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| 30 Apr 2008 04:19:44 pm |
 Ice Terminology |
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There is an internationally accepted terminology for ice forms and conditions.
General Terminology
The following terms are the ones commonly used in the preparation of the Canadian Ice Service products and publications.
Sea-ice types
New: A general term for recently formed ice which includes frazil ice, grease ice, slush and shuga. These types of ice are composed of ice crystals which are only weakly frozen together (if at all) and have a definite form only while they are afloat.
Grey: Young ice 10-15 cm thick. Less elastic than nilas and breaks on swell. Usually rafts under pressure.
Grey-white: Young ice 15-30 cm thick. Under pressure it is more likely to ridge than to raft.
Thin first-year: First-year ice of not more than one winter's growth, 30-70 cm thick.
Medium first-year: First-year, ice 70-120 cm thick.
Thick first-year: First-year ice over 120 cm thick.
Old ice: Sea ice which has survived at least one summer's melt. Topographic features generally are smoother than first-year ice. May be subdivided into second-year ice and multi-year ice.
Second-year ice: Old ice which has survived only one summer's melt.
Multi-year ice: Old ice which has survived at least two summer's melt.
Lake-ice types
New: Recently formed ice less than 5 cm thick.
Thin: Ice of varying colours, 5-15 cm thick.
Medium: A further development of floes or fast ice, 15-30 cm thick.
Thick: Ice 30-70 cm thick.
Very Thick: Floes or fast ice developed to more than 70 cm thickness.
Arrangement of the ice
Ice drift: Caused by the combined action of the wind and water current's drag on the ice. Expressed in units of kilometres per day (km/d). Terms used are descriptive: slow or light, moderate, rapid, and variable.
Ice growth: Caused by the freezing of water by cold air, and its rate will depend on the air temperature, wind conditions, and water salinity. Terms used are descriptive: little or no ice growth, slow or light, moderate, and rapid.
Ice melt: Caused by the melting of ice by warm water or warm air. Terms used are descriptive: slow or light, moderate, and rapid.
Ice pressure: Caused by compaction of ice floes under the influence of wind or water currents, forming ice deformation of several forms (fractures, hummocks, ridges, rafting). Terms used are descriptive: light, moderate, strong. |
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Category : climate
| Posted By : Gareth |  Comments[138] |  Trackbacks [0] |
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| 30 Apr 2008 04:04:44 pm |
| On the formation of Sea Ice.. |
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- Excerpt from Ms Smilla's Feeling for Snow, Peter Hoeg, 1993 (Pg 450).
The Ice cover was formed last year in the Arctic Ocean. From there it was forced out between Svalbard and the east coast of Greenland, carried down around Cape Farewell, and pushed up along the west coast.
It was created in beauty. On an October day the temperature drop 30 degrees in 4 hours, and the sea grows as motionless as a mirror. Its waiting to reflect a wonder of creation. The clouds and the sea now glide together in a curtain of heavy grey silk. The water grows viscous and tinged with pink, like a liquor of wild berries. A blue fog of frost smoke detaches itself from the surface of the water and drifts across the surface of the mirror. Then the water solidifies. Out of the dark sea the cold now pulls up a rose garden, a white blanket of ice blossoms formed form salt and frozen drops of water. They may last for four hours or two days.
At his point the structure of the ice crystals is based on the number 6. Surrounding a hexagon, like a honeycomb of solidified water, six arms reach out towards six other cells, which in turn – as seen in a photograph taken with a colour filter and greatly enlarged – dissolve into new hexagons.
Then frazil ice is formed, grease ice, and pancake ice, whose plates freeze together in floes. The ice separates out the salt, the seawater freezes from below. The ice breaks, packing, precipitation and increased cold give it an undulating surface. Eventually the ice is forced adrift.
Frazil ice
Grease ice
Pancake ice |
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Category : climate
| Posted By : Gareth | Comments[109] | Trackbacks [0] |
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| 30 Apr 2008 03:00:24 pm |
| 12 hour disassembly |
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Jakkelsen is leaning against the rail. “this is incredible, fucking incredible!”
The complex below us is lit up with lights on poles lining both sides of the piers. Even now, bathed in this yellow light, painted grass green, with lights on in the distant buildings, and white traffic markings, Greenland Star looks like some thousands of square metres of steel plunked down in the Atlantic Ocean.
