(Image Source: DMI)
An Arctic cyclone that has persisted for nearly two weeks has now shifted to a region just north of the Canadian Arctic Archipelago, strengthening to a 980 mb low.
The low originated in the Beaufort Sea about two weeks ago. It transitioned to the central Arctic, remaining there for about a week, before finally moving to its current position over the Arctic’s thick ice.
Observations via Lance Modis satellite shots, CICE, JAXA, and Uni-Bremen, have shown a moderate but ongoing thinning of the ice pack beneath this persistent cyclone. Ice thinning appears to be driven by a combination of divergence, surface mixing in areas near the ice cracks, and by cyclonic forces that encourage upwelling of warmer waters beneath the ice.
As the cyclone is currently predicted to persist and strengthen, impacts are likely to continue and could potentially worsen over the coming days. These include:
- Diverging sea ice.
- Thinning sea ice via ocean surface churning and upwelling of deeper waters beneath.
- Influxes of warmer air behind the storm.
Since the storm is projected to intensify and to last for such a long time, we’ll be taking a more in-depth look at the above melt processes, how they may unfold, and why this particular storm may continue to cause trouble.
How Ekman Transport and Mixing Can Erode Sea Ice
Sea ice traps a layer of cold water near the ice. This layer is usually colder than areas of water as close as 20 meters below by about one or two degrees C. So even in winter, contact with deeper water can enhance bottom melt on the ice. As seasons change to spring and summer, a persistent sun plunges through the ice, further heating this layer just below the cold surface. This, 3-5 degree C warmer, water packs a bit more punch to heat and melt the surface ice. Usually, this layer doesn’t come into contact with the ice. But winds, tides and ocean currents can all stir up these deeper, warmer, layers enhancing ice melt.
In particular, cyclonic action generates upwelling through a process called Ekman Transport that can shift this warmer layer toward the surface and melt the bottom edge of the ice.
During the Great Arctic Cyclone (GAC) of 2012, a University of Washington Study found that a combination of churning and upwelling resulted in 60,000 square miles (150,000 square kilometers) of additional melt.Now that’s a huge chunk of ice taken out by just one storm.
The University of Washington Study noted:
… the ice melted largely from warm ocean water churned up by the passing storm. Melting quadrupled during the storm, and the rate of ice loss doubled, the study found.
In the Arctic summer, ocean water becomes stratified from melting ice, according to a statement from the University. A layer of ice-cold fresh water sits just beneath the sea ice. But about 65 feet (20 meters) below the surface, there is a layer of denser, saltier water that has been gradually warmed by the sun’s rays.
However, this cyclone was both stronger than the current one and it occurred during August, when the sun had two months more time to heat ocean waters below the ice. Further, it occurred in a region where ice was far more fragile. These factors all enhanced the GAC’s ability to impact sea ice.
2012-2013 Cyclones Reveal Fragile Ice
In the current cyclone what we have seen is a more general erosion of the central ice. Impact has been significant and this particular cyclone is doggedly persistent, continuing to chew away the ice over very long periods.
Cyclone-induced thinning appears to have happened primarily via dispersion and through upwelling impacts to the ice bottom. CICE, JAXA, and Uni Bremen confirm a continued thinning. Cloud cover has obscured most visual sensors this afternoon, however. So we will have to wait for another day or two before we can see down to the central ice surface to confirm what these other measures are telling us.
Nonetheless, we can still take a look at current and predicted thinning via the US Navy’s CICE measure below.
(Image source: CICE)
Note the barreling action of the low making doughnut-shaped impressions and leaving thinner ice in its wake. During the last series of frames, CICE shows the thickest ice just north of the Canadian Arctic Archipelago (CAA) taking a hit. Since the low is now in that region, we should be able to observe if CICE predictions continue to bear out.
A-Team over at the Arctic Ice Blog has also provided confirmation by putting together this animation of JAXA images to record ice thinning and divergence in the region:
(Image source: A-Team, Arctic Ice Blog, JAXA)
Note the rapid, counter-clockwise ice movement and expansion of cracks as the cyclone churns through the central Arctic.
Usually such impacts would not be so readily visible on the central ice. Some minor to moderate bottom thinning via cyclonic forces may have occurred in past years. The thicker ice of those years was better able to withstand such impacts. Further, the spreading of ice over larger portions of the Arctic tended to keep cold air in place longer, further reducing overall melt.
In this case, the extraordinarily thin condition of even the central ice enhances the impacts of all forces acting on it. So though these lows spread out the central ice, likely reducing the overall rate of edge melt, they do so at the cost of thinning the central ice, making it very vulnerable to melt as summer progresses. For this, somewhat early-season, storm to be showing enhanced thinning in the Arctic is yet one more visible proof of the ice pack’s fragility. And it is the primary reason we are talking about impacts to the central Arctic in early June and not impacts to traditional melt regions for this time of year like Hudson Bay.
Warm Air Pulse
A pulse of warm air following the storm pushed North Poll temperatures above freezing yesterday. Those higher temperatures currently remain in effect but are predicted to shift toward the Kara and Laptev Seas by tomorrow. This pulse has already enhanced ice thinning and melt near Svalbard. However, a layer of cloud riding over top of the warmer air has obscured much of the thicker ice.
You can see this column of cloud riding the warmer air in the Lance-Modis shot below.
(Image source: Lance-Modis)
In the wider shot, this kind of warm air and cloud influx can look a bit like a blow torch shooting up into the Arctic. If the air beneath the cloud is both warm and moist, it can have a similar effect on Arctic ice. Moist air carries more heat energy than dry air. So an influx of warm, moist air packs a bigger blow to the ice.
It’s an uncanny visual for a warm-air eruption caused by a fragmenting jet stream. You can view the wide-shot here.
Weather Forecast Shows Cyclone Hanging on Until June 14
ECMWF forecasts show the cyclone hanging on until at least June 14th. Should that happen, our cyclone, which Neven has dubbed the Small Arctic Cyclone of 2013 (SAC), will have lasted at least 20 days running. Some runs show the cyclone strengthening to 975 mb, just 9 mb short of the Great Arctic Cyclone of 2012. This would make the storm, at peak, a rather strong event, perhaps one worthy of a name upgrade to Persistent Arctic Cyclone of 2013 (PAC). And, if it ends up thinning the ice more than currently predicted it could end up becoming the Catastrophic Arctic Cyclone of 2013 (CAC).
We’re currently just witnessing thinning, not catastrophic thinning. So let’s hope it doesn’t come to that.
But since the forecast is for this storm to hang on for such a long time and to repeatedly move over regions of the central Arctic, we will have the opportunity to observe its impacts over the next two weeks. It is ample enough time to reduce much of the central ice to tiny fragments. A potentially very low resilience as the heat of July approaches.
The June 14 ECMWF forecast shows our cyclone as a double-barrel 995 mb low in the central Arctic north of the Kara and Laptev Seas, pulling warmer air over the Beaufort and CAA behind it.
(Image source: ECMWF)
We’ll keep a close watch on this storm. It’s not done by a long-shot and there may yet be a few surprises in store.
Just wanted to share this image of the strengthening Arctic cyclone. Note the tight, cloud-wrapped formation at the center. Most of the area is covered in clouds but, upper left, we see a network of cracks forming in the central ice.
(Image source: Lance-Modis)