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| Well fuck. |
It turns out that the circumpolar whirl over the Arctic is elliptical and hence has two nodes. One normally lies over Baffin Island; the other, northeastern Siberia (Yakutia? Chukotka?). This is contrasted with Antarctica's polar vortex, which is stabler with only one node over the Ross Ice Shelf; the best guess for why that is, is because the Southern Hemisphere has a landmass at the pole, and the Northern, an ocean.
The thing about an ellipse, though, is that it is less stable than a circle. Right now the Antarctic whirl looks to be between Ross and Graham Land. But look at that deep burgundy in Siberia!
Hypothesis time: Warm air is pushing the Siberian node of the Arctic whirl into the ocean; this in turn is displacing the Baffin Island node into eastern continental North America.
Hypothesis #2: The greater variability of the Arctic whirl (relative to the Antarctic's) has something to do with the ice age cycle of the past five million years. It is notable, for example, that the southernmost extent of the recent polar vortex broadly parallels, in latitude, the southernmost extent of glaciation historically associated with ice ages.
...And #3: Perhaps the proximate cause of the ice age cycle is the destabilization of the Arctic whirl? But if that is the case, what catalyzes it?
Thought it might be relevant to your musing on ice age climate:
ReplyDelete"Siberia enjoys a well-deserved reputation as one of the coldest places on Earth. But the last time the planet got really cold, Siberia apparently didn't go along for the ride, providing animals a warm oasis from the Ice Age.
That's the finding of Eva Bellemain of the University of Oslo, who recently presented her analysis of DNA found in the Siberian permafrost that dates back 15,000 to 20,000 years ago. During that time, much of the northern hemisphere was engulfed in massive glaciers, but it appears this part of Siberia escaped this, instead becoming a refuge for wildlife."
http://io9.com/5874997/siberia-was-an-unlikely-haven-for-wildlife-in-the-last-ice-age
That's fascinating. Check out this map: it appears that if you consider the extent of Ice Age glaciation as (roughly) circular*, then Greenland consistently sits in its center. That is, Greenland is home to the Northern Hemisphere's permanent cap.
ReplyDeleteAnother interesting element is that, for the past several million years, ice age has been the dominant climatological pattern of the Northern Hemisphere, and that ice ages have come and gone in a remarkably steady cycle--one that is, as yet, unexplained. But something able to power such a cycle over such a long period of time must be very strong indeed...
A guess? The circumpolar whirl, being elliptical, sweeps around the hemisphere slowly; warm periods occur when both nodes are furtherest from the Greenland ice cap; ice age begins as one of the whirl's nodes sweeps onto the cap and erodes as it passes out over Iceland and Scandinavia, triggering another warm period...But wouldn't such a pattern yield a 50/50 ice age/warm period split rather than the 80/20 one we now observe?
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*Actually, it's elliptical.
It appears that Greenland remained glaciated, in spite of the near-total melt of the Laurentide ice sheet (much of which was at the same latitude), because of its naturally mountainous topography. This also seems to explain the continuing glaciation in Ellesmere and Baffin Islands. The ice cap itself makes Greenland by far the highest land mass in the Northern Hemisphere:
ReplyDeletehttp://all-geo.org/metageologist/wp-content/uploads/2012/01/Elevation.jpg
The presence of Greenland may be helping to destabilize the vortex, contributing to the elliptical shape that makes it prone to fluctuation. The issue I have is that the major factor in initiating glaciation is not winter temperatures, but summer temperatures. The snowpack must survive more or less intact into the fall. However, the temperatures where the Laurentide sheet supposedly originated are today much too warm in the summer months to keep snow on the ground much past May (Kuujjuac in far northern Quebec reaches into the 60s F during July and August). Resolute, north of Baffin Island, has summer temperatures in the low 40s, and seems to keep some large patches of snow on the ground at least until August:
http://en.wikipedia.org/wiki/File:Resolute_Bay_1_1997-08-02.jpg
For glaciation to commence again in northern Quebec and Nunavut, you'd need dramatically lower summertime temperatures, but can the vortex supply those? It operates in the summer, but is supposedly much weaker. I agree, though, that the vortex as it appears now seems to mimic the location and extent of the old ice sheet (noting also that Alaska was partly unglaciated during the ice age according to your map, and there was at some point a corridor of ice-free land running from Alaska to the lower 48):
http://robertscribbler.wordpress.com/2014/01/23/arctic-heat-wave-to-rip-polar-vortex-in-half-shatter-alaskas-all-time-record-high-for-january/
Let me add, by the way, how messy Resolute Bay looks like. Like a child that just threw his toys everywhere on the floor. No pattern whatsoever.