To me it seems so obviously a mistake. To Jakkelsen it’s a magnificent union of sea and high technology.
“Yes”, I say “ and the best thing is it can be taken apart and packed up in 12 hours”.
“With this place they have won over the sea, man. Now it doesn’t matter how, or what the weather’s like. They can put down a harbour anywhere, in the middle of the ocean”.
I’m no teacher or Boy Scout leader. I’m not interested in setting him straight.
“Why do they need to take it apart, Smilla?”
Maybe its nervousness that makes me answer him after all.
“They built it when they started bringing up oil from the sea floor off North Greenland. It took ten years from the time they first discovered oil until they could extract it. Their problem was the ice. First they built a prototype of what was to be the world’s largest and most solid oilrig, the Joint Venture Warrior, a product of Glasnost and Home Rule, a cooperative venture between the United States, the USSR, and A.P. Moller Shipping Inc. You’ve sailed past oil rigs, you know how big they are. You see them 50 sea miles away, and they get bigger and bigger, like a universe floating on posts. They’ve got restaurants, and offices and workshops and bars and cinemas and theatres and fire stations, the whole thing mounted 12 metres above the surface of the ocean so even the worst storm waves pass underneath it. Just think of one of them. The Joint Venture Warrior was meant to be 4 times as big. The prototype was 18 metres above the surface of the water. It was intended to provide jobs for 1400 people. They erected the prototype in Baffin Bay. When it was standing there, finished, an ice berg came along. This had been foreseen. But this iceberg was a little bit bigger then usual. It was calved somewhere on the edge of the Arctic Ocean. It was a hundred metres tall and flat on the top, the way icebergs are when they are that high. It had 400 metres of ice below the surface, and it weighed about 20 million tons. When they saw it coming they did get just a little nervous. But they had two big icebreakers on hand. They fastened them to the ice berg so they could pull it on to a different course. There was very little current and no wind. Still, nothing really happened when they revved up the engines. Except that the ice berg continued straight ahead. It did not seem to notice that anything was tugging at it.And it walked right over the prototype, and behind it, in the water, there was no traces of the proud model of the Joint Venture Warrior except for some patches of oil and debris. Since then they have made all Arctic Ocean equipment so it can be dismantled in 12 hours. That’s how much warning the Ice Centre can give them. They drill from floating platforms that can scarper. This magnificent harbour is nothing more then a tin tray. If the ice came along it would carry it off as if it had never been here. They only put it up during mild winters when the ice field doesn’t reach this far north or the pack ice this far south. They haven’t beaten the ice, Jakkelsen. The battle hasn’t even begun.”
He puts out his cigarette. He has his back to me. I don’t know whether he’s disappointed or indifferent.
- Excerpt from Ms Smilla's Feeling for Snow, Peter Hoeg, 1993 |
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Category : climate
| Posted By : Gareth | Comments[82] | Trackbacks [0] |
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| 07 Apr 2008 11:05:06 pm |
| Sunday Times, March 23rd |
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Category : climate
| Posted By : Elaine | Comments[51] | Trackbacks [0] |
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| 07 Apr 2008 12:04:22 pm |
| Sunpath: Carrick on Shannon |
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www.gaisma.com offers sunrise, sunset, dawn and dusk times around the world.
Sun path diagram (also known as "solar path diagram", "sun chart" or "solar chart") is a visualization of the sun's path through the sky. This path is formed by plotting azimuth (left-right) and elevation (up-down) angles of the sun in a given day to a diagram.
To find out the position azimuth = 60, elevation = 30, for example, imagine standing at the center of the diagram heading to the true north. To find the azimuth angle 60, you must turn 60 degrees to the right. Now the altitude angle 30 can be located by raising your head 30 degrees from the horizon.
SUNPATH DIAGRAM FOR CARRICK ON SHANNON
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Category : climate
| Posted By : Elaine | Comments[31] | Trackbacks [0] |
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| 28 Mar 2008 03:26:05 pm |
| Ice & Time |
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Jacobshavn Glacier retreat: The rapidly retreating Jakobshavn Glacier in western Greenland drains the central ice sheet. This image shows the glacier in 2001, flowing from upper right to lower left. Terminus locations before 2001 were determined by surveys and more recent contours were derived from Landsat data. The more recent retreat lines indicated in this image are longer than the earlier ones, and the increasing area of retreat suggests the possibility of increasing glacier acceleration as more ice flows into the fjord. Ice flowing into the fjord, however, would still have to pass through the same bottleneck of rock. NASA image by Cindy Starr, based on data from Ole Bennike and Anker Weidick (Geological Survey of Denmark and Greenland) and Landsat data.
