Arctic Sea Ice

As we approach the final stretch...

For years we've talked about one of the most fascinating phenomena of Arctic sea ice loss as it progresses from year to year: The moment when the ice disappears regardless of the weather. We've seen some of that, back in July 2012, when extent and area numbers kept going down steadily, even though weather conditions weren't conducive to melt and should have caused a marked slowdown on the graphs (like they did in the preceding years). Some time later I concluded that this had to do with what I now call melting momentum.

The idea is that if during May and July the ice gets hit by lot of sunshine, lots of melt ponds form and they soak up a lot of heat. This doesn't immediately cause the ice to melt, but starts to make itself felt towards the later stage of the melting season. The built-up momentum keeps the melting going. For this reason I've been focusing on things like compactness, that tells us something about the amount of water within the ice pack, whether open water or melt ponds (satellite sensors can't see the difference).

But does this still hold true? Will there be a moment when the ice disappears regardless of melting momentum as well? We saw in 2016 that there wasn't much melting momentum built up during May and June, but despite the cloudiness, a record warm winter and persistent high air temperatures were enough to make the ice vulnerable enough for a big cyclone and massive dipole to have 2016 come in second on almost all graphs (see this overview). Yes, melting momentum is important, but there are other things at play as well, of course.

NSIDC Compactness (are divided by extent) as of July 29th

Now, this year has been extremely interesting so far. For the third time in a row, the winter preceding the melting season was relatively mild, the maximum was low (second lowest on record), and the trend line on many a graph went low from the get-go. Not as low as 2016, but low. However, as in previous years, clouds moved in and things slowed down to a crawl, taking the trend line as high up as 11th lowest on record on the JAXA sea ice extent chart last week. But then this happened in the last couple of days, suggesting spectacular melting on the Pacific side of the Arctic:

So, what's going on?

2016 Mega-Dipole

As reported in the last ASI update, the forecast Dipole has now set up. Yesterday's last analysis chart provided by Environment Canada, at 18Z, showed the high pressure moving in via the Bering Strait at 1037 hPa, while a rapidly weakening storm that had moved in from Siberia (lowest central pressure was 967 hPa, two days ago) was still at 974 hPa on the other side of the Arctic. This then evolved to a massive 1041 hPa on one side of the Dipole, and 977 hPa on the other:

That's a humongous pressure gradient of 63-64 hPa! You don't see that often around this time in the Arctic, a not so nice story for the grandkids. Right now, the high is still at 1041 hPa, but the low has weakened further to 980 hPa. That's still a pressure gradient of 61 hPa.

It means very strong winds are blowing over the ice pack, from Siberia to Canada, compacting the ice pack and further pushing open water towards the pole, as can be seen on this animation of Uni Bremen sea ice concentration maps:

If one looks carefully at the ice in the so-called Wrangel Arm, you can clearly see the ice flash in and out of existence. There comes a point where the ice no longer flashes back, but in the meantime it makes for wild swings on the CT sea ice area graph, as calculated by Wipneus:

2016 Arctic cyclone, update 3

Two days have passed since the previous update, and in those two days the storm re-intensified, bottomed out at 971 hPa (slightly higher than the first lowest central pressure of 968 hPa), as can be seen on the image on the left, provided by Environment Canada. It quickly weakened after that, but lo and behold, the image on the right shows it has re-intensified again and is currently at 971 hPa as well!

Just like that, as if it's nothing. Which brings us to the first of three questions (there were two in the previous updates, but now there's a third one at the end of this blog post):

1. Is this a Great Arctic Cyclone?

I'm still not entirely sure how this storm will rank, compared to previous storms. Remember the quote from Simmonds and Rudeva paper I mentioned in update 1:

The plot shows that AS12 was at the tail of the distribution and, at 966.38 hPa, was the lowest in our record, beating the previous deepest (966.94 hPa) (for a storm at 06UTC 7 August 1995) by 0.56 hPa. The next lowest central pressure, 969.23 hPa, was associated with a cyclone at 06UTC 22 August 1991, followed by the fourth lowest storm central pressure in the earlier part of that month 00UTC 7 August 1991 (970.47 hPa).

But it's definitely a very powerful storm, and even if it doesn't boast the lowest central pressure, all these re-intensifications will probably have it score high in other requirements for GAC nomenclature. And that reminds me of something I wrote back in 2012, following a quote that is highly relevant today:

“This past week’s storm was exceptional, and the occurrence of Arctic storms of extreme intensity is a topic deserving closer investigation,” noted Walsh. “With reduced ice cover and warmer sea surfaces, the occurrence of more intense storms is certainly a plausible scenario. The limitation at present is the small sample size of exceptional events, but that may change in the future.”

