|
Post by itocalc on Apr 2, 2009 1:47:02 GMT
Although I do not understand it, polar explorers often very low body temperatures that would kill in ordinary circumstances. Ernest Shakleton reports body temps so low that the thermometers registered nothing. Then after eating sugar cubes they would get a reading for a few minutes before going below range again. I think the report comes from 1908.
Also, in 1913 there were 92 consecutive spotless days. Shakleton's Endurance expedition to antarctica was stopped by excessive sea ice in December 1913 and January 1914. So we must wait until December to see if the pattern of 1913 is repeated.
|
|
tsh
Level 2 Rank
Posts: 69
|
Post by tsh on Apr 2, 2009 11:45:03 GMT
Although I do not understand it, polar explorers often very low body temperatures that would kill in ordinary circumstances. Ernest Shakleton reports body temps so low that the thermometers registered nothing. Then after eating sugar cubes they would get a reading for a few minutes before going below range again. From what I understand, the thermometers used for a long time had a minimum of about 34 centigrade, 28 degrees is generally survivable, and 24 is generally terminal (given intensive care facilities). The lack of range in the readings is one reason for generally very poor data on severe hyopthermia. Read 'Essentials of Sea Survival' By: Frank Golden, Michael Tipton if you're interested in more (or if you spend any time on the water)
|
|
|
Post by gridley on Apr 2, 2009 15:49:05 GMT
Also bear in mind that ice can only form if there is water available, regardless of the temperature. In other words, the ice pack will only grow if snow or rain is falling on it, or if the edges in contact with water are below freezing (all else being equal). Having -45C in an area with no liquid doesn't do a thing to increase ice coverage. thanks, ron. i think many lay people like me see declining ice extent and assume melting ice. Even in a big ocean it seems counter intuitive that with it -45C in some portion of the arctic, it could be above 0C elsewhere. (I assume ocean ice melts at about 0C) Even so, new ice should still be forming where it's way below freezing. Wind compacting the ice makes some sense as well, although one would expect that to happen in the dead of winter as well. by the way, if that Catlin guy's body temp is accurate at 34.19C, someone needs to start treating him for hypothermia. He could be in serious trouble, and is probably jhaving difficulty functioning.
|
|
|
Post by Belushi TD on Apr 2, 2009 21:38:24 GMT
Gridley - not quite....
Heat flows from a warmer location to a colder location. Admittedly, the thermal conductivity of ice is pretty low, but you still get heat conducted from the water under the ice through the ice to the air above the ice. This happens when the air is colder than the ice.
Depending on how far into it you want to delve, you can see all kinds of spiffy things when you take thermodynamics a long way. I've almost no comprehension of it, aside from what I picked up as a geologist looking at permafrost. Permafrost melts from the bottom up AND the top down. It only freezes from the top down as the heat is transferred to the atmosphere. Same thing with sea ice.
Belushi TD
|
|
|
Post by ron on Apr 3, 2009 1:44:55 GMT
Except this is ice extent and it is a measurement of the area of the oceanic surface that is covered by 15% or more of ice, irrespective of the thickness.
|
|
|
Post by ron on Apr 4, 2009 14:34:11 GMT
Well, I sent an email to caitlin about their live data feeds -- I didn't get a response. So I sent a follow up email yesterday.
Whataya know? They removed the live ice thickness feed from the page completely, but they did turn on the live bio telemetry feed.
www.catlinarcticsurvey.com/live_from_the_ice.aspx
Who was it that predicted this first? Well, whadaya know? I got a response this morning: Strange file? Maybe the one where they said "Oh, let's get the bio feed running, remove the ice data feed, then file this email?" file? Anyway, I guess someone is reading the email, even if it takes 9 days to do it. They're busy with people on the ice!
|
|
|
Post by jimg on Apr 4, 2009 20:30:58 GMT
Belushi:
You touched on something I have been wondering about.
What is graph of ice thickness vs delta-T.
At some point of ice thickness, the heat being removed from the ocean will match the heat removed from the ice and you'll have steady state heat transfer and a maximum ice thickness for a given temp.
Though I haven't been able to get to it yet.
|
|
|
Post by kiwistonewall on Apr 4, 2009 21:29:55 GMT
Belushi: You touched on something I have been wondering about. What is graph of ice thickness vs delta-T. At some point of ice thickness, the heat being removed from the ocean will match the heat removed from the ice and you'll have steady state heat transfer and a maximum ice thickness for a given temp. Though I haven't been able to get to it yet. The system is far to dynamic for that: 1. Depth and composition of Snow cover on top of ice. 2. Water temperature below ice - depends on nature of ice above. 3. Salinity of water below ice. 4. Density (entrapped air) and salinity of ice both vary with age, and with the speed that the ice initially formed, 5. Wind speed 6. ocean current. 7. Depth of ice. There are attempts at modelling the process, but simply too many variables for "ice thickness vs delta-T." Latest ice:
|
|
|
Post by jimg on Apr 5, 2009 3:44:47 GMT
If the upper surface of the ocean is about 4 degrees, then there is an upper bound on T_hot.
