Tuesday, 16 August 2016

Storm over thinning Arctic ice

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Powerful Cyclone to Blow Hole in Thinning Arctic Sea Ice

15 August, 2016
Back in 2012, a powerful Arctic cyclone smashed the sea ice with days of wind and powerful waves. This year, a storm that’s nearly as powerful threatens to make a similar mark on late-season melt. With a very unstable Arctic weather pattern in play, there’s an outlier possibility the dynamic is setting up for something even more dramatic by late August.
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Earlier today, a strong gale roared up out of the Laptev Sea north of central Siberia. Feeding on the abnormally warm, moist air over the Barents Sea and the hot air over northwestern Siberia, the storm collided with comparatively cold air over the central Arctic. The differences between hot/cold and damp/dry air can really bomb out a storm system.

Arctic Cyclone
(Storms, heat and moisture feed up through a high-amplitude wave in the Jet Stream over northern Europe and Siberia and into a developing Arctic cyclone over the Laptev Sea during the early hours of August 15, 2016. Image source: LANCE MODIS.)

Central pressures in the storm fell to 969 millibars and the winds whipping out over the Laptev, East Siberian, and central Arctic waters gusted at 45 to 55 miles per hour. Waves of 6 to 10 feet or higher roared through the newly-opened waters filled with increasingly dispersed ice floes.

The Great Arctic Cyclone of 2016?

This powerful storm is pulling these strong winds over some of the weakest and thinnest sections of Arctic sea ice. During July and August a huge section of ice running along the 80° North Latitude line and stretching from the Laptev, through the East Siberian Sea, and into the Beaufort Sea grew ever more thin and eventually dispersed. Now 25 to 60 percent ice concentrations in this region abound — a tongue of thinning which stretches nearly to the North Pole itself.
Powerful Arctic Cyclone
(A powerful storm running out of the Laptev Sea and into the central Arctic is threatening sea ice with strong winds, large waves, and the motion of abnormally warm surface waters. Image source: Earth Nullschool.)

The storm is generating waves, mixing warmer-than-normal surface waters with even higher temperature waters just below. These sea surfaces are between 1 and 2 degrees Celsius above average over much of the area, with pockets of 3 or even 4 C above normal surface water temperatures interspersed. The storm’s Coriolis Effect will spin chunks of ice out from the pack to float lonely in these warmer-than-normal waters as they are churned by the raging swells.
Storm Raging Over Warm Waters, Thin Ice

Currently, the storm’s strongest winds and waves are running through a big melt wedge that extends from the Laptev and East Siberian Seas toward the 85th parallel. The motion and force produced by the storm’s winds and waves will eject the ice currently located over the northern East Siberian and Chukchi Seas even as waves eat into it. Upwelling of warm water in the seas beneath the center of the storm will open and disperse the ice, generating holes and polynya as it tracks north of the 85th parallel and toward the Pole.
Thin Arctic Sea Ice
(Very low concentrations of ice, like those seen in this Uni Bremen image, are vulnerable to disruption and melting by storms during August and early September. Current ice thinning and dispersal are among the worst seen for any year. With a powerful storm now raging over the ice, impacts to end-season totals could be significant. Image source: Universität Bremen.)

Compared to the Great Arctic Cyclone (GAC) of 2012 — an event that helped to tip that year into the strongest late-season melt on record — this storm is a bit weaker. The GAC bottomed out at 963 mb and carried on for about four days. The current storm, by comparison, is expected to remain in place for quite some time even as it slowly weakens over the coming days.

Arctic sea-ice extent values are now tracking at around third lowest on record, or just above the 2007 line. Such a strong storm certainly has the potential to knock a big hole in the ice, possibly propelling 2016 closer to 2007 ranges or even beyond them. Surface waters in the Laptev, East Siberian, Chukchi, and Beaufort Seas aren’t quite as warm as they were in 2012, but there’s still a lot of potential here for storm-associated melt. Meanwhile, the very warm waters over the Kara and Barents Seas remain a disturbing feature.

Arctic in hot water
(Above-average sea-surface temperatures during late summer have more potential to rapidly melt sea ice when they are churned up and put into motion by powerful storms. Image source: NOAA NCEP.)

Models predict that lows will continue to feed in from the Atlantic and northeastern Siberia along various high-amplitude waves in the Jet Stream to combine in a triangular bite between the East Siberian Sea, the Laptev Sea and the Pole. Such continued reinvigoration will tend to enforce a generally stormy and unstable atmosphere. And there’s some risk (small, but worth considering) that the current storm could refire into something more powerful on the fuel provided by one of these lows.
Troubling Atmospheric Instability Loads the Dice for Future Bombification
Already, a few of the long-range models are popping with amazing predictions of storm-center intensity in the range of 950 to 960 mb. Both the GFS model and CMC models separately produced these results for the nine to 12 day timeframe. GFS had backed off its own high-intensity forecast when this odd CMC run popped up (see below).
CMC Arctic Megacyclone
(CMC 10-day forecast model run showing an extremely powerful 955-mb low just north of Svalbard on August 25th. Such a storm is low-probability at this time, but its formation would likely result in serious impacts to sea ice. Image source: Tropical Tidbits.)

Though these are long-range outliers, there is quite a lot of fuel for strong storms in the region this year due to conditions related to human-caused climate change. In particular, ocean surfaces in the Barents and Kara Seas are in record-hot ranges. And the heat and moisture coming off those waters is fuel for some serious atmospheric instability as the Polar region attempts to cool. Any significant cooling in the 80-90° North Latitude region would help to generate a strong dipole between this zone and the Kara-Barents. Such a dipole would create strong instability for storm generation.
A low bombing out at 953 to 955 mb in ten days, as the CMC model currently indicates, would represent an Arctic megacyclone with serious potential to wreck sea ice. The location predicted would generate a strong push of warm water from the Barents and Laptev and on toward the ice-clogged polar waters. The resulting Ekman pumping and powerful swell generation would have the potential to generate severe ice losses in the late August timeframe.

Probabilities for such a storm this far out are low, but given the underlying conditions, it’s worth putting a marker out. This is, therefore, a situation to watch. We’ve already got one strong storm blowing away at the ice. A one-two punch would hurt even more. In other words, the situation in the Arctic just got really interesting. Let’s just hope it doesn’t tilt into scary…
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