Ave max deviation is 1,234.554km2 and occurs on 09 September. The period from 22 Aug to 18 Oct has an average deviation in excess of 1,000,000km2.
<<2. The lowest deviation from the monthly average appears to be the spring - Mar/Apr/May>>
Aver min deviation is 308,966km2 and occurs on 25 May. The period from 09 Apr to 21 June has an average deviation less than 500,000km2.
<<3. 2007 had a large spring deviation and is the second lowest minimum.>>
Ave sea-ice extent for each day in Spring 2007 was 12,896,975km2, the mean being 13,160,875km2
<<4. 2012 was within the monthly average in the spring yet reached a new record minimum.>>
From 23 Feb to 07 June the sea-ice extent was at or above average in recent years. On 14 and 16 April it reached the highest for more than 10 years. From 08 June it retreated rapidly reaching a record low on 24 Aug and continued receding until 16 Sep when extent was 3,489,063km2.
<<5. With the exception of 2009, the summer melt in Jun/Jul seems to be tightly grouped (e.g. unlike the minimums which are fairly spread apart.)>>
Not sure what you’re saying, the summer melt in June and July 2009 was pretty typical for recent years.
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The reason why the March maxima are more closely bunched together then the September minima is a consequence of Arctic weather conditions and the way that Arctic sea-ice extent is measured.
The way that sea-ice extent is calculated is by determining the amount of ice present in each cell of a grid overlaid onto the ice, this is at a 25km resolution. If a data-cell has more than 15% ice cover then it is assigned a value of 1, if there is no ice or less than 15% then the value is 0. Thus it’s defined as a simple binary term. The number of cells with a value of 1 then determines the extent of the sea-ice.
During the cold winter months the sea freezes solid into a more solid single mass. As the weather warms the ice begins to break apart, wind and ocean currents carry the broken pieces of ice away from the central mass of ice.
Because the ice is more clumped into one solid block during winter there is less variation in the extent of the sea-ice. As the ice breaks up it can start drifting, the more it breaks apart and the further it drifts the greater the potential for a significant difference between the minimum values.
It’s not so much that the Arctic was particularly hot last year that melted so much ice, more due to unusual wind patterns. In 2012 there were a series of Arctic Dipole Anomalies in which the normal weather patterns in the Arctic went into reverse, this meant that ice was blown away from the central mass and into warmer waters where it melted.
<< (And just for fun, make a prediction for this year's minimum. Mine is exactly 4M km2 for fifth lowest.) >>
It’s a hard one to predict as there’s a lot of uncertainties. At the moment there’s nothing to suggest that anything particularly unusual will happen, but then that was the case a year ago and we ended up with a record breaking minimum. I’m going to be a bit more optimistic and go for 4,688,916km2, and I’ll go so far as to predict the minimum will occur on 17 September.
The most important is the minimum as it represents the dense, old ice. The maximums are the results of the current year freeze. As your data is 'extent' rather than volume, the maximums are effected each year by winds and/or currents which can thin and spread the new seasonal ice.
If you look at volume, you see very little seasonal deviation from the ongoing rate of decline.
http://arctic-roos.org/observations/sate...
http://thinkprogress.org/climate/2011/05...
Thickness is declining
http://psc.apl.washington.edu/wordpress/...
I don't see the importance of ice extent for tracking climate change as is it a function of wind spreading the ice out. It may be important for predicting weather for the upcoming year, given the affect of arctic ice on the jet stream. But for tracking ongoing changes of the environment, it is the volume to watch.
It's as much to do with wind direction and strength as it is to do with temperature, 2012 had an unusually violent and long lasting storm, not all the ice was lost, some was blown on top of other ice, which was shown by the rapid refreeze.
My guess is 4.2 km similar to 2010.
Weather
Here in Relativistic Denial-Land, the answer to this question obeys the Yahooian Uncertainty Principle:
It depends on standpoint of the observer.
http://www.skepticalscience.com/pics/1_A...
Please have a look at the latest graphic for Arctic sea ice extent which covers 2007 to present: http://arctic-roos.org/observations/satellite-data/sea-ice/observation_images/ssmi1_ice_area.png
I've noted some interesting features of this graphic as follows:
1. The greatest deviation from the monthly average seems to be right at the yearly minimum around early September.
2. The lowest deviation from the monthly average appears to be the spring - Mar/Apr/May
3. 2007 had a large spring deviation and is the second lowest minimum.
4. 2012 was within the monthly average in the spring yet reached a new record minimum.
5. With the exception of 2009, the summer melt in Jun/Jul seems to be tightly grouped (e.g. unlike the minimums which are fairly spread apart.)
So like I mention in my subject question, what could be the physical reasons for these observation?
(And just for fun, make a prediction for this year's minimum. Mine is exactly 4M km2 for fifth lowest.)
