I would assume there are certain pathways and weather anomalies tied to continental and ocean currents configuration, thus preferred position appear to me very likely. I would think that because it is difficult to evaluate the AMOC/THC for instance conclusions are a challenge. Btw, Screen published a study in 2013 and found a stastitical significance… Influence of Arctic sea ice on European summer precipitation
“Here we show that months of extreme weather over mid-latitudes are commonly accompanied by significantly amplified quasi-stationary mid-tropospheric planetary waves. … Depending on geographical region, certain types of extreme weather (for example, hot, cold, wet, dry) are more strongly related to wave amplitude changes than others.”
Thank you for pointing out this research and describing it clearly. And thanks to you and your group for leadership in investigating large scale circulation and extreme weather.
Now all you have to do is snap your fingers and make me understand inertial waves.
It’s good to know that we’re finally getting down to the level of detail about this issue which will help with adaptation. Of course we’re not there yet, but the latest research seems to be a giant step in the right direction.
” A cool mass of air heads toward the United States from the upper regions of Canada and Alaska this week, according to the National Weather Service.
ABC News’ Ginger Zee says the weather pattern is not an actual polar vortex, though.”
“Francis and Vavrus (GRL 2012) argued that a reduction of the north-south temperature gradient would cause weaker zonal winds (winds blowing west to east) and therefore a slower eastward propagation of Rossby waves.”
Maybe I am getting this backwards, but shouldn’t polar amplification increase the north-south temperature gradient, rather than reducing it?
I thought there were some problems with the Barnes paper. It it really the case that there have been no changes in Rossby waves. Can we really not attribute any of the ‘stuck’ patterns that we have been seeing so far to greater amplitude of Rossby waves? If not, then what _is_ causing these increasingly stalled weather patterns?
The poles are colder that the equator. If the poles warm faster, then the difference in temperature between the poles and the equator is reduced which means the gradient is reduced. So far, this seems to only affect the North pole.
Re Wili, i think the Barnes study points out that Arctic amplification can not explain trends in midlatitude weather patterns, alone. Though, the study found a significant decrease in the month October-November-December, and concludes – but this trend is sensitive to the analysis parameters. Not entirely sure what that means but i guess, more studies are needed.
This video seems to be relevant, when Trenberth made similar points.
There were no ‘problems’ with the Barnes paper. Dr Barnes was correct.
Francis & Vavrus 2012 didn’t manage to show what they claimed to show. What Screen & Simmonds have managed to do is identify what F&V2012 didn’t.
Barnes never said the effect wasn’t happening. She concluded that “the wave elongation reported by FV12 is at least partially an artifact of the poleward shift of the isopleths with polar warming.” Screen and Simmonds 2013 also showed that F&V2012’s method was picking up artefacts of their method.
Barnes concluded: “The Arctic is changing rapidly, and these changes will likely have profound effects on the Northern Hemisphere. This study, however, highlights that the relationship between Arctic Amplification and midlatitude weather is complex.” Which cannot be read as a dismissal of the premise F&V2012 were studying.
I’m sure that I’m confused here, but since the aim of the paper is partly to make some contact with the Francis et al. hypothesis, wouldn’t the appropriate wave amplitude metric to examine be the meridional extent of selected isopleths at, say, the 500 hPa level (or higher, see below)? The paper examines reanalysis output of height anomalies averaged over a fairly broad swath across the mid-latitudes and selected regions, whose relevance is a bit less intuitive for me with respect to what Dr. Francis and others are postulating.
Just my $0.02 for discussion purposes, but there are still a lot of dynamical mysteries relating to the issue of Arctic sea ice/mid-latitude weather variability. For example, the decreased pole-to-equator temperature gradient discussed in the post is primarily expressed close to the surface (and manifested seasonally), whereas the opposite situation is true near the tropopause (where the upper tropical troposphere warms up much more than the polar tropopause regions). It’s not obvious, to me at least, why the mechanisms controlling the lower layer thickness anomalies should win out when talking about wave propagation along the Polar jet. The dynamical trends in the Southern Hemisphere, for example, seem strongly linked to ozone trends that are occurring much higher up in the atmosphere. Moreover, although the vertical gradient in east-west wind is slaved to the pole-to-equator temperature gradient in order to obey the thermal wind balance, the vertical gradient in north-sound wind depends on east-west temperature gradients, which could be important when thinking about regional and basin-by-basin trends.