That last bit is the reason I'm hesitant calling this the Great Arctic Cyclone of 2012, or Arcticane, or some such. What if we see a similar cyclone in 2013 or 2014? We'll run out of names.

Mind you, I don't want to downplay the importance and magnitude of this storm, it's by far the biggest thing I have seen in the Arctic since I started the blog, but to me this whole event isn't about the storm itself, but about a possible new regime - a new aspect of the new abnormal - with big summer storms in the middle of the Arctic.

I called it the new abnormal at the time, but if this becomes 'normal' (compare coverage of this storm to 2012, for instance), then what cachet does the name 'Great Arctic Cyclone' still have?

Arm's race (and a storm)

As I write this, a storm is battering the ice pack on the Pacific side of the Arctic. It's not as huge as the Great Arctic Cyclone of 2012, but it's pretty decent as far as cyclones go, and it's doing its thing in that part of the Arctic where the ice pack looks weakest, but was strongest at the start of the melting season.The timing of this event is perfect for discussing one of the most important aspects of this melting season.

The image on the top right shows the ice age distribution at the start of the melting season, red being the oldest multi-year ice at that time. Due to a very intense high pressure area over the Beaufort Sea at the end of the freezing season, heavy winds drove the ice pack apart there (a so-called cracking event), causing this multi-year ice to become interspersed with very thin ice. That's the dark blue spots between all the red.

During the very first phase of the melting season the Beaufort Sea region witnessed a heat wave causing a lot of this thin ice to melt out. Because the ice pack wasn't pushed back together again, many of the multi-year ice floes were surrounded by warming waters, and ever larger holes within the ice pack on the Pacific side of the Arctic started to form. The animation below shows what happened between week 27 and week 32, or June 29th to August 9th:

Just towards the end of the animation the holes are showing up. Unfortunately these maps aren't updated until the minimum has hit, but we can still get an idea of what happened after August 9th by checking out the sea ice concentration maps provided by the University of Bremen. The following animation shows how the holes separate a so-called 'arm' of multi-year ice from the rest of the ice pack:

Poof, it's gone

One of the reasons for setting up the Arctic Sea Ice Forum, was to increase interaction and make more space for visual gems that do not fit the narrow comment section of this blog (check out for instance the Jakobshavn glacier thread).

One of those gems was posted yesterday by commenter epiphyte, who for the past month tracked one single ice floe in the Laptev Sea. What I like about this, beside the visual appeal of the images of course, is that it shows that ice doesn't disappear gradually, but suddenly. That's to say, for those who are watching from above.

Here's epiphyte's explanation of what he did:

It troubles me that so much weight is given to the rate of decline in area+extent as an indicator of the progress of the melt season. I think that this is becoming less and less relevant as the volume distribution becomes more even every year - I.e. you would expect that the year there is an ice-free September, there might still be a very high percentage of the April area/extent in early August.

Here today, gone tomorrow. I'm not saying it's this year - but on the year it happens, it will happen fast - and IMO anyone tracking progress by comparison with past years CT area decline will be very surprised to see it go.

To illustrate what I'm reaching for at I followed the melt progression of a large, high-albedo ice floe under favorable conditions. The image below is a series of snapshots of a ~300km^2 ice floe on the Laptev/CAB boundary  (~79N , 110E) taken from worldview between 01-jul and 01-aug. (see images below). For each image, I counted the number of pixels with > 50% luminosity on a 140x140 pixel array centered on the floe, cut from that day's 7-2-1 Terra/MODIS image.

As Peter Ellis pointed out earlier on the thread - anything you can see on EOSDIS is not slush. The floe we are looking at here is a contiguous, high-albedo (snow-covered?) ~300km^2 chunk of ice at the edge of the pack. It remains so from 01-26 jul. On Jul 27, it becomes a little less bright and loses 10% of its area. Three days later - poof. It's gone.

Click the image for a larger version.

In the meantime, the Arctic seems to be on for some of the most powerful melting weather we have seen this melting season. A prelude of it has already led to most of the Northern Sea Route opening up (just some last ice blocking Vilkitskiy Strait).

How things play out exactly, and what happens after that, will be discussed in the next ASI update.

New map on the block

Further down is a short update on the effects the SAC-2013 (Small Arctic Cyclone of 2013) has had so far, but first I want to draw some attention to a great new product that has recently come online, a sea ice concentration map with the highest resolution so far. When I started this blog the NSIDC used a 25 km grid, meaning that every pixel on their SIC map represented an area of 25 x 25 km, or 625 square kilometres, on the ground. IJIS had a 12.5 km grid and the University of Bremen even had and still has a 6.25 km grid.

