Frosts

Well, last week was up and down in temps from -5oC then at weekend 9oC!! The weather peoples are predicting ‘a harsh winter with record low temperatures’ – will have to see what happens. It seems every year they predict harsh winters and then mad hot summers!! I remember well ‘there will definitely be no hurricane winds’ statement in 1986 the night before the worst winds this country had seen for centuries!!!! A friend who is into Astrophotography was telling me that there has been no sun spot activity of late which is usually an indicator of something odd weather-wise will follow – so we’ll see what happens.

I still gat totally fascinated by the early morning frost that had bejewelled the leaves and even more amazed that these tiny jewels ‘vanish’ if touched or breathed.

I’ve mentioned before that Jack Frost (who according to legend) 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 out with his bag of ‘ice jewels’ spreading them far and wide over the landscape!!! Fingers crossed he visits again just before Christmas and brings Mother Frost with him so she can give a lovely festive sprinkling of snow!!