NATURE NOTES - A frosty reception

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WE WERE out in the woods on our weekend wander and it was absolutely freezing!

The sky was the palest blue with not a cloud to be seen – the sun was doing its best to warm us but the wind was one of those lazy ones that blows straight through you instead of going round.

It was incredibly quiet, we stopped a few times to listen if we could hear any birds but not a thing. They must have been all ‘utched’ up to one another keeping warm.

The ground was very noisy though – the frost had set hard and every time you put a foot down it made a lovely ‘crunching’ sound.

The majority of trees had decided that they had had enough of their leaves and most were now on their way to being bare. The fallen leaves had all been dusted by frost – looking more like icing sugar – and the sun made them sparkle like the very best Christmas decorations.

I was joking with the girls saying that Jack Frost had been and sprinkled them during the night. Who? Says Tanith.

I explained that Jack Frost is a figure believed to have originated in Viking folklore, an elfish type of creature who personifies crisp, cold, winter weather. Jack is said to leave those frosty crystal patterns on leaves and windows on cold mornings to remind us that it is his time - Winter. It is also thought that we derived the name Jack Frost from the Norse character names, Jokul (icicle) and Frosti (frost).

Other cultures had frost beings too. Frost Woman and Frost Man were weather deities in Finland and northern Russia. They controlled cold weather events in their domains, from frost to blizzards. In another part of Russia, Father Frost was a blacksmith who forged chunks of ice and sent them to Earth. The Germans had Mother Frost, who shook white feathers from her bed which fell on Germany as frost and snow.

In reality frost most often forms on cold, clear windless nights, or nights with very light winds. The air temperature near the ground falls below frost point - the temperature to which air must be cooled (at constant humidity) to achieve saturation with respect to ice at or below 0 C. Interestingly, this can happen when the air temperature is above freezing.

Frost forms first on rocky, glass and metal surfaces, things that lose heat most quickly.

That is why you will often have your car windshields frosted over while there is no frost on the surrounding ground.

There are two forms of frost: rime and hoar. Rime frost occurs when the rate of frost formation is rapid, usually under conditions of high water content in the air (vapour and/or liquid) and at least moderate wind speeds.

Rime formation is common during fogs where supercooled or near-freezing water droplets come in contact with subfreezing surfaces.

Rime frost has a grainy appearance, like sugar or salt, forming spikes, needles, or feathers and not having a recognizable crystal structure.

Rime is opaque, less transparent than glaze ice formed during freezing rain episodes. Rime is denser and harder than hoar frost.

But I still prefer to think that Jack Frost has been a calling!