# Wobbles in the Barriers: Arctic Oscillation (4)

By: Dr. Ricky Rood , 4:22 PM GMT on October 14, 2013

Wobbles in the Barriers: Arctic Oscillation (4)

This is a continuation of my series on the Arctic Oscillation / North Atlantic Oscillation. Links to background material and previous entries are at the end.

In the last entry I suggested that if you were on a bridge overlooking a swiftly flowing creek then you would notice that twigs floating in the water did not move across the current. They are carried downstream along the edge of the current. The purpose of that comparison was to demonstrate how fast-moving, concentrated flows have the effect of isolating one side of the creek from the other. This is true in the creek, and it is also true about jet streams in the atmosphere.

One way to understand the Arctic Oscillation is to think of it as the variation of an atmospheric jet stream. For the Arctic Oscillation the jet stream of interest is the southern edge of vortex of air that circulates around the North Pole (see previous entry). Air inside the vortex often has characteristics different from air outside it. Intuitively for the Arctic, there is colder air on the side toward the pole. If you look at trace gases, like ozone, they are different across the edge of the vortex. The takeaway idea is that the edge of the vortex is a barrier. It’s not a perfect barrier, but the air on one side is largely separated from the air on the other side. In this blog, I describe the difference between a strong and a weak vortex – which is the same as the difference between the positive and negative phases of the Arctic Oscillation and the North Atlantic Oscillation.

Figure 1: This figure is from the point of view of someone looking down from above at the North Pole (NP). Compare this perspective to Figure 1 in previous blog. This represents a strong, circular vortex centered over the pole, which encloses cold air, represented as blue. The line surrounding the cold air is the jet stream or the edge of the vortex.

Figure 1 shows an idealized schematic of the North Pole as viewed from above. This is the strong vortex case, when there is exceptionally low pressure at the pole. Low pressure is associated with counterclockwise rotation in the Northern Hemisphere. This direction of rotation is called cyclonic. This strong vortex case is the positive phase of the Arctic Oscillation. During this phase, the vortex aligns strongly with the rotation of the Earth, and there are relatively few wobbles of the edge of the vortex – the jet stream. I drew on the figure two points, X and Y. In this case, the point X is hot and the point Y is cold. It is during this phase when it is relatively warm and moist over, for example, the eastern seaboard of the United States.

Figure 2 compares a strong vortex and a weak vortex. In both cases, the circulation around a central point is counterclockwise or cyclonic. However, in the weak vortex case, the vortex does not align as strongly with the rotation of the Earth and there are places where the edge of vortex extends southwards. The vortex appears displaced from the pole; it is not centered over the pole.

Figure 2: Examples of a strong, circular vortex and a weak, more wavy vortex. See text for a more complete description.

Whether the vortex is stronger or weaker is determined by the atmospheric pressure at the pole. In the winter, an important factor that determines the circulation is the cooling that occurs at polar latitudes during the polar night.

What determines the waviness or wobbles at the edge of this vortex? The structure at the edge of vortex is strongly influenced by several factors. These factors include the structure of the high-pressure centers that are over the oceans and continents to the south of jet stream. One could easily imagine a strong high-pressure center over, for example, Iceland, pushing northward at the edge of the vortex. This might push a lobe of air characteristic of the middle latitude Atlantic Ocean northward. Since the edge of the vortex is something of a barrier, this high-pressure system would distort the edge of the vortex and, perhaps, push the vortex off the pole. This would appear as a displacement of the vortex and its cold air over, for example, Russia. If the high grew and faded, then this would appear as wobbles of the vortex.

Other factors that influence the waviness at the edge of the vortex are the mountain ranges and the thermal contrast between the continents and the oceans. The impact of mountains is easy to understand. Returning to the creek comparison used above, the mountains are like a boulder in the stream. The water bulges around and over the boulder; the air in the atmosphere bulges around and over the mountain ranges. The Rocky Mountains in the western half of North America are perfect examples of where there are often wobbles in the atmospheric jet stream.

Figure 3: This figure is from the point of view of someone looking down from above at the North Pole (NP). This represents a weak, wavy, wobbly vortex displaced from the pole. The vortex encloses cold air, represented as blue. The line surrounding the cold air is the jet stream or the edge of the vortex. (definition of vortex)

Figure 3 shows an idealized schematic of the North Pole as viewed from above. This is the weak vortex case, when the low pressure at the pole is not as low as average and the pressure is much higher than the strong vortex case of Figure 1. This weak vortex case is the negative phase of the Arctic Oscillation. During this phase, the alignment of the vortex with the rotation of the Earth is less prominent, and there are wobbles of the edge of the vortex – the jet stream. In this case, the point X is cold and the point Y is hot. It is during this phase where it is relatively cool and dry (but potentially snowy) over, for example, the eastern part of the United States.

