BLOGGER'S NOTE, August 10: for a new set of graphics that give much more detailed information, go to the bottom of this particular post.
BE SURE TO CLICK ON THE IMAGES TO ENLARGE THE DETAIL.
From Polar View at the Technical University of Denmark (http://www.seaice.dk/):
BELOW: Graphic from August 10, 2008:
From the Cryosphere Today site (run by the Universities of Illinois and Colorado), a comparison of the Arctic on August 9 and July 22, 2007 and 2008:
Go to this link and put in dates for comparison -- the most recent day is usually available before the evening: http://igloo.atmos.uiuc.edu/cgi-bin/test/print.sh
The graphics below are from NOAA of global sea surface temperature anomalies on August 7 and July 24, 2008.
Link to updated graphics: http://www.osdpd.noaa.gov/PSB/EPS/SST/climo.html
The image below is a NOAA graphic of the 500-hPa height anomalies in the Northern Hemisphere on June 9, 2008. Click on the link below the graphic to see the most recent 30-day animation.
Link to past 30-days' animation: http://www.cpc.noaa.gov/products/intraseasonal/z500_nh_anim.shtml
BELOW: from Bremen University, a graphic of the Arctic Sea Ice extent, on August 10, 2008 (be sure to click on it in order to see the detail):
Link to the graphics above (occasionally data are missing and are represented by grey areas -- normally, these areas will be filled in by the morning of the following day): http://www.iup.uni-bremen.de:8084/amsr/amsre.html
ABOVE: visual ice cover, August 10, 2008.
BELOW: July 24, 2008 (from Bremen University).
Link to updated images: http://www.iup.uni-bremen.de:8084/amsr/arctic_AMSRE_visual.png
Link to photos (NOTE: to see photos from other days from 2008, change the 222 to the number of the day that you want, e.g., 222 is August 9th, and 208 is July 26th, and so forth): http://manati.orbit.nesdis.noaa.gov/ice_image21/D08222.NHEAVEH.GIF
BELOW: from the Japanese Aerospace Exploration Agency, a graphic of Arctic Sea ice extent for the current and past years, August 9, 2008. The latest value : 6,417,656 km2:
Link to graphic: http://www.ijis.iarc.uaf.edu/en/home/seaice_extent.htm
BELOW: National Snow and Ice Data Center graph of Arctic Sea ice extent, August 10, 2008:
Link to graph: http://nsidc.org/data/seaice_index/images/daily_images/N_timeseries.png
I find the image below fascinating (and it is the scariest of all):
Link to updated TLT channel temperature anomalies graph (NOTE: often due to volume of traffic it is not possible to access the link -- try again later):
http://www.remss.com/msu/msu_data_description.html#figures
And, below, find an animation of global surface temperature anomalies for the past 30 days -- most disturbing are the anomalies occurring at Antarctica many of which are much higher than 20 C.
Link to animation above: http://www.cdc.noaa.gov/map/images/fnl/sfctmpmer_01a_30frames.fnl.anim.html
ABOVE: image from August 4th, 2008.
BELOW, temperature map of the Arctic (first click on the link below the picture, then click on the yellow dots to see weather conditions -- some dots are inactive):
Link to map: http://www.athropolis.com/map2.htm
BELOW: graphic of ice thickness (http://seaice.bplaced.net/gfs.html):
BELOW: graphic of 2-meter height temperatures (http://seaice.bplaced.net/gfs.html):
Hello Tenney Naumer,
ReplyDeleteCobblyWorlds here, at RC you posted:
The mechanics of heat exchange or whatever it is called are unknown to me. I don’t understand what is going on when the ice freezes or when it melts, and how that works in the Arctic. I just know that I saw a lot of vapor rising, which in my ignorance means that the water below the ice was warmer than the air above it. In my mind, an absolutely incredible amount of heat left the water (from April through June) and went into the air, and at some point, a type of equilibrium was reached after which very little vapor was created.
Apologies for the length, but I'm assuming from your question that it's best to proceed as if you know none of the physics. And it's complex although I have tried to keep it plain english.
So here goes:
When the ice forms a skin of ice forms over the surface, as this congeals it gradually forms thicker ice, obviously it can't freeze from above so the freezing must happen on the underside. For the water to freeze to the underside of the ice there has to be a movement of heat from the sea, through the ice, to the surface.
The heat transfer through unbroken ice is inversely proportional to the thickness of the ice. To show what I mean by "inversely proportional" consider doubling, 2, 4, 8, 16, 32, etc. "Inversely proportional" means it's 1/2, 1/4, 1/8, 1/16, 1/32 etc, see how those numbers dwindle to very small numbers very fast. 2 doublings of thickness takes you from half the heat transfer to an eighth the heat transfer.
