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!
And just in time - I'd say - to have a look at how much divergence and drop in concentration was caused by the small cyclone that was discussed in this previous blog post. Commenter A-Team has already used the KlimaCampus/Wipneus images for an animation, and here's my own version showing the effect in that part of the ice pack below the cyclone, from May 26th to June 2nd:
There is clearly an effect, with open water between floes showing up all over the place, but still not as pronounced as the ACNFS model had it. In fact, none of that has showed up on the lower resolution SIC maps (CT and NSIDC, see ASIG), except for the Uni Bremen SIC map, which already has a decent 6.25 km grid. Of course, the gaps between ice floes can clearly be seen on the LANCE-MODIS satellite images now that the cloudy cyclone has finally moved away (click for a larger version):
Chris Reynolds has a good analysis of the difference between the ACNFS/ HYCOM forecast and observations, in his latest May 2013 Status blog post:
In my post on the Beaufort breakup of February 2013, link, I closed by observing that HYCOM showed a large opening of open water off Banks Island, which was not seen in reality (IR satellite images). I noted that this seemed to be because the modelled ice was stronger under tension than real sea ice. This is because the February breakup was driven by the ice being pulled clockwise by prevailing winds, so when the ice was put under tension along the Alaskan coast, this was relieved by a succession of parallel fissures opening. In the HYCOM model these fissures didn't open, so the net movement was revealed by a single area of open water (covered by thin new ice) rather than parallel fissures.
I think we have a similar situation in HYCOM during the May storm. This time the decline of concentration has been over a larger region than in HYCOM (as seen in Bremen). With HYCOM producing a centralised area of very low concentration due to the surrounding ice not forming the fragmentation seen in reality (MODIS/Bremen).
This also helps to cast light upon the driving factor behind the reduction of concentration and consequent thinning. The issue here is whether the reduction of concentration is due to movement of ice or melt where the ice is. Given the behaviour of HYCOM and the similarity of behaviour with the February breakup, it seems to me that it is net divergence of ice that is predominantly lowering concentration, not melt.
So it's safe to say that the ACNFS forecast didn't turn out to be real, but that doesn't mean that nothing happened. The ice pack under the cyclone received quite a thrashing, with ice floes getting broken up by wind and waves, with smaller floes perhaps getting washed over and turned around, and who knows, maybe even some warmer waters were brought up due to Ekman pumping. Like I wrote four days ago it was the combination of the ACNFS forecast with the weather forecast that made my eyebrow arch.
Let's see what ECMWF has in store for the coming 6 days:
While the cyclone has moved to the Canadian Archipelago doing some churning over there for a day or two, a high pressure area is bathing the Kara/Barentsz area in sunlight, as is the part of the ice pack that has been diverged in the past week. The cyclone then returns with some pretty low pressures (980 hPa), stays for a day or two and then fizzes out. More on this in the upcoming ASI update, this weekend.
Edit: Forgot to insert the latest DMI sea level pressure map that shows the cyclone near the CAA and the elongated high pressure area over the Siberian coast:
Just to be clear, if it weren't for the divergence, I wouldn't be reporting on this. Cyclones are normal at any time of the year, and I'd be wearing myself out very fast if I were to report on each and every one. But what makes this event noteworthy, is the fact that it is taking place while most of the ice pack is first-year ice because of last year's record smashing melting season. This makes the impact more noticeable. The other interesting thing is that the cyclone has been so stable for quite a stretch. Who knows, maybe we'll see more of those.
For now we simply note this event and await developments. After all, June has just started and we still have three months of melting ahead of us.
PS Back in March a paper was published that discusses some of these things: Cyclone impact on sea ice in the central Arctic Ocean: a statistical study, Kriegsmann and Brümmer, The Cryosphere Discussions (PDF).