Saturday, 3 September 2016

Warm conditions in Antarctica

Warm, Storm-Force Winds Blowing From the Equator Flip West Antarctic Winter to Summer

2 August, 2016
In a record-hot world, there’s a lot of lower-latitude heat just waiting for a weakness in the increasingly feeble Jet Stream to make a big poleward rush. Such was the case today as an intense wave of warmth exploded up from the Equatorial region and began to spread summertime temperatures over sections of West Antarctica — technically still in the grips of the Southern Hemisphere’s winter season.
image
(A surge of heat breaks over West Antarctica on September 2nd, 2016, pushing air temperatures over vulnerable coastal glaciers and ice shelves near or above the melting point [0 degrees Celsius]. Image source: Earth Nullschool.)

The warm winds began their southward turn about a thousand miles west of coastal South American and along the 20 degrees south latitude line. Tapping hot, tropical air, the winds then ran over hundreds of miles of open ocean — following the arch of a bulging ridge in the Jet Stream. These winds then gathered, howling through the Southern Ocean with storm force gusts of 50 to 65 mph before delivering their payload of abnormal warmth to West Antarctica.
Larsen C Ice Shelf Experiencing Above-Freezing Temperatures in Winter

Along the coast of Ellsworth Land, temperatures have risen to near the thawing point (0 degrees C), in winter, in a region that typically sees -2 to -3 C readings during summer. Temperatures that are 15 to 23 C above average (27 to 40 F) now range all over the Antarctic Peninsula and nearby areas of West Antarctica. Perhaps most dramatic are the 1.5 C readings coming from sections of the C region of the Larsen Ice Shelf bordering the Weddell Sea. There, downslope hurricane-force winds howling over the shelf are helping to spike local temperatures even as sea ice in the Weddell is splintered and shoved away from the Larsen C edge.
West Antarctic Heatwave
(A wave of 20+ C [36+ F] above-average temperatures blankets the vulnerable glaciers of West Antarctica on Friday, September 2nd. This pulse of tropical warmth is enough to drive readings over Antarctica to summertime or warmer ranges during winter, with some regions that typically experience below-freezing temperatures year-round nearing or exceeding the thawing point. Image source: Climate Reanalyzer.)


Larsen C is of particular interest due to a large crack spreading through its main body,threatening to break off a Connecticut-sized chunk of ice and disrupt the stability of the larger ice shelf. The most northerly of the remaining large Antarctic Peninsula ice shelves, this towering mass of frozen water serves to buttress a number of large Antarctic glaciers. Its loss or destabilization would allow these glaciers to increase their speed of ocean discharge and in turn, speed the rate of global sea-level rise. Needless to say, this combination of above-freezing temperatures during winter and hurricane-force winds won’t help to stabilizethis now more than 120-kilometer long and hundreds-of-feet-deep crack.

Antarctic_surface_temperature
(Differences between average summer and winter temperatures over Antarctica. For sections of West Antarctica near the Antarctic Peninsula, Friday through Sunday will see temperatures more typical to Antarctic summer — during late winter. Image source:European Center for Medium-Range Weather Forecasts.)

A Winter of West Antarctic Heat — Larger South Pole Warm-up on the Way?

More broadly, warming this region to above freezing for extended periods is a concern among glaciologists. In the past (during the Pliocene and Miocene), when atmospheric CO2 levels have hit a range of 390-405 parts per million or above, West Antarctica (and ultimately East Antarctica) experienced warmth which resulted in seas that were many feet and meters higher than today. With atmospheric CO2 readings likely to average near 405 ppm during 2016 (or total greenhouse gas levels in the range of 490 ppm CO2e), it appears that frequent periods of summer-like temperatures and related increasing melt pressure are now possible during polar winter.
Over recent months, this section of Antarctica has been clobbered repeatedly by such spates of above-normal temperatures. Back in June, an odd Jet Stream excursion (gravity wave) pulled a big pulse of Equatorial heat over West Antarctica. Today’s event is just one of a number of recent big warm air invasions into this highly vulnerable zone.
CFSv2 Hot South Pole Summer
(More severe melt stress for Antarctic glaciers? NOAA’s CFSv2 model shows a ridiculously hot South Pole summer may be on the way. Side note — over the past year or so this forecast model has run somewhat cooler than actual temperatures for the Arctic region. Image source: NOAA.)

Taking this most recent warming event into context and looking forward into late 2016 and early 2017, at least one global forecast model is predicting a period of severe Antarctic warming during this time. NOAA’s CFSv2 model, for example, finds a very extreme Antarctic temperature spike emerging over pretty much all of Antarctica during the late Southern Hemisphere summer and early fall months of 2017.
Links:

Weather data provided by the Global Forecast System Mode


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