Is it just me or does this year look much worse compared to 2012?
This model's been showing really unphysical stuff for the past weeks, dont trust it at any rate. 2015 is bad but not as much.
Every thickness model i have seen this year seems to be showing some very strange seemly impossible behaviour. Is it because they have new satellites are are still working out what the numbers really mean? or do we have a case that the ice is in such poor condition that the satellites can not tell what they are looking at?
Or could it be that the models are working fine but the 'ice' just doesn't have the mass we're used to, slush, crusty snow, rotten ice call it what you will. If there is a lot less mass then the impossible could be achieved even with less than ideal [for melt] conditions. Just sayin.
Rotten ice is becoming a bit of a meme round here.
I have looked at 'rotten ice' previously.
http://dosbat.blogspot.co.uk/2015/03/rotten-sea-ice-in-summer.htmlThe result, using compactness, is that the 'rotten ice' is most apparent in the summer in the Peripheral Seas (Beaufort round to Laptev).
By late summer, at the Autumn equinox, compactness has fallen from around 0.7 to around 0.5. This means the ratio of area to extent has fallen such that within a grid box where there is ice defined as extent (>0.15 or 15%) one might expect that in the 1980s one would have 3/10 open water. But by the post 2007 period one would expect to see 5/10 open water, or 1/2 open water.
Looking at compactness for the same region right now. It is 0.4992, or half open water, half ice. Sounds alarming? Portends disaster?
Well, no, actually it's in the normal range
for recent years.
When I say it is normal I stress that we should not lose track of how it was. Taking 18 July data, I've not got round to downloading more recent data, the 1979 to 1987 average compactness on 18 July was 0.71, or 3/10 open water, 7/10 ice. For the 2007 to 2015 period compactness on 18 July averaged 0.55, or 1/2 open water, 1/2 ice. That is a stunning change, similar to my findings in that blog post for September.
But what of the post 2007 period? Here is the data:
Comp Anomaly StdDevs
2007 0.4729 -0.0721 -1.47
2008 0.5903 0.0453 0.93
2009 0.5696 0.0246 0.50
2010 0.6171 0.0720 1.47
2011 0.5323 -0.0127 -0.26
2012 0.4997 -0.0453 -0.93
2013 0.5372 -0.0079 -0.16
2014 0.5870 0.0420 0.86
2015 0.4992 -0.0459 -0.94
Compactness is the actual compactness for 18 July in the stated years, anom is the difference from the average, and StdDevs is the number of standard deviations away from the average. Note that it is hard to tell the diference between compactness in mid July 2015 and other years, there is no trend to speak of, and at only -0.94 standard deviations this 18 July is low, but not exceptionally so. 2013 alone shows how compactness is not the whole story, in 2013 on 18 July compactness was as near as damn it 1/2, it did not result in a record low, rather the second highest minimum extent for the post 2007 period.
1) There is no indication in ice state, as meaured by compactness, of an iminent crash as the behaviour over the last few years does not show strong deviations from the range of post 2007 behaviour. (This applies equally to other indices)
2) If models were finding a problem with handling this ice (at least PIOMAS is not - it assimilates the gridded concentration from which Wipneus calculates area and extent), then it would apply to the full post 2007 period. We have had 7 summers since 2007, now we're well into the eighth, and if PIOMAS is wrong (overstating thickness) then it's hard to see how this has not yet manifested as a large drop in area or extent.
3) There is a lot of excitement about rotten ice round here, much of it is not founded - I don't want to make myself more unpopular round here, but this is simply the case! This 'rotten ice'
will get worse in the years to come, it
will play a pivotal role in the coming transition to a seasonally ice free state. But it is not behaving in such a manner as to indicate highly abnormal increase in rotten ice in the context of the post 2007 period portending a rapid crash. Instead the behaviour is pretty average for recent years.
4) However in a longer term context ice state in recent years underscores strongly the highly abnormal state of the pack post 2007, late summer in the peripheral seas has around 1/2 open water, in the first decade of the setallite decade it was only about 1/3 open water. 2015 will add another year to the
repertoire of behaviours post 2007. 2015 will add to the data that supports the researcher who coined the term 'The New Arctic', for that is what we are all following.