Reference: http://nsidc.org/sotc/iceshelves.html |
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Category : climate
| Posted By : Gareth | Comments[49] | Trackbacks [0] |
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| 28 Mar 2008 03:04:15 pm |
| Breaking News - Wilkin's Ice Sheet |
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The Wilkins Ice Shelf is a broad plate of permanent floating ice on the southwest Antarctic Peninsula, about 1,000 miles south of South America. In the past 50 years, the western Antarctic Peninsula has experienced the biggest temperature increase on Earth, rising by 0.5 degree Celsius (0.9 degree Fahrenheit) per decade. NSIDC Lead Scientist Ted Scambos, who first spotted the disintegration in March, said, "We believe the Wilkins has been in place for at least a few hundred years. But warm air and exposure to ocean waves are causing a break-up."
The area that has broken off is roughly the size of Conneticut in the United States. The last major break off was the Larsen B Ice sheet in 2002. Scientists were shocked when its 500 billion tonnes of ice sheet disintegrated in less than a month.
Antarctic Ice Shelf Disintegration Underscores a Warming World :
http://nsidc.org/news/press/20080325_Wilkins.html from the National Snow and Ice Data Center (NSIDC),
News report: http://www.youtube.com/watch?v=8v55T_BhmlA
Animation of the Wilkins disintegration (February 28—March 17) from the NSIDC
http://nsidc.org/news/images/20080325_wilkins_animation_low.mov |
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Category : climate
| Posted By : Gareth | Comments[53] | Trackbacks [0] |
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| 25 Mar 2008 05:30:10 pm |
| 2 Suspect Icebergs |
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Above: a scanned copy of the photographic print of the iceberg with which the RMS TITANIC supposedly collided with April 14, 1912 at latitude 41-46N, longitude 50-14W.
This print was in possession of Captain De Carteret, the Captain of the Cable ship MINIA, reportedly stated that this was the only iceberg near the scene of the collision. The MINIA was one of the first ships to reach the scene following the disaster. During the rescue operation, the MINIA found debris and bodies floating in the vicinity of the above iceberg. Therefore, it is assumed that this is the iceberg that the TITANIC struck.
Above: Another iceberg was photographed by the chief steward of the liner Prinze Adelbert on the morning of April 15, 1912, just a few miles south of where the Titanic went down. The steward hadn't yet heard about the Titanic. What caught his attention was the smear of red paint along the base of the berg, indication that it had collided with a ship sometime in the previous twelve hours. Other accounts indicated that there were several icebergs in the vicinity where the TITANIC collided.
Which ever Iceberg was responsible I find it interesting that within 3 weeks of the disaster they would have melted into almost nothing in the surrounding ocean as the Gulf stream pulled them south towards warmer climes. Thus, they were gone, their only legacy being a savage blow dealt to the optimism of the industrial age. I am interested by the unusual contrast of the epic with the ephermal manifested by these behemoths.
The International Ice Patrol was established to monitor the seasonal movement of glaciers after the titanic disaster: www.uscg.mil/lantarea/iip/FAQ/Titanic_1.shtml |
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Category : climate
| Posted By : Gareth | Comments[45] | Trackbacks [0] |
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| 14 Feb 2008 02:17:21 pm |
| Environmental time vs human memory... |
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An 1870 postcard view of the Rhone glacier in Gletsch, Switzerland, contrasted dramatically with the shrinking 21st-century version of it. Ironically 'gletsch' is the German for glacier.
Image from http://firstpulseprojects.net/Strange-Weather-mt/05-disasters/ With article from New York Times http://www.nytimes.com/2006/10/24/world/europe/24swiss.html?ex=1319342400&en=e5799377c890c8e8&ei=5090&partner=rssuserland&emc=rss
'People often fail to connect emotionally with changes that are too slow to observe...' - James Labinski, Sound Artist |
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Category : climate
| Posted By : Gareth | Comments[68] | Trackbacks [0] |
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