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Sunday, April 3, 2016

Neven Acropolis: Addendum to 2015/2016 Arctic sea ice winter analysis

by Neven Acropolis, Arctic Sea Ice Blog, April 2, 2016

A couple of things were missing from the 2015/2016 winter analysis posted a few days ago, and so I've decided to present them in this separate blog post. Most of these images come from the website of NSIDC research scientist Andrew Slater.
Another way to express how warm or not-cold the Arctic has been this winter, is through so-called freezing degree days. The NSIDC explains it as follows in the All About Sea Ice segment of their website:
The relationship between thermodynamics and sea ice thickness can be thought of most simply in terms of freezing degree days (FDD), which is essentially a measure of how cold it has been for how long. The cumulative FDD is simply daily degrees below freezing summed over the total number of days the temperature was below freezing.
In other words, the sum of the number of days below 0 °C multiplied by the temperature for each day. Here's a graph from the +80° N 2m Tair page on Dr. Slater's website that shows this year's FDD compared to those of other years:
FDD comparison
What can I say? This year's trend line is not only way outside of the percentile zones, it's falling off the chart. This comparison obviously corresponds well with the temperature charts and anomaly distribution maps I used in the 2015/2016 Winter analysis. But let me repeat that this isn't necessarily telling us anything about the coming melting season. As you can see, the blue line representing FDD preceding the 2011 melting season is rather high, but that melting season still managed to equal 2007, record holder at the time. Conversely, the yellow line is low, but the 2014 melting season turned out to be a second rebound year after the 2012 record breaking melting season.
Even though we don't know what will happen this coming melting season, we do know that those anomalously warm/non-cold temperatures have had a marked effect on the ice pack. As mentioned in the 2015/2016 Winter analysis the increase in sea ice volume so far this year is the lowest on record (PIOMAS will probably be updated in the coming week and I'm expecting March increase to be lower than the average of the past decade).
When it comes to sea ice extent and area, Cryosphere Today reported the lowest Arctic sea ice area maximum on record, as did the NSIDC for their Sea Ice Index (extent), and JAXA sea ice extent had the second lowest maximum on record (just 16K more than last year's record). As we can see on the JAXA SIE and CT SIA graphs this year's trend line is still the lowest of all in the 2007-2016 period:

That means that this year has a bit of a head start, and these maps provided by Dr. Andrew Slater display the differences in concentration between this year and the four years with the lowest minimums on record (2007, 2011, 2012 and 2015). Red means there's less ice now, blue means more:
Ice concentration comparison March 31Remember, you can also check the differences in sea ice concentration yourself by going to the Concentration maps page on the Arctic Sea Ice Graphs website by having a look at the University of Bremen's sea ice concentration maps from 2005 to now.
2015 also had a bit of a head start (1 million km2 less sea ice than 2012, for instance) and I warned people that this difference would disappear as soon as the easy ice on the fringes of the pack would have melted out, because the PIOMAS volume maximum was higher than any other year from the post-2010 area, meaning thicker ice further into the pack that reduces the melting rate. We haven't reached the volume maximum yet, as the ice pack thickens some more in the interior zones, but right now only 2011 had lower total volume than this year.
So, no similar warning this year. An average melting season will mean a top 3 lowest minimum, possibly a new record lowest minimum. Anything that resembles 2007 or 2012, and there will definitely be a new record. A lot of it will depend on the build-up of melting momentum during May and June. [Readers may note that the upcoming rate of melt in May and June will be dependent on the Arctic Oscillation Index during that period.  A positive index means warmth will be carried into the Arctic over the North Atlantic to the east of Greenland, while a negative index largely means this source of warmth will be suppressed. Watch here:  This effect is less significant as we go deeper into the summer months.] One more month to go.

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