A Guide to the different Forms of Frost

Frost is formed when surfaces are cooled to the dew point of the air.  It occurs when the air and surface is both below zero temperatures.  The size of crystals contained within the frost depends upon a few factors.  The temperature, the amount of time it is left to accumulate, and the amount of water vapour all have an influence on what type of frost is created.  There are many different types of frost, and they all take on different forms.  Frost is more interesting than you may think, it is unique in how it is formed.

* Rime *

This is a form of frost that is made when the air is heavily saturated and in very windy conditions.  Rime may be present on ships traveling through the Arctic sea, it appears as an icy solid mass on the ships rigging.  Rime usually has to have a surface that has a lot of condensation on it before it starts to form.

* Advection Frost *

You can see this frost in the form of spikes on branches, trees, poles, and other surfaces. It looks like a rim around the edges of plants and leaves, it can form during the day or at night time.  A really cold wind is usually blowing for this type of frost to form.

* Hoar Frost *

Also known as radiation frost this happens when ice crystals are deposited on the ground or other objects.  This type of frost is apparent on cold clear nights when heat causes objects to become colder than the air.  The frost is below freezing temperatures even though the surrounding air may not be.  Hoar is what causes avalanches when it forms on top of snow.  A light wind is usually preferable to form this type of frost, if the wind is too strong it will destroy the ice crystals.  Hoar can also be present in man-made areas, such as household freezers or rooms where humidity and moisture are allowed to enter.  The effect of hoar frost is instant, it forms rapidly, and can occur anywhere that is not properly insulated. 

* Window Frost *

This frost is also known as fern frost, because of the patterns it produces during the formation process.  It appears when a glass pane is exposed to cold air on the outside, while the air inside is moist.  The bottom part of the glazing is usually colder than the top part, that’s why frost usually forms on the bottom and sometimes doesn’t appear on the top of the pane.  Even with double panes this frost can still be present due to air convection between the two panes of glass on very cold days. 

During freezing weather conditions frost flowers can be formed.  These are a unique site and normally only last for a day.  This happens when water within the plant stem erupts causing the stem to crack.  Water goes out from the cracks and freezes on contact with the air. This form of frost can actually look like a flower, this is a very rare form of frost to observe.  As you can see there are many different types of frost and not just the plain old frost you see on your car window.   Frost can cause problems, but it is also interesting to know the different varieties that are produced.