Whoever said watching the Arctic during the melting season is boring, needs to put his glasses on. After a record low reflectivity of the Greenland ice sheet (with accompanying floodings on the west coast of Greenland), the calving of another enormous iceberg from Petermann Glacier, and the general rapid decline of Arctic sea ice despite adverse weather patterns, we can now add to the 2012 melting season bonanza the appearance of a cyclone the likes of which are rarely seen in winter, let alone in summer.
The storm came in from Siberia, intensified and then positioned itself over the central Arctic, reaching sea level pressures of below 965 mb in the storm's centre, engendering 20 knot winds and 50 mph wind gusts:
data source: Danish Meteorological Institute
The storm is now losing its strength and dissipating, but its effect on the sea ice has been enormous so far. In this phase of the melting season when decline starts to slow down, large swathes of sea ice just disappear from one day the next, and the next, and the next (which is why I refer to it as flash melting). It can clearly be seen on this animation of sea ice concentration maps that are updated daily on the Cryosphere Today website, showing the sea ice decline of the past couple of days:
Although technically not all of the ice that disappears on these maps is completely melted (some of it doesn't get picked up by satellite sensors due to clouds and waves submerging ice floes), the gale-force winds displace and break up ice floes, and churn the waters below causing warmer, saltier layers under the thin film of fresh water to mix upwards and melt the ice some more from the bottom. This storm is the worst thing that could have happened to an already weakened and dispersed ice pack.
One development on these sea ice concentration maps that stand out particularly, is the detachment of a large swathe of ice floes from the main ice pack. I've never seen such a thing before, and I wouldn't be surprised if it is unprecedented in the satellite era. But I guess that is what highly unusual Arctic summer storms can lead to.
The effects on the ice pack are also staring to get picked up on sea ice area and extent graphs. The most remarkable decline can be seen on this sea ice extent graph from the Danish Meteorological Institute:
That massive decline will probably get revised upwards in days to come (DMI has said it will be revised), but it is visible on other graphs as well, such as the IJIS sea ice extent graph:
And on the Cryosphere Today sea ice area graph the 2012 trend line has been in first place for the past 38 consecutive days, and 54 of the last 59:
It's an amazing sight to see this year's trend line so much ahead of record years 2007 and 2011, at this stage of the melting season. Suffice to say that this year's melting season is well on its way to breaking all records on all graphs out there. It's not a done deal yet, it never is in the Arctic, but chances are greater than ever.
So back to the storm. How unusual is it? Very unusual. The strength, the size, the location, the duration, all of it is highly anomalous. Someone on the Arctic Sea Ice blog proposed to call it the 'Great Arctic Cyclone of 2012', but this can probably only be done in retrospect. For who's to say that we won't be seeing more of these Arctic summer superstorms in the near future? Although scientific research on (mostly winter) cyclones dates back many decades, there are a lot of unknowns when it comes to phenomena such as these, if only because things are changing so rapidly in the Arctic.
This storm saw its genesis in northeastern Eurasia, and that has to do land with snow cover, as explained by this 2006 research paper by NSIDC director Mark Serreze (of Arctic Death Spiral fame):
While there have been no trends in the strength or persistence of the summer cyclone pattern over the period of 1958–2005, it is natural to speculate on its future behavior. Climate models are in near-universal agreement that Arctic warming in response to greenhouse gas loading will be especially strong. Results from the present study suggest that, at least in part, the summer cyclone pattern owes its existence to differential atmospheric heating between the Arctic Ocean and snowfree land. If patterns of differential heating change substantially, such as through earlier springtime loss of snow cover over land, or through changes in the presently strong summer net surface heat flux over the Arctic Ocean as the sea ice cover disappears, this may invoke changes in the summer circulation.
Earlier springtime loss of snow cover on land? It certainly looks like it in recent years:
data source: Rutgers University Global Snow Lab
Another factor is the sea surface temperatures of Arctic waters surrounding the cold ice pack. These have been extremely anomalously warm everywhere except in the Bering Strait and Chukchi Sea this year, and this probably helped the storm feed and sustain itself:
I'm not so sure that we're going to see smaller snow cover and sea surface temperature anomalies in coming years, and so I'm not sure either that we won't be seeing more cyclones of this magnitude. Hopefully not, as it would be the death blow for the ever more fragile ice pack. If the Arctic keeps coming up with unpleasant surprises such as these, an ice-free Arctic in September is a definite possibility before the decade is out. And no one wants to think about all the potential consequences this entails. But we must...
Posted by Neven on Friday, 10 August, 2012
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