and bushes look like white hair!

There are also several different sub-types of Hoar Frost:

  • Air Hoar is a deposit of Hoar Frost on objects ABOVE the ground, such as tree branches, plant stems, and wires.
  • Surface Hoar is fern-like ice crystals directly deposited on snow, ice or already frozen surfaces, usually ON the ground.
It made this plant look like a crystal chandelier
  • Crevasse Hoar consists of crystals that form in crevasses where water vapour can accumulate in calm weather conditions. This is IN the ground.
  • Depth Hoar refers to cut crystals that have slowly grown bigger within caves UNDER banks of dry snow. Depth Hoar crystals keep growing, seemingly consuming neighbouring smaller crystals.

White Frost - Is a rare type of frost that forms when the humidity is over 90% and the temperature is below -8*C and it grows against wind direction.

A bramble branch with new icy spikes!
Window Frost - This is a formation of amazing looking crystals that can be found on windows, such as car windscreens or house windows. Water vapour condenses on the glass forming frost patterns.

There are also phenomena called Glaze and Rime which are slightly different. They are formed when supercooled fog or drizzle come into contact with surfaces. Rime forms on vertical surfaces and glaze forms on the ground - sometimes known as Black Ice.

The best I could do to capture the frosty sparkle
One of the things I like about frost too is the folklore of Jack Frost - the mischievous character that paints the ice patterns on windows and nips the noses of people on cold days! Jack Frost seems to have been around in folklore since the 1700's but there are lots of other myths in other cultures associated with winter. In Norse mythology Ullr was the god of winter, son of a frost giant and ruler of Asgard in Odins absence in winter. In Russia there is a Father Frost. He's a bit different to Jack Frost as he is essentially their Santa and he delivers the presents helped by a Snow Maiden.

I didn't know nearly as much as I did about frost as I do now! I didn't know there are types of frost that could grow in the day, or that there was even more than one type of frost.

Hope you enjoyed,