If the underlying mechanisms were “simple” in that they were elegantly connected only to low level temperature gradients, CMIP5 should have no problem simulating with trends in the prevailing wave propagation characteristics.
Since the observations and simulations of propagation changes are equivocal, the underpinning theory not well-established, and the whole hypothesis focuses on the wintertime mid-latitudes (that exhibits very large unforced temperature variability), any dialogue about climate-wintertime weather connections should probably keep in mind the closing sentences from the Wallace et al. letter in Science here : “…But to make it the centerpiece of the public discourse on global warming is inappropriate and a distraction. Even in a warming climate, we could experience an extraordinary run of cold winters, but harsher winters in future decades are not among the most likely nor the most serious consequences of global warming.”
From the “why didn’t I think of that” department, the fact that this obvious relationship between high-amplitude waves and extreme weather wasn’t yet documented statistically makes for the easiest paper project ever. It’s like 101-type stuff. Kudos to them for seizing the opportunity.
However, and I think this RC post also alludes, I’m left quite wanting on how little ‘implications’ the research leaves us with. I realize it may not have been the focus of the paper, but ‘everybody’ wants to know what exactly is going to be the result of greater differential Arctic warming. Will it be weaker/zonal waves, or “high amplitude quasi-stationary” waves?
But, while we’re on the subject of intuitiveness– isn’t it hard to make a case for “high amplitude” quasi stationary waves? I mean, they rarely are stationary, with the exception of cut-off lows, and with those there’s much less room for ‘extreme’ weather seeing as they often modify in terms of temperature and don’t provide adequate breeding grounds for tornadoes nor hurricanes (at least on the trough side).
And, when viewed in another light, doesn’t this research continue to cast a pall on those who wish to insta-denigrate those who would suggest that ‘The Science’ might be unsettled toward conclusive statements on future Tornado/Hurricane climatology..?
Thanks prok and Chris R for those illuminations. I would also love to see Chris C excellent points at #16 addressed. My first guess is that it is the great amount of warming in the lower Arctic lower atmosphere that changes the height along which the jet stream flows. Temperatures gradients higher in the atmosphere would have less of an effect, I would think. (But, need I add, I’m no expert.)
Does Prof. Frances’ model work for the southern hemisphere? My impression is that it is specifically oriented toward the northern hemisphere. I hear that NZ is currently experiencing a rather extreme ‘stuck’ pattern. If such stuck patterns are also increasing in the southern hemisphere, don’t we need another mechanism to explain it than we do for the northern hemisphere?
…Stupid question: IIRC, average atmospheric humidity has risen by about 6%. Wouldn’t that have an effect on how everything in the system behaves? Could this be part of the explanation for increasingly ‘stuck’ systems? In other words, do heavier systems (laden as they are with more water vapor) tend to move more slowly?
Wii (22): “Do heavier systems (laden as they are with more water vapor) tend to move more slowly?” – thye would be heavier only if the air mass is “ladden” with water droplets. If water vapour remains as water vapour, i.e. as gas – then the air with more water vapour is LIGHTER- the average molecular mass of water molecule is 18, while the average weight of molecule of air should be around 28. But then again if the other air mass is also more humid these increases in humidity would at least partly cancel each out as it is the relative difference in density that matters.
Maybe it’s just me but there seems something wrong with the tendency over many years for surface thermal surface lows to form cyclonic “rotten centers” beneath subtropical Rossby ridges. The idea has always been that these ridges are salients of tropical air moving northward aloft and they are supposed to be cooling and sinking. So how in this regime do you get monsoonal moisture and warm sea surface anomalies moving north as is happening right now off California?
The obvious answer is that all that sunshine bakes the surface so much that convecting air overmatches the sinking pressure and forces the subsidence to the edges. That notion works pretty well over land which is where monsoons are supposed to be, but the current rascal is offshore and it is a tongue rather than a circular cyclone and its moisture is being entrained in the macro anticyclonic flow and flung eastward across the Klamaths and the Rockies.
Also just checking to see if perchance the Berlin Wall has come down.
> water vapor is actually _less_ dense than dry air.
Fun facts from physics: the Wright Brothers made that discovery — after flying at the wintertime North Carolina beach, they packed up and went home. The next summer in Ohio, their aircraft didn’t fly. They figured it out.