These figures help to explain the prominent signal of the Arctic Oscillation discussed in the earlier entries (specifically, this blog). That is, when the vortex is weak and wobbly, then there are excursions of colder air to the south and warmer air to the north. This appears as waviness and is an important pattern of variability - warm, cold, warm, cold.

The impact of the changes in the structure of edge of the vortex does not end with these persistent periods of regional warm and cold spells. The edge of the vortex or the jet stream is also important for steering storms. Minimally, therefore, these changes in the edge of the vortex are expected to change the characteristics of how storms move. Simply, if the edge of the vortex has large northward and southward extensions, then storms take a longer time to move, for example, across the United States from the Pacific to the Atlantic Oceans. In the positive phase of the Arctic Oscillation they just whip across. In the negative phase, the storms wander around a bit. A more complete discussion of this aspect of the role of the Arctic Oscillation will be in the next entry. (Note use of dramatic tension and the cliffhanger strategy of the serial.)

r

Previous entries:

Barriers in the Atmosphere
Behavior
Definitions and Some Background

August Arctic Oscillation presentation

CPC Climate Glossary “The Arctic Oscillation is a pattern in which atmospheric pressure at polar and middle latitudes fluctuates between negative and positive phases.”

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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##### 307. Patrap
 Never, bring a hacksaw to a logging match.
Member Since: December 31, 1969 Posts: Comments:
##### 306. MisterPerfect
 the statistics are from .gov sources
##### 305. Xandra
 Quoting 301. MisterPerfect:[...] By: Marc Morano - Climate Depot [...]Climate Denial Playbook: Marc Morano's History of Bullying Scientists(Click for larger image)
Member Since: December 31, 1969 Posts: Comments:
##### 304. overwash12
 I gotta admit,the church scene is a riot! Funny stuff!
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##### 303. BaltimoreBrian
 Mister aint perfect. ClimateDepot is a well known hack site that only denier sheep takes seriously.You have to be a complete crackpot to believe that Newton and Einstein are wrong about gravity.
##### 302. Naga5000
 @301Do you only read propaganda or do you ever delve into science? And what's up with your Al Gore obsession?
##### 300. JohnLonergan
 Contrary to claims by critics of wind power, Spanish researchers say, the turbines do reduce carbon dioxide emissions significantly even though the wind does not blow constantly. LONDON, 18 October – One of the most often repeated arguments of the anti-wind lobby is that the turbines produce electricity only intermittently, when there is enough wind to turn them. This, the critics argue, means that so much gas has to be burnt to provide a reliable supply of electricity that there is no overall benefit to the environment. But extensive research in Spain means this claim can now definitively be declared a myth. Wind, the researchers found, is a very efficient way of reducing carbon dioxide emissions. A study of 87 of the country’s coal and gas plants and how they were run alongside Spain’s very large wind industry found that adjustments made to the fossil fuel plants to compensate for variable wind strengths made little difference to their C02 emissions. The anti-wind campaigners claim that fossil fuel plants have to be kept running at a slow speed, all the time producing CO2, just in case the wind fails. At slow speeds these plants are less efficient and so produce so much CO2 – the opponents of wind say – that they wipe out any gains from having wind power. But a report published in the journal Energy by researchers at the Universidad Politécnica de Madrid says this is simply not true. There are some small losses, the researchers say, but even if wind produced as much as 50% of Spain’s electricity the CO2 savings would still be 80% of the emissions that would have been produced by the displaced thermal power stations. At lower penetrations, particularly when the number of wind turbines was small, each megawatt hour produced by wind replaced 100% of the CO2 that would have been produced by each displaced thermal megawatt.Read More ...
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##### 298. JohnLonergan
 Storm track shifts under climate change: what can be learned from large-scale dry dynamicsAbstractEarth’s storm tracks are instrumental for transporting heat, momentum, and moisture and thus strongly influence the surface climate. Climate models, supported by a growing body of observational data, have demonstrated that storm tracks shift poleward as the climate warms. But the dynamical mechanisms responsible for this shift remain unclear.To isolate what portion of the storm track shift may be accounted for by large-scale dry dynamics alone, disregarding the latent heat released in phase changes of water, this study investigates the storm track shift under various kinds of climate change in an idealized dry general circulation model (GCM) with an adjustable but constant convective stability. It is found that increasing the mean surface temperature or the convective stability leads to poleward shifts of storm tracks, even if the convective stability is increased only in a narrow band around the equator. Under warming and convective stability changes roughly corresponding to a doubling of CO2 concentrations from a present-day Earth-like climate, storm tracks shift about 0.8° poleward, somewhat less than but in qualitative agreement with studies using moist GCMs. Five eighths of the poleward shift is shown to be caused by tropical convective stability variations.This demonstrates that tropical processes alone (the increased dry static stability of a warmer moist adiabat) can account for part of the poleward shift of storm tracks under global warming. This poleward shift generally occurs in tandem with a poleward expansion of the Hadley circulation; however, the Hadley circulation expansion does not always parallel the storm track shift.