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Neven, nice overview!
Commented Jul 27, 2012 on Arctic atmosphere June-July 2012 at Arctic Sea Ice
Crandles, thank you! You wrote: "Area is either 34km^2 as you said or more likely there is an extra wrinkle not explained that says concentration under 15% isn't counted for area making the answer 16km^2. Extent is 100km^2 (one cell of over 15%)" => Yes, I think you're right that the extra wrinkle not explained is that concentration under 15% isn't counted for area (and extent)making. That indeed (probably) the correct answer is: Extent is 100km^2 (one cell of over 15%)(and area is 16 km^2). Your example how you think NSIDC and IJIS calculate extent and area makes sense to me! Thank you.
I found three definitions of Sea ice area and Sea ice extent on the internet: 1) Definition on Wiki: To estimate ice area, scientists calculate the percentage of sea ice in each pixel, multiply by the pixel area, and total the amounts. To estimate ice extent, scientists set a threshold percentage, and count every pixel meeting or exceeding that threshold as “ice-covered.” The National Snow and Ice Data Center, one of NASA’s Distributed Active Archive Centers, monitors sea ice extent using a threshold of 15 percent/ 2) Definition on ijis website: The area of sea-ice cover is often defined in two ways, i.e., sea-ice "extent" and sea-ice "area." These multiple definitions of sea-ice cover may sometimes confuse data users. The former is defined as the areal sum of sea ice covering the ocean (sea ice + open ocean), whereas the latter "area" definition counts only sea ice covering a fraction of the ocean (sea ice only). Thus, the sea-ice extent is always larger than the sea-ice area. Because of the possible errors in SIC mentioned above, satellite-derived sea-ice concentration can be underestimated, particularly in summer. In such a case, the sea-ice area is more susceptible to errors than the sea-ice extent. T hus, we adopt the definition of sea-ice extent to monitor the variation of the Arctic sea ice on this site. 3) Definition on NSIDC website: Extent is different from the total area in that if a given region has a percentage of ice concentration greater than the threshold, the entire region is considered "ice-covered." Total area tells how much of the region is actually covered by ice. Arctic- or antarctic-wide sea ice extent is always a larger number than area. My interpretation of the above is as follows: E.g. you have 3 pixels (3 squares). Each pixel (square) has a surface of e.g. 100 km2. Assume (the surface of) square 1 is ice covered for 8% Assume (the surface of) square 2 is ice covered for 10% Assume (the surface of) square 2 is ice covered for 16% Then, based on the above definitions: the total 15% ice extent for the three squares would be: 8 km2 (below threshold of 15%) + 10 km2 (below threshold of 15%) + 100 km2 = 118 km2 the total ice area for the three squares would be: 8 km2 + 10 km2 + 16 km2 = 34 km2 Is the above interpretation of the definitions correct or am I missing something?
Neven, very nice overview! According to GFS in about a few days the weather will turn significantly cooler in large parts of the Chuckchi Sea and the East Siberian Sea. Seen whether this will restrict the speed at which the ice melts there. (Assuming the weather will become cooler).
Commented Jul 9, 2012 on Stronghold at Arctic Sea Ice
Neven, Again a nice overview!
Commented Jul 3, 2012 on Fringe fries part 2 at Arctic Sea Ice
@Pete, part 2 of my possible BS speculations... Some speculation about mondial factors … On a yearly basis the tropical and subtropical zones receives much more energy than the ‘other’ zones. Out of my head some so called experts ( I have no link available at this moment) suggests that an increase (or decrease)in the temperature in the tropics will lead with some lag in time to resp. an increase (or decrease) in the temperature in the more northerly and southerly regions and not (or much less) the other way around. Very warm (tropical) air saturated with water vapor contains much more latent heat than colder air saturated with water vapor. In the tropical zone there is much more very warm air saturated with water vapor than it is the case in the other (not tropical zone) parts of this world. If I am correct, when 1 m3 of very warm air of e.g. 27 degrees Celsius ‘saturated with water vapor’ cools down 1 degree (e.g during a La Nina), the amount of water vapour that condensates is about 1,39 gram (in this case the amount of about 1,39 x 2256 Joule of energy is released during the condensation). A part of this energy (warmth) is transported outside the tropical zone to more northerly and southerly areas. When 1 m3 of cooler air of e.g 5 degrees Celsius ‘satured with water vapor’ cools down 1 degree, the amount of water vapour that condensates is about 0,45 gram (in this case the amount of about 0,45 x 2256 Joule of energy is released during the condensation). So, temperature is not 1 to 1 to the amount of energy. General speaking, it cost less energy to warm cold air 1 degree than warm air. Also acording to so called experts, ocean currents transport energy from one place to other places. The suspicion is that it takes many years before the effects of a warming or cooling tropical zone is manifested in the very northern latitudes. Not talking about the very complicated dynamics of clouds. All combined (mondial and local factors) creates in my view a very dynamic and complicated proces.
Commented May 13, 2012 on PIOMAS May 2012 at Arctic Sea Ice
@Pete, Nice point. Maybe the story below is also uninformed BS. I am not sure but maybe the main focus on this blog is more on ‘local factors on the northpole’ and much less on mondial factors, although I read something about e.g. the possible effect of the influx of warmer Atlantic water into the arctic ice. Some specalion about possible ‘build up inertia’ to cooling effects in the Northpole region: Maybe, like you suggest, the north pole is lagging behind the tropics partly because the northpole region has ‘build up inertia’ to cooling effects because of its weather history (a lot of melted ice because of the relative warm history). The build up inertia has an effect on the local wheather in the Northpole region. That because of e.g. less ice cover (and other related factors) there is less sustained colder weather in the Northpole regio. A lot of sea ice has disappeared with a strong effect on the summer albedo. To compensate for the build up inertia due to e.g. the lost ice and warmer water (and other related factors), a period with sustained colder weather is needed to significantly increase the amount of northpole ice. But when there is suddenly a longer period with sustained colder weather in large parts of the northpole region, your suggestion that the amount of see ice will increase very fast will in my opinion be very true.
Commented May 13, 2012 on PIOMAS May 2012 at Arctic Sea Ice
Neven, great blog! I am just an uninitiated one about the arctic sea ice subject. You said: "clouds keep things warmer 'right now' by blocking out-going radiation..." I thought that from the beginning of May till the middle of august arctic cloud in general has a net negative effect on the temperature, but ofcourse i could be wrong. Or is the negative effect of arctic cloud general speaking only in the June /July period? E.g.: http://nsidc.org/arcticmet/patterns/feedback_loops.html "=>Except in summer<=, arctic clouds seem to have a warming effect. This is because the blanket effect of clouds tends to dominate over reductions in shortwave radiation to the surface caused by the high cloud albedo". and "The 2011 wintertime increase and => summertime decrease in cloud amount resulted in greater downward energy flux and surface warming <=, potentially contributing to the near record low sea ice extent this year (see the essay onSea Ice). This is in contrast to the general trend over the period 1982-2004, when a decrease in wintertime clouds and increase in springtime clouds over parts of the Arctic acted to dampen surface warming (Wang and Key, 2003,2005)".
Commented May 13, 2012 on ASI 2012 update 2: no daily data at Arctic Sea Ice
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