The specific heat capacity for ice is a constant.
Now you're left with area and T_cold.
There will be some value of d, thickness, for which equilibrium is met.
Wind and water motion will increase the rate of freezing, but they won't decrease it, (unless warmer water is introduced). Since it heat transfer in/out of a fluid does involve the mass flowrate.
However, heat transfer through an insulator at the boundary layers will have some thickness whereas to freeze another millimeter of ice in thickness will take days.
|
|
|
Post by kiwistonewall on Apr 6, 2009 11:16:06 GMT
|
|
|
Post by kiwistonewall on Apr 6, 2009 20:53:02 GMT
|
|
|
Post by tobyglyn on Apr 6, 2009 22:29:51 GMT
Oh dear.... "ScienceDaily (Apr. 6, 2009) — The latest data from NASA and the University of Colorado at Boulder's National Snow and Ice Data Center show the continuation of a decade-long trend of shrinking sea ice extent in the Arctic, including new evidence for thinning ice as well. The researchers, who have been tracking Arctic sea ice cover with satellites since 1979, found that the winter of 2008-09 was the fifth lowest maximum ice extent on record. The six lowest maximum events in the satellite record have all occurred in the past six years, according to CU-Boulder researcher Walt Meier of NSIDC. The new measurements by CU-Boulder's NSIDC show the maximum sea ice extent for 2008-09 reached on Feb. 28 was 5.85 million square miles, which is 278,000 square miles below the average extent for 1979 to 2000, an area slightly larger than the state of Texas, said Meier. In addition, a team of CU-Boulder researchers led by Research Associate Charles Fowler of the Colorado Center for Astrodynamics Research, or CCAR, has found that younger, thinner ice has replaced older, thicker ice as the dominant type over the past five years, making it more prone to summer melt. "Ice extent is an important measure of the health of the Arctic, but it only gives us a two dimensional view of the ice cover," said Meier. "Thickness is important, especially in the winter, because it is the best overall indicator of the health of the ice cover. As the ice cover in the Arctic grows thinner, it becomes more vulnerable to summer melt." www.sciencedaily.com/releases/2009/04/090406132602.htm
|
|
|
Post by ron on Apr 6, 2009 22:31:51 GMT
You're just looking at weather.
|
|
|
Post by tobyglyn on Apr 6, 2009 22:48:51 GMT
It's incredible how they spin this stuff .... "AN ICE wall damming the endangered Wilkins ice shelf against the Antarctic Peninsula has shattered, just as scientific alarms ring out about the region's rapid warming. The 40 kilometre-long bridge held for more than a year while ice behind it broke up, but European Space Agency images show it finally failed on Sunday night, and Australian glaciologist, Neal Young, said yesterday. "Now it looks like a laminated windscreen hit by a stone," said Dr Young, of the Antarctic Climate and Ecosystems Co-operative Research Centre in Hobart. The loss opens the way for thousands of square kilometres of ice behind it to float away. "All that mess will eventually be flushed out," Dr Young said. "If that clears, I would anticipate more fracturing around the Wilkins." An American scientist, Ted Scambos, has calculated about half of the 13,680 square kilometres comprising the Wilkins shelf is in danger of disappearing. It is the latest of seven great ice shelves afloat along the peninsula to collapse, and the furthest south. The warming is heading toward the globally important West Antarctic ice sheet." www.smh.com.au/environment/global-warming/fears-for-future-after-antarctic-dam-breaks-away-20090406-9uwm.html
|
|
|
Post by neilhamp on Apr 7, 2009 3:02:50 GMT
Most interesting post on Canadian Ice Kiwi
I see that the Canadian Ice Service state "Measurements are taken approximately at the same location every year on a weekly basis starting after freeze-up when the ice is safe to walk on, and continuing until break-up or when the ice becomes unsafe."
Not knowing much about ice in Canada I was surprised to find the ice thickens from December RIGHT THROUGH to "break-up" in May/ June each year. This doesn't seem to square with the Arctic ice extent which you also display for us. This seems to reach its maximum in March each year and then falls away as the Spring melt starts
The web site is not easy to navigate. They also state "The Original Ice Thickness Program has data collection which contains ice thickness and snow depth measurements for 195 sites going back as far as 1947 for the first established stations in the Canadian Arctic (Eureka and Resolute)"
I presume this is why you chose to show a graph of Resolute. They don't seem to graph their data on the site. Do you have graphs back to 1947?
|
|