If you want to know where you're going, it helps to know where you're coming from. This also goes for Arctic sea ice. Even though the long-term trend is down, it's difficult to tell what will happen in any given melting season. Two things can help us get an idea: initial sea ice state and subsequent weather conditions. This post is about how the sea ice has fared throughout the freezing season and what shape it was in last month when sea ice growth slowly came to a grinding halt and winter started to make way for spring.
For that I'm going to compare the 2014/2015 freezing season with those of the preceding three winters, just like I did last year. That way we can see how the past winter compares to the winters preceding the 2012 record smashing melt and the two rebound years following it. If you want to compare some of the images below with other freezing seasons, you can dig through the 2011/2012 and 2012/2013 winter analyses. And click on the images if you want to have a closer look.
We kick off with the AARI ice age maps for the end of April that show the amount of multi-year ice (MYI) in the Arctic (brown colour):
Last year's genetically modified rat has been replaced by a woolly mammoth (I'm sorry, I can't help but seeing animals in these maps), but the amount looks about the same. What is interesting this year is that the MYI looks a lot more fragmented on the Pacific side of the Arctic, with some young ice (pink) and even open water in the Chukchi Sea.
This has everything to do with a cracking event that took place a couple of weeks ago. It wasn't as spectacular as the cracking event of February/March 2013, but it was still quite big, and more interestingly, it took place at the very end of the freezing season. We have to wait and see if there's any consequence for the melting in this region. On the one hand there's a lot of first-year ice (FYI) between the MYI floes which could melt out early. On the other hand heat might be released to the atmosphere, cooling the water below the ice, making it more resistant to melting.
Either way, it's visible on different maps, such as the ASCAT radar images. Here's a comparison for day 109 (April 19th):
You could roughly say that the whiter ice is the multi-year ice, and the darker ice is first-year ice. There are two interesting things that can be seen here (in the white circles). First of all that great (though cracked) barrier on the Pacific side of the Arctic that could become a determining factor towards the end of the melting season. If the ice there manages to survive, like in 2010 for instance, there will be no record. If it does melt out, like in 2012, it's adios, amigos.
The second feature is the fact that the zone around the North Pole (the black dot in the smaller white circle) is dark, with no white anywhere nearby. I think it's fair to say that this is unprecedented, and it means that the North Pole is most probably covered with first-year ice. This doesn't mean anything in itself, as it will take some exceptional weather to start attacking that part of the ice pack, something we haven't really seen in other years when the edge between MYI and FYI wasn't that far from the North Pole either.
On the other hand, there was open water all the way to 86 degrees North last September, and we have seen open water in the Laptev Sea extend further and further northwards in recent years. So this is definitely something with spectacle potential, but again, it will need some of that Arctic voodoo.
There's one more ice age comparison left, that basically shows the same. These ice age maps made by Tschudi, Maslanik and Fowler (source) form the basis for the Arctic sea ice age maps that are featured in the NSIDC monthly analyses at the end of the melting and freezing seasons:
A lot more multi-year ice than in 2012 and 2013, and a lot of blue between the red in the Beaufort and Chukchi Seas.
Edit May 11th:
I forgot to make mention of these two videos Jim Hunt from The Great White Con put up a few weeks back, showing the movement of the ice during winter.
ASCAT radar images:
And JAXA AMSR-2 RGB:
Sea level pressure and ice drift
The only possible reason for the North Pole to be covered with first-year ice, is the Transpolar Drift Stream pushing the ice away from Siberia towards the North of Greenland and the Canadian Arctic Archipelago, the Arctic's Fort Knox where the last remaining thick ice is located. But the TDS is pushed by winds, and winds are pushed by differences in sea level pressure (SLP).
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.
The yellow, orange and red represent high pressure, the purple and blue represent low pressure, and it's between these two sets of colours where all the wind action takes place. The past winter looks quite similar to that of 2013/2014, except that the low pressure seems to reach further towards Eastern Siberia, which is no wonder given a long series of cyclones blowing in from the North Atlantic during the second half of winter.
It's also clear that from December onwards the winds on average blew straight to the Canadian Arctic Archipelago, especially the last two months of the freezing season:
Unfortunately many of the IFREMER/CERSAT sea ice drift maps I like to use to show wind patterns and thus sea ice drift in more detail, are missing this year, except for this one, which shows there was quite a bit of transport through Fram Strait as well during March:
Air and sea surface temperatures
For temperatures we turn again to NOAA's Earth Science Research Laboratory daily mean composites page. The comparison below shows temperature anomalies (-5 to +5 °C) for two halves of winter:
Two things stand out in the second half of the freezing season: the bitter cold that hit the Northeastern US also covering Hudson and Baffin Bay, compensated by less cold temps over Siberia, probably caused by the Atlantic Cyclone Express I mentioned previously. Unlike last year, there is hardly any orange and red to be seen from January to March.
Last year the 2013 volume rebound had almost completely disappeared at the start of the 2014 melting season, and those high temperature anomalies probably had something to do with that. This year some of the volume rebound has lingered (see last PIOMAS update) and that's probably because the anomaly is smaller.
As for sea surface temperatures (caveat: I don't know how trustworthy SST maps from the daily mean composites page are):
The most noteworthy aspect is the warm water to the south of Alaska, which has to do with the PDO currently being positive.
The Naval Research Laboratory has been sharing different 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:
This seems to confirm what is visible on the ice age maps: the thick ice has been pressed against Greenland and the Canadian Arctic Archipelago. In fact, as Chris Reynolds pointed out in a recent blog post using PIOMAS data, it seems that this is where most of the volume rebound is situated. Here's a bar graph he produced to show the differences in volume with April 2013 (following the record breaking 2012 melting season):
A couple of weeks ago CryoSat-2 sea ice thickness maps were released by the Centre for Polar Observation and Modelling (University College of London),but unfortunately there's no archive (yet), so I can't compare to other years. Here's the current situation according to CryoSat-2:
We can see some of that thicker ice transported all the way to the East Siberian Sea.
Except for the Central Arctic the ice pack is more or less in the same initial condition as previous years. This essentially means that anything is possible, except for an ice-free Arctic (sea ice area/extent below 1 million m2) come September. And you can quote me on that. ;-)
If weather conditions are similar to 2012 this melting season will end up very low, possibly record low. If it's cold and cloudy like in 2013, or things don't move at all like in 2014, the melting season will end up relatively high. With relatively I mean relative to the post-2007 era, as it will definitely be very low compared to the long-term trend.
Things to watch out for:
- Will the Northwest Passage (central route) remain closed for a third year in a row? The Northern Sea Route is bound to be open again.
- Will the multi-year ice that has been transported from the Central Arctic into the Beaufort and Chukchi Sea form a barrier that can withstand whatever the melting season throws at it? Or will it melt, with consequent volume losses?
- Will the Laptev Bite appear yet again, and if so, how far north can it reach? Will the North Pole, currently covered with first-year ice, stay covered for the entire melting season?
So, that's it for phase one: initial sea ice conditions. We now turn towards the second phase that for a large part determines melting momentum through melt ponds. This will be the central theme of the first few ASI updates, starting next week. If you can't wait and want to know more details, check out the various threads on the Arctic Sea Ice Forum.