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The Big Thin Begins: Week-Long Cyclone Chews Away Fragile Arctic Sea Ice

cyclone-arcticictn_nowcast_anim30d

(Image Source: CICE)

A moderate-strength cyclone that emerged about six days ago and is expected to last at least until Monday is slowly chewing away a large area of Arctic sea ice near the North Pole. Cyclonic action generated by the storm is now resulting in an unprecedented thinning of central Arctic sea ice. It is important to note that should this ice thinning continue, it could have major impacts on end summer sea ice this year.

The low that is causing the trouble moved out of the region of the Beaufort Sea, skirted East Siberia and had transitioned into the central Arctic Ocean by about May 24th. Since then, it has persisted, remaining nearly stationary with a slow drift back toward the Beaufort. Forecast maps show the low remaining in this region until at least Monday before it weakens and moves toward the Mackenzie Delta. Strangely, long-rage forecasts show it re-strengthening even as it returns to the central Arctic.

Arctic cyclone

(Image source: DMI)

Minimum central pressure continues to hover around 990 millibars. This moderate strength compares to the much stronger Great Arctic Cyclone of 2012 which bottomed out around 960 millibars. However, the storm is quite strong for this time of year, when Arctic cyclones tend to be rare and weak, containing enough energy to generate winds that erode sea ice.

This erosion takes place via a pumping process by which the ice is pushed against the ocean surface by the cyclonic wind field. This motion, in turn, stirs up the underlying waters creating a warm, upwelling current. Since the forces occur over broad regions, powerful surface forces allow the upwelling to dredge deep, causing mixing between surface and lower layers. Tendrils and micro-currents of warmer water thus rise to contact the ice. This action can melt the sea ice from below, breaking it into smaller chunks, opening polynas, and riddling the ice with leads. If the storm grows strong enough, large wave action can devour whole sections of ice. But, in this case, the storm does not appear to be powerful enough to generate this kind of wave action.

Since 2012, we have already seen two major upwelling events. One, already mentioned, was the Great Arctic Cyclone of 2012. The second, involved strong off-shore winds during February and March which pushed ice away from shore and, in the region of Barrow Alaska, resulted in near-shore upwelling that temporarily melted ice even as it was pushed out to sea. The combined result was open water during winter.

We can see the storm’s current and projected impacts on the CICE model run posted at the top. CICE is projecting the development of a large area of thin and fractured ice near the North Pole in the storm’s wake even as a region of thick ice north of the Canadian Arctic Archipelago erodes. These projections show average thickness in a wide region falling from about two meters to less than one meter.

That’s very thin ice for North Pole regional waters.

Already, some impacts from the storm are visible in Lance-Modis shots of the region.

Arctic_r04c04.2013150.terra.1km

(Image source: Lance-Modis)

In the above shot, we can see the center of our moderate-strength cyclone near the middle-left portion of the image. To the right of the storm center, we can see down through the clouds to areas where the ice has fractured, revealing the dark blue waters beneath. Below the storm center and near the lower left-hand corner of the image is the North Pole. So what we are seeing is a broad area of leads and fractured ice with gaps measuring up to about 5 km wide within 200 miles of the North Pole. This kind of development is not at all usual for late May, much less late August.

CICE model runs show ice in this region continuing to thin, fracture and weaken as the storm passes.

As the storm moves away, it is expected to pull warm air in behind it, which could further weaken the ice. ECMWF weather forecasts show this warm air influx occurring by about June 4:

WarmairRecmnh1202

(Image source: ECMWF)

In the above image, we see 5 degree C temperatures plunging directly into the heart of the Arctic. A powerful late spring event should it emerge.

In the past, storms of this kind have had very little impact on sea ice. However, this year the ice is very thin and spread out. Most ice in the Arctic is showing a thickness of two meters or less. Records of past melt seasons show that two meter or thinner ice is unlikely to survive the melt season.

Furthermore, packs of much warmer air are drawn closer to the Arctic center by a wavy pattern in the jet stream. The result is that large north-south swoops draw warmer air up from the south even as they push Arctic air into more southerly regions. Europe, in particular, suffered due to this mangling of the jet stream. Ironically, a growing body of scientific evidence shows that these very changes in the jet stream are a result of loss of sea ice. So it appears that loss of sea ice is resulting in a snow-balling of forces that contribute to its ultimate demise.

The ultimate result is an Arctic-wide ice thinning impacting even the most central and protected areas. Even in this region of the central Arctic, where ice is usually much thicker, large regions of 2 meter or thinner ice dominate. You have to venture closer to Greenland and the Canadian Arctic Archipelago to find areas of ice thicker than 2 meters. However, as the recent evacuation of a Russian Arctic Expedition in that region shows, even the thickest ice is far more fragile than before.

The result of all this thin and broken ice is that it is much more vulnerable to surface conditions. A storm moving over thin and broken ice is much more likely to churn it up, breaking it and mixing it with the warmer waters underneath. Last year, we saw this process in action during the powerful Great Arctic Cyclone which emerged in August, churning up a large area of the Beaufort Sea, then drawing warm air in behind it, resulting in major sea ice losses.

At times when ice was thicker, moderate or powerful storms would not pose a threat for enhanced melt. But since 1979, the Arctic has suffered an 80% loss of sea ice volume.

This year, sea ice volume is currently at record low levels. Yet the ice pack is very spread out, boasting an area near 2002 values. This combination of wide coverage and low volume leaves the ice very, very thin and fragile. So now, even moderate cyclones like the one hovering near the North Pole can chew away at the ice.

If the CICE projections bear out, we’ll see the central ice pack greatly weakened in the wake of this storm just as solar radiance and warm air build into mid-June. At this point, such injuries to the ice make it more likely that rapid and catastrophic decline in coverage will begin to dramatically ramp up over the next few weeks.

As Neven over at the Arctic Ice Blog notes:

I feel the Arctic sea ice pack could soon go POP under the right conditions.

Let’s see:

  1. Thin, spread-out ice pack.
  2. Persistent storm chewing away the central ice.
  3. Large cracks and areas of open water riddling most of the ice pack.
  4. Large polynas forming behind the ice edge.
  5. Upwelling events eroding the bottom ice.
  6. Loss of Arctic expeditions in the region of the ‘thickest’ ice.
  7. June heat and constant, direct sunlight approaches.

Looks to me like a lot of the ‘right’ conditions are present.

In short, don’t let the high extent and area numbers fool you. The thin, spread out state of the ice leaves it more vulnerable, not less so. The sea ice is weaker and less resilient than it ever was. Only a cold summer and conditions favorable for ice retention are likely to prevent a record melt in either area, volume or extent. On the other hand, very bad conditions could result in near-total melt (under 1 million square kilometers end season area).

UPDATE:

Long-range weather models show the cyclone sweeping down toward the Mackenzie Delta, drifting back toward the Canadian Arctic Archipelago and finally returning to the Central Arctic by mid-June. Such a prolonged storm event would likely have a continuous weakening affect on the ice. Lower temperatures in the storm’s region would be more than countered by active wave energy and tapping of warmer, deeper waters which will have a tendency to erode the ice from beneath. Furthermore, warmer air is shown to follow in the wake of this storm, which may enhance melt through regions of already weakened ice.

In any case, this is a situation that bears close watching. A month-long, or more, storm harrying the Arctic could have quite an impact.

ECMWF weather model forecast for June 9th:

Cyclone june 9

(Image source: ECMWF)

Links:

CICE

DMI

Lance-Modis

The Arctic Ice Blog

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