DeleteI dunno about Greenland having quite that much of an effect. It's not so different from the Antarctic Peninsula. My guess is that the root cause of the northern vortex's volatility is the Arctic Ocean itself; note the transposition of land v. water patterns in the Northern Hemisphere vs. the Southern.
ReplyDeleteWhat I really find interesting is how cyclical the Ice Ages themselves are. This implies that their primary catalyst must itself be regular and periodic...
Isn't that what makes the orbital cycle theory (i.e. the Milankovitch Cycles), despite some unresolved issues, the most compelling explanation? It's really the only mechanism that can supply such consistent regularity over very long time spans. The mechanism does seem to be precisely cooling summers and warming winters:
Delete"When the obliquity (the angle of Earth's axial tilt) increases, the amplitude of the seasonal cycle in insolation increases, with summers in both hemispheres receiving more radiative flux from the Sun, and winters less. Conversely, when the obliquity decreases, summers receive less insolation and winters more.
But these changes of opposite sign in summer and winter are not of the same magnitude everywhere on the Earth's surface. At high latitude the annual mean insolation increases with increasing obliquity, while lower latitudes experience a reduction in insolation. Cooler summers are suspected of encouraging the onset of an ice age by melting less of the previous winter's precipitation. Because most of the planet's snow and ice lies at high latitude, it can be argued that lower obliquity favors ice ages for two reasons: the reduction in overall summer insolation and the additional reduction in mean insolation at high latitude."
FWIW, note that Siberian Russia has higher summer temperatures than Arctic Canada (Yakutsk is in the 70s from June to August, compared to the 60s for Yellowknife). Kuujjuac is much colder still. The origin points for the ice sheet seem to be right around Hudson Bay, where summertime temperatures are heavily moderated by that ice-cold body of water. The same applies, to a lesser degree, for the area around the Baltic.
And yes, these polar settlements/bases tend to have a very messy, disorganized appearance:
http://www.scottkessel.com/wp-content/uploads/2009/06/McMurdo.JPG
Although the "street network" such as it is, is organic:
http://upload.wikimedia.org/wikipedia/commons/1/17/Mcmurdo118.jpg
I agree that the Milankovitch theory is the most convincing explanation (though enough problems remain--especially w/r/t effects appearing before orbital forcing would predict them to--to not make it quite compelling...yet). The only other explanation that could even make sense would be that we're looking at a wholly emergent phenomenon, but even then (a) emergent patterns tend to be significantly more chaotic, and (b) why would it match up so well with the Milankovitch cycle?
DeleteWhat I found particularly interesting was the Rosby wave article you linked to earlier. The sum effect of the wave producing an enduring ridge over Alaska and a trough over continental North America has been to shift the circumpolar vortex's Baffin Island node down into a much lower latitude.
I wonder--even if forcing is an important part of the ice age cycle, is it its ultimate catalyst? And if not, what is? Since the function of the circumpolar system is to keep the cold in, wouldn't its southward migration result in a concentration of polar cold much further south (just like what we've been seeing)?
I find myself suspecting more and more that part of the ice age cycle is a speedup and slowdown of the jet stream. The ice age would then be precipitated by a slowdown causing large, permanent Rosby formations to form, locking arctic air in a region much further south than the poles, while circulating warm air deep into the polar regions. As such a system stabilizes, pack ice forms in major bodies of water (the Hudson Bay for us, the North and (especially) Baltic for Europe), growing into glaciers and then sheets under unyielding cold...But even then, this explanation has weaknesses. Most importantly: Why is Siberia so persistently ice-free? Perhaps the answer is that the permanent Rosby system doesn't randomly propagate, but is rather fueled by warm air from the Pacific basin, which cleaves the polar vortex precisely in such a way that arctic focus migrates downward into continental Europe and North America. Siberia, by contrast, has no warm source of such clear strength, and so its portion of the circumpolar storm isn't locked into place the way its American counterpart is ... unless, that is, the cleaving action involves its own forcing -- Remember when I noted that the ice age sheets are themselves elliptical? I wonder if part of ice ages' formative processes is that one half of the polar vortex is locked over the Hudson Bay, and the other half the Baltic Sea? That would imply that the deep warm-air wedge from the Pacific into the Arctic basin has the effect of pushing the eastern hemisphere half of the whirl in front of it ... and that the ice age itself is catalyzed when it's pushed as far up as it can go, i.e. the Baltic Basin, the furtherest point in the Arctic basin from the Bering.