Tuesday, 7 December 2010

Hoare Frosts.



For those from warmer climes, you could be forgiven for thinking this is just another series of photographs of snow; the UK is suffering from an abundance of the stuff at the moment.....but it isn’t.

We don't have any snow in my town, yet the world is white.



It’s something called hoare frost. (sometimes spelt without an e on the end) It is truly spectacular.

 
When it’s cold and frosty at night in winter, and the skies are clear, crystals form on vegetation or anything that has been chilled below freezing point. It was -12 last night and was still -6 at lunchtime so the world for us is not covered with snow but with hoare frost.







The interlocking ice crystals become attached to the branches of trees, leaves, hedgerows, grass etc, and if you look closely you can see fine feathers or needles of ice crystals. They fall off just like snow, if caught in the breeze.

Heres a bit of technical stuff downloaded from a weather website.

The relative humidity in supersaturated air is greater then 100% and the formation of hoar frost is similar to the formation of dew with the difference that the temperature of the object on which the hoar frost forms is well below 0°C, whereas this is not the case with dew. Hoar frost crystals often form intitially on the tips of plants or other objects.

Hoar frost might form as liquid dew that has subsequently frozen with a drop in temperature, which is then known as silver frost or white frost. Usually the dew drops do not freeze immediately, even if the air temperature is slightly below zero. Rather they become supercooled dew droplets at first. 

Supercooled dew will eventually freeze if the temperature falls below about -3°C to -5°C. Hoar frost deposits might also derive by sublimation, when water vapour is forming ice directly on the surfaces concerned. In most cases hoar frost will have formed by a combination of the processes above. 


4 comments:

  1. Lots of people round here have been using Hoar frost, I was too polite to ask what it meant so thank you. The pictures are fantastic. Hope you're keeping warm.

    ReplyDelete
  2. I love seeing all the frost on the vegetation but I dont like having to go to work on the very icy roads, the after effects of the heavy snow last week.

    ReplyDelete
  3. That is so pretty but, sat here on a balmy 15C day in Rome, I'm not especially jealous xxxxxxx

    ReplyDelete