Monday, 15 August 2016

Nevan's Arctic Sea Ice blog

For details of the Arctic sea ice melt

ASI 2016 update 5: big cyclone

ASI 2015 update 5

13 August, 2016

During the melting season I'm writing (bi-)weekly updates on the current situation with regards to Arctic sea ice (ASI). Because of issues with data based on the SSMIS sensor aboard DMSP satellites, I mainly focus on higher-resolution AMSR2 data from the Japan Aerospace Exploration Agency (JAXA), as reported on the Arctic Data archive System website. I also look at other things like regional sea ice area, compactness, temperature and weather forecasts, anything of particular interest.
The animation on the right consists of NSIDC
sea ice concentration maps, one for each 
ASI update.
Check out the Arctic Sea Ice Graphs website (ASIG)
for daily updated graphs, maps, live webcam images, and
Arctic Sea Ice Forum (ASIF) for detailed discussions.
August 13th 2016
In the previous update I wrote with regards to the 2016 trend line on the JAXAsea ice extent graph:
If it now somehow manages to end the month between 2011 and 2015, there's still room for August weather to keep the race exciting.
The 2016 trend line managed to end July right between 2011 and 2015, it is still in 3rd position as we speak, and now August weather is going to keep the race exciting. Another big cyclone is on its way and will hit the ice pack the day after tomorrow (no pun intended). This storm will not be as intense as theGreat Arctic Cyclone of 2012, but it will be almost as big, and linger for a few days. I think it's the second biggest storm I have seen since starting this blog, back in 2010.
It's difficult to tell whether this storm will have as much of an effect as GAC-2012 had. The ice pack was much weaker back then due to plenty of periods that were conducive to melting, in other words melting momentum. There hasn't been much melting momentum to speak of this year, as there has been little preconditioning of the ice pack during May and June, and cloudy conditions kept dominating the Arctic up till last week.
There has been a second kind of momentum, though, caused by the preceding mild winter and the spectacular retreat at the very start of the melting season. Snow cover melted out really fast and sea surface temperatures have been as high as they've ever been. A handful of cyclones so far have helped disperse the ice pack, with quite a large zone of ice, jutting out from the Central Arctic towards the East Siberian Sea, about to bear the brunt of the big storm (source:Uni Bremen):
UB SIC Siberian 20160807-12
When the Great Arctic Cyclone hit in 2012 all of the weak ice in this zone detached from the main pack and was annihilated. We'll have to wait and see if something similar can happen this time around.
Sea ice extent (SIE)
As said, the 2016 trend line on the JAXA SIE graph keeps moving downwards steadily:
With melt ponds starting to drain and freeze over, and lots of ice flashing back into the satellite's range of vision, CT sea ice area's behaviour has been more erratic. The 2016 trend line has been flat-lining somewhat the past couple of days, but a top 3 position is still in reach:CTSIA20160811Remember, CT hasn't updated their data since the SSMIS satellite sensor aboard the DSMP F17 satellite started relaying faulty measurements, but over on theForum Wipneus keeps calculating what the numbers would be, based on his reverse engineering of CT's method to calculate SIA.
With SIA staying relatively stable and SIE going down, compactness will inevitably go up again. A higher compactness percentage means that the ice pack is getting more compact. Melt ponds were counted for SIA, but now that they're draining/freezing over, SIA and SIE move closer together again.
Here's how things look on the CAMAS graph, where I use CT SIA numbers divided by MASIE extent numbers:CAMAS 20160811
For a more thorough explanation on compactness read the Melting momentum part 2 blog post.
Weather conditions
Here's the animation of Danish Meteorological Institute SLP images showing the distribution of atmospheric pressure during the past two weeks:
The animation shows that here has actually been a couple of days where high pressure took over the American side of the Arctic, forming something that could be called a Dipole, except that the low pressure still dominated much of the Arctic. This is probably the other reason the ice pack has become more compact and sea ice extent kept going down steadily, charging open water with some late sunshine on the Pacific side of the Arctic.
But now the forecast we're all waiting for. Let's see what the ECMWF weather forecast model has in store for the coming 6 days (click for a larger version, and go to the ASIG Forecasts page for daily forecasts): ECMWF2016-5
There it is, massive low pressure. This baby is going to go well below 980 hPa on Tuesday. The Tropical Tidbits website shows an ECMWF forecast map that has it go all the way down to 969 hPa:
Now, GAC-2012 bottomed out at 963 hPa and stayed around 970 hPa for a day or two, but this storm has got nothing to be ashamed of, with a couple of days of 980 hPa following the trough. There have been three other notable cyclones this year, with one bottoming out at 973 hPa on June 21st (fizzling out immediately after that), but this one takes the cake.
So, that means lots of winds, lots of waves, lots of mixing and churning. But cyclones also bring colder temperatures with them and it's already mid-August. Flash melting and a few days of possible increased SIE decrease may be offset by a freezing ice pack core where not much will be happening extent-wise until the minimum.
Here's the animation showing the GFS weather model temperature forecast maps for the coming week, as provided by  Climate Reanalyzer:
 CCI temp-5
Freezing air temperatures all over the Arctic. But of course, it's no longer air temperatures or solar radiation that are melting the ice. Now it's all up to bottom melting, and looking at current sea surface temperature anomalies, conditions are very similar to those of 2012. Close to the ice, that is. There is much more heat this year, both in the North Pacific and the North Atlantic:
DMI SSTA August 11 2012 vs 2016
It's very simple. This melting season would've broken the 2012 record, if the Arctic hadn't been dominated by cloudy weather almost all of June, July and August. The fact that this year is still a contender for a top 3 position, speaks volumes. But will it make it into the top 3, a question I've been asking since ASI update 3?
This very large cyclone, possibly the strongest summer cyclone on record after 2012, may give us an answer to that question. There's still a month to go before the melting season ends, but in the next few days all eyes will be on this monster storm.
Oh, and by the way, it looks as if both the Northern Sea Route and Northwest Passage will be open again.

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