So as the ice gets thicker there's a massive reduction in the amount of heat that can get to the surface, and as this removal of heat is what causes freezing to the underside of the ice, that slows the rate of freeze.
Initially the ice formed is thin, as it grows thicker it thickens more slowly. This is why you get such a massive initial spreading out of ice.
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The surface is cooled not only because sunlight is reflected, but also because the ice acts as an insulating "lid" over the ocean. Indeed in winter when there is no sunlight, reflecting ligh is not an issue. The Poles are a unique environment and it's probably best considering a more normal day/night cycle.
Take a typical day, sometime after midday you typically get the highest temperatures after the sun has had a chance to pour energy in to ground and warm things up. As the sun gets lower in the evening things cool down. That's because there's a continual "battle" between heat going out into the atmosphere (and ultimately into space), and heat from incoming sunlight. Once the incoming sunlight reduces enough the heat loss overcomes the sun's warming and things cool. Then through the night there's no incoming sunlight so things cool further until typically shortly before dawn when you get to the minimum temperature.
In the Arctic this day/night cycle is spread over 12 months. The sun rises after March (dawn) and it's in March that the ice-cap is at it's greatest extent. The sun sets after September, and it's then that the ice-cap is at it's minimum extent due to the warming throughout the Arctic "day" (spring/summer).
Heat fluxes in the atmosphere from lower (warmer) lattitudes play a role, but simply speaking: In winter the Arctic is losing heat to space, in summer it's gaining heat from the sun.
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The ice insulates the ocean, so even in the depths of winter it doesn't freeze all the way down to the deeps. It also stops the air being warmed much by the ocean. However where it breaks open the exposed ocean can pump huge amounts of energy into the atmosphere, fluxes of as much as 1000 watts per square metre have been measured! The ocean is only a few degrees above freezing, but the atmosphere can be colder than -20degC. It's this difference in temperature that drives the heat transfer, the bigger the difference the greater the rate of heat transfer.
It takes a lot of heat to evaporate water, and as energy can't be created or destroyed (you can only change it's form), that heat counts as heat delivered into the atmopshere. When the vapour cools and condenses as it hits the atmosphere it delivers back the heat it took to evaporate. That heat stored in water vapour is called "latent heat".
The heat in water vapour also feeds storms leading to an increase in storminess (will explain if asked). The Circum Polar Flaw Lead team noted that last year areas of the Beaufort Sea were kept open until December by open water delivering heat and water vapour into the atmosphere.
So yes, where the ice breaks you can get locally ferocious deliveries of heat into the atmopshere, and as the atmosphere is very cold, you get instant clouds/fog. This hides the sort of features we'd like to see. However as there is no incoming sunlight, eventually the loss of heat to space cools the region to such a degree that the freezing wins out. The Arctic atmosphere becomes so cold it is very dry. This is why QuikScat and the satellite infra-red images are only really useful in the winter. It's also why there's much less cloud. As things warm up into the summer water vapour levels rise and it gets cloudier.
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QuikScat is essentially a radar system that uses a frequency that is reflected by water molecules, it shows the difference between perennial (white) and first year ice (grey) because of salt/brine inclusion in the ice. As the ice ages the salt/brine leaks out.
The infra-red images see what is in effect greenhouse emission (the same sort of infra-red(IR) involved in the Greenhouse Effect). The IR images are produced as negatives - white is colder(darker) black is warmer (brighter) - darker/brighter refers to the IR brightness.
This last winter I used QuikScat/IR/AMSRE combined to take advantage of the different things they show. You will see real cracks of a smaller size on the IR than QuikScat because the ice isn't emitting that wavelength of IR, but the fissures do, so the fissures show up black. Also QuikScat has a lower resolution than the IR images and is averaged over 24 hours.
Any questions welcome, hope this doesn't lose you.
Cobbly.
Dear CobblyWorlds,
ReplyDeleteThank you so much for the explanation and no you didn't lose me and I have a few questions regarding heat exchange when the sea ice freezes and thaws, but first I need to finish updating this post, and my connection is slow this afternoon.
More later, and thanks again,
Dear CobblyWorlds,
ReplyDeleteI will have to write the questions tomorrow or the day after because tonight I have to compose a letter to the IRS for my daughter. So, more later, but I really do have some questions about heat exchange between freezing and melting ice and air and water, so I will write more when I get a chance. Best, Tenney
"BLOGGER'S NOTE, August 11: vast stretches of the Arctic Sea ice are quite thin -- in the range of 10-20 cm only.."
ReplyDeleteHow do we know this? Any ice thickness data published somewhere?
Dear B Buckner,
ReplyDeleteHave a close look at the second to last graphic and the scale.