Last year the GCOM-W1 (Shizuku) satellite was launched, with the AMSR2 microwave sensor aboard, and soon after that the Japanese space agency JAXA started to put out data. Alexander Beitsch from the University of Hamburg's KlimaCampus optimized the processing of this data, improving grid resolution to a stunning 3.125 km. This was part of his PhD in the framework of the IRO2 project that is being funded through the German Federal Ministry of Economics and Technology (BMWi). Sehr gut und danke schön!

There was just one problem with the sea ice concentration map that was produced, and that was that it was huge. 17 MB for just one image makes it difficult for us amateurs to play around with it. Luckily, the Arctic Sea Ice blog has some very smart bunnies on its member list, and it was Wipneus (well-known for his work on PIOMAS data) who managed to reduce the file size by ten times. For the time being he is putting those images on a separate Google Site. Thank you, Wipneus!

If this is real...

As usual, it's all about the if. Allow me to explain what this is about:

In the first Arctic Sea Ice update of the 2013 melting season that was posted a couple of days ago, I announced that a cyclone was forecasted to move over the Arctic Basin and stay there for a while. It's been there for a couple of days now as can be seen on this animation of Danish Meteorological Institute SLP images:

It's not particularly strong (especially not compared to GAC-2012), but it stays in the same spot for quite a while and so is bound to have some effect on the ice below. Now, according to the Naval Research Laboratory's ACNFS forecast model, this effect is quite pronounced. And to show you just how pronounced, here's their sea ice concentration animation from May 22nd, with a forecast up to June 6th:

Arctic summer storm open thread 1

As the storm is still there, big, but no longer strong, and comment threads fill up quickly, I figured it's time for an open thread. And yes, it's a bit of an update as well, with interesting comments and graphs.

But first the updated animation. Now that the swathe of ice floes in the East Siberian Sea has detached itself, it's time to slowly say bye-bye to the ice atoll in the upper left corner:

sea ice concentration maps courtesy of the University of Bremen

Here's a comment by Rob Dekker that I want to put the spotlight on, because it's very interesting and gets to the core of the consequences of this storm:

Further detachment

This isn't an official Arctic summer storm (ASS) update, but it comes damn close to one. The thing is that the last domino hasn't fallen yet, as the storm is still there, though less powerful.

In yesterday's Arctic storm update I mentioned how a large swathe of ice floes had almost detached itself from the main pack. Well, I think it's as good as completely detached now:

We already speculated about such an event back in 2010, the first melting seasson that was covered on the ASI blog, in a blog post called Breaking away from the pack:

Not so long ago, in one of the comment sections, we discussed whether it would be possible for a large piece of the ice pack to separate itself from the main body of ice in the Arctic Basin.

(...)

I'm not sure, but I think the ice pack falling apart with patches of highly concentrated ice breaking away from the pack could be a precedent in the satellite era.

(...)

What if that forecasted high-pressure system over the Beaufort Sea starts to develop for real next week and the Beaufort Gyre kicks into gear again, spurred by westerly winds? One would think the small patch(es) in the Beaufort Sea would get pressed into the central pack again, but perhaps the bigger patch in the East Siberian Sea would get swirled loose by the winds blowing westwards.

Okay, it took eastward blowing winds. Close enough. ;-)

I zoomed in a bit and made an animation of the recent changes on the Uni Bremen sea ice concentration maps:

Arctic storm part 3: detachment

Yes, ladies and gentlemen, the Arctic summer storm is still there. After approximately 48 hours (which is long for an Arctic summer storm) it has weakened some compared to yesterday or the day before, but as far as I can see sea level pressure in the centre of the storm is still around 970 mb, which is low.

And so we're still seeing significant changes on the Uni Bremen sea ice concentration maps. Here's the animation from August 3rd to 7th:

That large patch of sea ice in the East Siberian Sea is almost entirely detached from the main ice pack. This is something I for one have never seen before, and I wouldn't be surprised if it's unprecedented in the satellite era. We have speculated a lot about this in previous melting seasons, but now the moment seems to have finally arrived. The fact that the ice pack can get divided like this, is yet another sign that the ice is exceptionally thin, as thin ice gets pushed around more easily and melts quicker, leaving open space between thicker, slower moving ice floes.

I've also updated the animation of DMI sea level pressure maps that shows the development and position of the storm: