Autumn Returns

We had a touch of winter in the last spell. Now we are back in Autumn. …

Britain gets little snow fall in winter. Years that supply a couple of weeks of deep snow are exceptional and long remembered -even in Scotland.

Most of the time and through November too, we get seasons of mellow fruitfulness:

To Autumn

Season of mists and mellow fruitfulness, close bosom-friend of the maturing sun;
Conspiring with him how to load and bless with fruit, the vines that round the thatch-eaves run;
To bend with apples the mossed cottage-trees and fill all fruit with ripeness to the core;
To swell the gourd and plump the hazel shells with a sweet kernel.
To set budding more and still more, later flowers for the bees, until they think warm days will never cease,
For Summer has o'er-brimmed their clammy cells.

Who hath not seen thee oft amid thy store?
Sometimes whoever seeks abroad may find thee sitting careless on a granary floor, thy hair soft-lifted by the winnowing wind; or on a half-reaped furrow sound asleep, drowsed with the fume of poppies, while thy hook spares the next swath and all its twined flowers.
And sometimes like a gleaner thou dost keep steady thy laden head across a brook;
Or by a cider-press, with patient look, thou watchest the last oozings hours by hours.

Where are the songs of Spring? Ay, where are they?
Think not of them, thou hast thy music too, —while barred clouds bloom the soft-dying day and touch the stubble-plains with rosy hue.
Then in a wailful choir the small gnats mourn among the river sallows, borne aloft or sinking as the light wind lives or dies.
And full-grown lambs loud bleat from hilly bourn;
Hedge-crickets sing; and now with treble soft the redbreast whistles from a garden-croft and gathering swallows twitter in the skies.

John Keats.

So that is how it is supposed to be.

Every so often we are treated to a weather system that mixes anticyclonic weather with cyclonic. If they are both based at latitude 60 or so degrees north, either side of the Greenwich meridian (more or less) they drag down from the icy north, weather that is loaded with wet snow.

Having set the parameters, it is a small matter to fixate on the wish list for snowy winters:

Anticyclonic stuff over Scandinavia. The Scandi-High.
And markedly Low pressure at Iceland. The classic Icelandic Low.
You'd think that wouldn't be too hard to arrange wouldn't you?

The Icelandic Low forms when low pressure moves out of North America.
Inevitably such weather travels out between the latitudes of the Carolinas and the Great lakes. And gathers at Newfoundland.

I say gather because it seems that there is an habit for a solitary Low to wait until it is joined by another before making a leap into the ocean.

And it seems to follow the bathymetry of the oceans too. There is some sort of a furrow. I hate to use the word trench. (Lows follow shallow waters if they can, even in the tropics.) Quite often a Low will find the furrow that runs some way towards the coast of North America from Iceland.

It doesn't go all the way, as far as I can tell but a large part of it is certainly seen on any sea floor map of the area. It runs in a straight line from the southern shore of Iceland on a tangent to the east coast -once it passed through the channel between Newfoundland and what used to be called Labrador.

As an extra coincidence -if coincidence it be, the Appalachians run in a line that will take you along the path these northern lows tend to follow.

Any tendency is more than a coincidence. If it is a regular occurrence and defies explanation, it is wise to cast about for less pragmatic mechanisms than classical fluid mechanics. If it occurs despite whatever weather systems are already ahead of it then the reason is that the cause is more powerful than the vapid atmosphere.

But I digress.

These Lows, having built up enough steam to move out east, are halted on the Mid Atlantic Ridge until they are strong enough (or allied with others to be strong enough) to cross from just south of Iceland. That is the story of the Icelandic Low.

Well that's my story of it at any rate.

I don't know the origin of the Scandi High. I had been collecting graphics from Russia that shows where Atlantic Lows enter Russian and spread out over Europe and Asia. North of Siberia they filter out their composites and come ashore one at a time or even together but at different locations.

The server is too slow and irritating for me to cope with it as I am a very impatient man with no sticking power and a very short attention span.

Maybe I aught to rethink this.

Edit:

I thought I had it the wrong way around:

Highs seem to step into the Baltic overstepping Britain for some reason. And once in the Baltic (or that region generally) they build up I know not how.

The snow on this instance however had come from a brief period where Greenland and Iceland had a well defined High spun off from the Azores. Again I don't know how it was maintained but while it lived, there was a marked low to match it.

This situation rarely lasts long and the difficulty it seems to have in forming would explain the rarity of snow here.

Cyclones spin in the opposite direction to anticyclones.
Where they meet there is a stream of both cold and warm air flowing in the same direction.
It is this stream that brings Britain its snow.

I dare say that in North America it is the cause of devastating ice storms. Where low pressure areas are less humid and thus capable of supercooling.

Clean air, if it is cold enough, can maintian vapour as water down to temeratures as low as 40 degrees. Once it mixes with something it can form ice on, it falls out of suspension like wet concrete.

Back soon.
I shall return.

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