* Corresponding author address: Cheikh Mbengue, Swiss Federal Institute of Technology Zurich–Geological Institute, Sonneggstrasse 5, 8092 Zurich, Switzerland. E-mail: cmbengue@caltech.edu
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##### 297. ScottLincoln
 Quoting 289. tramp96:Sometimes you can really be a not-so-friendly person. So eager to lash out at everyone else.
##### 296. FLwolverine
 #213 - Daisyworld, I've been meaning to thank you for that video. It's a good explanation. I'll bet Alley is a very interesting teacher.
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##### 295. goosegirl1
 **hint: mind your own business** Since I am a well known butt-in-ski, I was just wondering- why would you have a conversation on a public forum if you didn't want everyone to read it? Why not use wumail?Just to make this on topic ;))) I was just reading the following: Link
##### 294. ScottLincoln
 Quoting 282. DonnieBwkGA:Tramp96 your article says this"Not a single one of those winters with above normal snowfall in October featured above normal temperatures and below normal snowfall in the eastern half of the country,Not one. ZERO."But October 1989 had record snows in the Ohio valley. November and December were very cold and snowy but January and February 1990 were very mild and the winter turned out slightly warmer than normal in the eastern USA. The article is wrong.I think the methodology he is speaking of refers to snowcover in a particular part of Siberia.The thing that is lacking is the sample size of this correlation. A physical mechanism for the causation part would be nice, also.Quoting 287. DonnieBwkGA:But the article talks about the eastern USA and that's where the examples I give are coming from.It's about a teleconnection, which actually are known to occur. This one isnt well-established yet, however. So early season fall snowcover in Siberia correlates through a teleconnection to a cold AO, which favors higher snowfall and cooler temperatures in the eastern US.
##### 293. overwash12
 Quoting 281. tramp96:So it will be a warmer cold. Yes,It would. Does that make sense? It would be colder if we did not have AWG!
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##### 290. JohnLonergan
 Climate Context on Continuing Australia FiresTrue-color and false-color satellite views of a massive blaze in Australia’s Blue Mountains just west of Sydney alternate in this animation. (Images: NASA)More than two thousand firefighters continue to battle blazes across New South Wales in Australia, with more than 20 fires still uncontained despite easing weather conditions, the Australian Broadcasting Corporation reports.The animation above shows true- and false-color satellite images of one of those fires, in the Blue Mountains just west of Sydney on the coast. The false color frame, based on data from NASA’s Terra satellite, emphasizes the scar from the fire, which has so far torched a little more than 100 square miles — an area slightly larger than the city of Sacramento, California.The fires have erupted following some of the hottest climate conditions on record in Australia.The darker orange color in the map above shows the portion of Australia that experienced record high mean temperatures for the 12 month period between Oct. 1, 2012 and Sept. 30, 2013. That’s 39 percent of the country.In fact, the number of climatic records that have been broken over the past 12 months is truly astonishing. Here’s a summary from a report by the Australian Bureau of Meteorology:In the past 12-month period a large number of mean temperature records have fallen across Australia including:Australia’s warmest month on record (January)Australia’s warmest September on recordAustralia’s largest positive monthly anomaly on record (September)Australia’s warmest summer on record (December 2012 to February 2013)Australia’s warmest January to September period on recordAustralia’s warmest 12-month period on record (broken twice, for the periods ending August and September)Indeed, Australia’s warmest period on record for all periods 1 to 18 months long ending September 2013Two significant daily maximum temperature records were also set this year:Australia’s hottest summer day on record (7 January)Australia’s warmest winter day on record (31 August)Australia’s new Prime Minister, Tony Abbott, who took office in September, has dismissed evidence of climate change as “absolute crap.” He recently abolished the nation’s Climate Change Commission. But it has now been resurrected as an independent, privately funded organization called the Climate Council, which is dedicated to providing independent information to the Australian public.On its new web site, the Council has weighed in on the links between climate change and bushfires in Australia. Here’s an excerpt:Climate change can affect bushfire conditions by increasing the probability of extreme fire weather days. Many parts of Australia, including southern New South Wales, Victoria, Tasmania and parts of South Australia have seen an increase in extreme fire weather over the last 30 years. The projections for the future indicate a significant increase in dangerous fire weather for southeast Australia.
