With another interesting freezing season behind us, it's time to compare to previous winters and get an idea of this melting season's foundation. As we have seen in the last two years, the start of the melting season plays an important role, and so it might very well be that the end of the freezing season plays a role as well (what holds for the Arctic summer often is the opposite during winter). If only for the fact that the end of the freezing season is immediately followed by the start of the melting season. Sorry for being so simplistic.
OK, we'll repeat the format from last year and compare the 2013/2014 freezing season with three other freezing seasons. In this case, I have chosen the last three winters (ie preceding the 2011, 2012 and 2013 melting seasons). No 2007? No 2007. I know it's blasphemy, but we have to move on. Click on the images if you want to see a larger version.
It's clear that after last year's 'rebound' the Arctic now contains a lot more multi-year ice than in the last 3 years, as can be clearly seen on these AARI ice age maps for the end of April:
2011's vomiting cow doesn't look all that smaller (the brown colour represents the multi-year ice), but this year's genetically modified mouse is still a tad bigger, with a large bulk of multi-year ice taking up position in the Beaufort and even some of the Chukchi Sea. Whether this will prove to be a protective barrier, as witnessed in 2010 and 2011, remains to be seen.
These ASCAT radar images also show that this year the ice pack contains a lot more whiter ice. Here's a comparison for day 109 (April 19th):
Ice age doesn't necessarily tell us anything about ice thickness, and the white colour doesn't either. As the NSIDC explains in their latest April summary:
The ASCAT sensor measures the radar–frequency reflection brightness of the sea ice at a few kilometers resolution. Sea ice radar reflectivity is sensitive to the roughness of the ice and the presence of saltwater droplets within newer ice (and, later in the season, the presence of surface melt). Thus older and more deformed multiyear ice appears white or light grey (more reflection), whereas younger, first-year ice looks dark grey and/or black.
Of course, it doesn't mean the ice isn't thicker either.
The NSIDC summary is also accompanied by the yearly ice age distribution map, now provided by Dr. Tschudi from the University of Colorado. I've combined it with the maps from 2012 and 2013 on the right.
Other than a lot of second-year ice (blue) last year, there's also a lot more white (4+ years old) than we've become accustomed to, but a large part of it is now sitting in the Beaufort. If it doesn't prove to be a barrier, it could get lost again. Another reason for this increase in multi-year ice (besides last year's 'rebound'), according to the NSIDC, is "the predominant recirculation of the multiyear ice pack within the Beaufort Gyre this winter and a reduced transport of multiyear ice through Fram Strait maintained the multiyear ice extent throughout the winter".
As we'll see below.
Sea level pressure and ice drift
The movement of ice floes is largely determined by wind, and wind is largely determined by sea level pressure gradients. So let's first have a look at SLP maps from NOAA's Earth Science Research Laboratory (daily mean composites page). I have divided the freezing season up into 3 parts with a duration of two months each:
It seems 2013 was the odd man out, because 2011, 2012 and 2014 look remarkably similar. This, of course, doesn't mean that this melting season will follow those of 2011 (record tie) and 2012 (record smash), but it's noteworthy nonetheless. As it was last year.
I have combined these IFREMER/CERSAT sea ice drift maps to show how the ice moved in the recent October-March period:
It indeed seems there hasn't been much transport through Fram Strait, and much of the ice has recirculated, which should improve overall ice quality.
Air and sea surface temperatures
Now to have a look at temperatures. For that we turn again to NOAA's Earth Science Research Laboratory daily mean composites page.
The first half of the 2013/2014 freezing season wasn't really irregular. Of course, it was very warm in a large part of Siberia, but it's after New Year's Eve that things get really interesting temperature-wise, with record temperatures being recorded in places like Svalbard and Alaska.
This NCEP air temperature map including April shows how temps have been the highest on record in the 70 to 90N area of the globe (from this blog post by Diablobanquisa):
I've made separate temperature anomaly maps for the first three months of the year, and things really look hot (compare for instance to last year):
Of course, this doesn't mean that temperatures were high during January, February and March, it was plenty cold in the Arctic. But the anomalies are very high, and every degree less cold means the ice thickens less. How much less, we don't know, but according to PIOMAS the volume rebound from the 2013 melting season has been all but negated. And the relatively mild temperatures probably have played a big role in this.
It probaby also played a role in the amount of snow cover on the Northern Hemisphere (see for instance March), but we have to wait and see how that plays out.
I don't know how trustworthy SST maps from the daily mean composites page are, but here too the 2013/2014 freezing season really stands out during the second half:
The Naval Research Laboratory has been sharing several sea ice maps for a couple of years now from their ACNFS model. Although I don't know how reliable their thickness maps are, it's still useful to compare this year's map to those of previous years:
A lot of dark red pressed against Greenland and the Canadian Arctic Archipelago, but a lot of blue as well, and again we see all that yellow towards the Alaskan coast.
Another source of information comes from the SMOS satellite (see this blog post from 2012) that has been validated extensively the last couple of weeks during various missions in the Arctic. The data has been converted by commenter Wipneus - who regularly posts SMOS updates on the Arctic Sea Ice Forum - and compared to the previous three years:
Keep in mind that SMOS can only measure ice up to 0.5 metres, and the differences with previous years are minute, but it's a comparison and that's what this blog post is all about.
I'll finish with another graphic produced by Wipneus and posted on the ASIF, this time depicting the change in thickness compared to 2013, as produced by the PIOMAS model:
This clearly reflects the ice drift maps from above, with ice being pushed from Siberia to Greenland and the CAA, leaving thinner ice in its wake. It suggests to me that the Northern Sea Route could be opening up again, but perhaps the Northwest Passage remaining closed for a second year in a row.
Personally, I don't think the 2012 extent/area record will be broken this year, just like 2007 was followed by a couple of 'rebound' years. The bastion of older ice has been re-inforced, although part of it has moved out into a zone where it could be either vulnerable or hang on long enough to prevent any records.
Still, given the PIOMAS volume wipe-out and the high temps during the latter half of the freezing season, I do see how this year's minimum could come close to or even surpass that of 2012. Of course, it all depends on what the weather does. And the start of the melting season is very important as well.
I hope you enjoyed this quick overview. I will soon start posting regular Arctic Sea Ice updates, because there are already lots of interesting things going on. Check the Arctic Sea Ice Forum if you can't wait for the updates (ignore the safety warning).