This notion of an equator-to-pole Hadley cell is quite implausible in my mind for a planet exhibiting Earth-like rotation rates. Such a state would require enormous angular momentum dissipation of the upper-level flow; in the current climate, twin constraints of near angular momentum conservation and the thermal wind equation demand latitudinal confinement of the circulation. You don’t need to appeal very much to the baroclinic instability that occurs in the mid-latitudes to arrive at this conclusion, even if it’s a critical part of Hadley cell termination in the real world. There are more compelling ways to start thinking about equable climate dynamics, but I don’t view any of this as particularly relevant for the “small” amounts of global warming we’re talking about in the 21st century.
I wouldn’t have thought so, since the Southern sea ice isn’t crashing, and Antarctic warming is (barring the peninsula) mostly still small enough to be hard to detect. Therefore the preconditions for the posited effect don’t exist in the Southern Hemisphere–despite the situation in NZ that you refer to.
A standard pilot’s phrase for reduced aircraft performance is “high. hot, and humid”. They refer to high altitude, hot temperatures, and high humidity, all of which lead to lower air density. Lower air density means less lift from the wings.
The 1940’s seem to have experienced a similar period of arctic amplification. Given that many of the regions covered by this work will have fairly good data in this period, is it possible to see similar processes back then?
“Bob Loblaw says:
17 Jul 2014 at 6:38 PM
Yet more fun facts from flying:
A standard pilot’s phrase for reduced aircraft performance is “high. hot, and humid”. They refer to high altitude, hot temperatures, and high humidity, all of which lead to lower air density. Lower air density means less lift from the wings.”
In prop aircraft it also means less thrust from the prop for the same reason.
I recall after a summer of flying lessons flying on a frosty morning and wondering what they had done to the engine! The takeoff distance was shorter and the climb out rate was impressive compared with earlier in the year.
Yes, you’re right. A prop gets its pulling power from the same “lift’ mechanism that a wing does.
I did my flying training in Ottawa, close to sea level, mostly in winter. I was used to getting off the ground in about half a 2000′ runway. When I moved to Calgary (4000′ ASL) and started flying in summer, I wondered if I was going to get off the ground before I ran out of space on a 4000′ long runway…
Facts nicely handled and integrated into Peter Heller’s The Dog Stars, which is in part a climate change novel (though his Apocalypse–yes, its a post-Apocalypse novel–is mostly due to super-flu.) There’s a scene in which the protagonist has to get his vintage Cessna out of an extremely tight place… though from this review you’d never know what a large part of the story flying is:
The aircraft lift stuff is fascinating. Johannesburg, South Africa is a relatively high-altitude airport and I remember the odd time feeling that the poor 747 was battling to get of the ground. The place has extremely dry (though not super-cold) winters, so I should remember to plan my future departures from there for winter :)
Thanks once again to RC for making new research accessible.
The Antarctic has the recurring ozone hole which is a much more pronounced and regular feature of that region than anything in the way of ozone depletion that happens in the Arctic. One net effect is a reduction of ozone all year compared to the north. Ozone strongly absorbs radiation. The ocean surrounding Antarctica allows the most powerful ocean current and powerful winds to in comparison to the Arctic, isolate Antarctica. People would need to keep things like this in mind when wondering why “polar amplification” doesn’t affect both poles equally.
I think if someone were to monitor the changes on the PNW coast here in Tofino British Columbia Canada…on Vancouver Island’s west coast…over the last two years..With the jet stream much further north, warmer night time lows, the reduced wind events off the ocean, the much warmer ocean water( surfers are wearing summer suits much, much sooner now)…the fact that we are not getting the wet fog events…and record breaking temperatures all year 2014…but mostly there is no wind..no heavy rains..no storms. Now I’ve only lived here twenty years, and out here we all watch the weather cause there’s usually so much of it…and our industries are dependent on the weather…well, it’s pretty darn strange. Might be due to these wind events…
“Trapped atmospheric waves triggered more weather extremes”
Weather extremes in the summer – such as the record heat wave in the United States that hit corn farmers and worsened wildfires in 2012 – have reached an exceptional number in the last ten years.
Man-made global warming can explain a gradual increase in periods of severe heat, but the observed change in the magnitude and duration of some events is not so easily explained. It has been linked to a recently discovered mechanism: the trapping of giant waves in the atmosphere.
A new data analysis now shows that such wave-trapping events are indeed on the rise.