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##### 280. overwash12
 It still does not mean anything that we have a colder than normal winter this year. The trend is for the Earth to continue it's record warmth with all the co2,it has to.
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##### 274. JohnLonergan
 What Is Climate Change and What To Do About It? from Dr. John Baez at AzimuthSoon I’m going to a workshop on Interdisciplinary Perspectives on Climate Change at the Balsillie School of International Affairs, or BSIA, in Waterloo, Canada. It’s organized by Simon Dalby, who has a chair in the political economy of climate change at this school.The plan is to gather people from many different disciplines to provide views on two questions: what is climate change, and what to do about it?We’re giving really short talks, leaving time for discussion. But before I get there I need to write a 2000-word paper on my view of climate change—’as a mathematician’, supposedly. That’s where I want your help. I think I know roughly what I want to say, and I’ll post some drafts here as soon as I write them. But I’d like get your ideas, too. ... Read more ...Here are the drafts of two talks Dr. Baez will be giving:WHAT IS CLIMATE CHANGE?WHAT TO DO ABOUT CLIMATE CHANGE?The discussion thread, where Dr. Baez and the commenters discuss and critique the drafts, is worth a read.
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##### 273. ChillinInTheKeys
 Or if you have a short attention span, You can watch these in a minute or two..."Coastal flooding getting worse with sea-level rise".LinkLinkMy shop in Sugarloaf Key had water 3" from coming in my door this morning!
##### 272. Some1Has2BtheRookie
 Friday is the day of the week that new movies are usually released to viewing in the theaters. I have already seen "Gravity" and not much else interests me at the theaters for today. So, may I offer some older movies worth viewing?1. Climate Change -- the scientific debate2. Climate Change -- the objections3. Climate Change -- Anatomy of a myth4. Climate Change -- Gore vs. Durkin5. Climate Change -- isn't it natural?6. Climate Change -- Those hacked e-mails7. Climate Change - "Those" e-mails and science censorship8. Climate Change -- Has the Earth been cooling?9. Climate Change - Meet the Scientists10. Climate Change - An imminent ice age debunked11. Climate Change -- Hurricanes, atolls and coralAnswering Climate Change Skeptics, Naomi OreskesFresh Popcorn is available in the lobby! - tipping is allowed!Enjoy your weekend, everyone!
##### 271. Neapolitan
 Quoting 262. Patrap:When was the last time the Atmosphere had 400ppm of CO2?Back when Northern Canada was as warm as Panama. Yeah, right about then...
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##### 270. georgevandenberghe
 Well I learned something basic (no pun intended) from post 266. I didn't know ocean PH was over 8.
##### 269. georgevandenberghe
 Quoting 261. Some1Has2BtheRookie:You and Anthony Watts need to discover the difference between a scientific hypothesis and a scientific theory. The AGWT is a scientific theory. Thus the AGWT and not the AGWH. ... Oh, wait! That was just an attempt by you to distort and to confuse. ... Sorry. Carry on!And I was going to say that the "hypothesis is dead" It's morphed to a much more solid and well supported by evidence THEORY and on its way to be verified by events as validated FACT.
##### 266. JohnLonergan
 EPA Sued to Stop PacNW Ocean AcidificationThe Center for Biological Diversity is suing the EPA -- again -- for failing to halt ocean acidification in the Pacific Northwest.CBD is a private, membership environmental organization (625,000 members) based in Tucson. They sued the EPA for the same thing back in 2009, and the EPA agreed with them and said it could address ocean acidification under the Clean Water Act.But the EPA hasn't done much since, so CBD is going in again.Read more at Quark Soup >>>
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##### 265. Patrap
Member Since: December 31, 1969 Posts: Comments:
##### 264. ScottLincoln
 I seem to recall at some point in the last few days someone dropping a quick link and note into the thread claiming that the "hockey-stick" keeps getting less and less notice by the IPCC. The suggestion was that it was becoming less and less correct, and the IPCC was adding back in the Medieval Warm Period. Didn't have a chance to address it at the time.Looks like the same conclusion in the AR5 Technical Summary as we had from the infamous reconstruction of Mann.
##### 262. Patrap
 When was the last time the Atmosphere had 400ppm of CO2?
Member Since: December 31, 1969 Posts: Comments:
##### 261. Some1Has2BtheRookie
 Quoting 241. Cochise111:More evidence that the AGW hypothesis is dead:LinkYou and Anthony Watts need to discover the difference between a scientific hypothesis and a scientific theory. The AGWT is a scientific theory. Thus the AGWT and not the AGWH. ... Oh, wait! That was just an attempt by you to distort and to confuse. ... Sorry. Carry on!