# Barriers in the Atmosphere: Arctic Oscillation (3)

By: Dr. Ricky Rood , 12:50 AM GMT on October 03, 2013

Barriers in the Atmosphere: Arctic Oscillation (3)

I want to continue with the Arctic Oscillation / North Atlantic Oscillation. First, however, here is the link to my August presentation. Also here is a link to the GLISAclimate.org project workspace where I collected together the materials I used in the presentation - Arctic Oscillation: Climate variability in the Great Lakes.

Here are the previous entries in the series:
Behavior
Definitions and Some Background

This blog is mostly a setup for the next one. (And yes I did notice that the IPCC AR-5 report was released, but I don’t have anything different to say about it than many of my more able colleagues. I’ll get to it.)

In the talk that I linked to above, I used a couple of diagrams that the audience told me worked very well. I am going to try them out in this blog. In the previous blogs I used the CPC Climate Glossary to give the definition of the Arctic Oscillation. “The Arctic Oscillation is a pattern in which atmospheric pressure at polar and middle latitudes fluctuates between negative and positive phases.” This definition does not really do much for me. It’s one of those definitions that I imagine if I ask 10 atmospheric scientists to tell me what it means, I will get 12 answers. Therefore, I will draw a picture.

Figure 1: Adapted from Jim Hurrell – This picture is a schematic representation of the positive and negative phases of the Arctic Oscillation. In the positive phase the pressure is low at the pole and high at middle latitudes. This is the positive phase because if you calculate the difference between middle and high latitudes it is large. In the negative phase the pressure is not as low at the pole and not as high at middle latitudes. This is the negative phase because if you calculate the difference between middle and high latitudes it is small. The refrigerator suggests that this is like opening and closing the refrigerator door (see Behavior).

This figure helps me with the definition. I want to focus on the low pressure at high latitudes, which in this figure is drawn idealistically at the pole. In reality, it is likely to wander off the pole, a fact that will be important in the next blog. When the pressure is low at the pole, then there is a stronger vortex of air circulating around the pole. When the pressure at the pole is not as low, then there is a weaker vortex. In both cases, strong or weak vortex, the air generally moves from west to east.

For clarity, vorticity is a parameter that describes rotation in a fluid. A vortex is a feature in a fluid dominated by vorticity – that is it is rotationally dominated. Tornadoes and hurricanes are weather features that we often call vortices; there is an obvious circulation of air in these features. In the Earth’s atmosphere at middle and high latitudes rotation is an important characteristic of the flow, due to the rotation of the Earth. The reason air moves in the west to east direction for both the weak and strong vortex cases of Figure 1 is that the rotation of the Earth is important to the flow.

In Figure 2 I have set up an even more idealized figure. I also provide this link to a Powerpoint animation, that I am not smart enough to incorporate into the blog. In the animation I have five slides that clarify the point that I make in Figure 2.

Figure 2: A vortex and a ball. In the center of the figure is low pressure, meant to be an analogue to the vortex over the pole in Figure 1. Parcels of air move around the low pressure system. If it takes the same amount of time for a parcel farther away from the low pressure center to go around the vortex as a parcel nearer the center, then the parcel farther away has to go faster because the distance it has to go is longer. That is why I drew that arrow, saying that air moves “faster” at the outside edge of the vortex.

To set my point a little more, imagine you are on a bridge overlooking a running stream. If you drop a stick in the water near the edge where the water is moving slowly, then if the stick drifts towards the more rapidly flowing water, it is carried downstream at the edge of the fast moving water. It does not cross the core of fast moving water – this jet of water. In fact the jet is something of a barrier that keeps material from crossing the stream. Material is transported downstream.

Back to Figure 2: Imagine that you want to roll a ball into the center of a vortex. As the ball gets to the edge it gets caught up in the flow and pulled around the edge. It does not roll into the center. Look at the this link to a Powerpoint animation to get a better idea of what’s going on.

Now go back to Figure 1. The vortex in Figure 1 is also a barrier. The southern edge of vortex is a jet stream. Air on the two sides of the vortex often has different characteristics. Intuitively, there is colder air on the poleward side. 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 air on one side is largely separated from the air on the other side. In the next blog, I will describe the difference between the strong and the weak case and its relevance to weather, climate and, perhaps, climate change.

r

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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##### 20. Some1Has2BtheRookie
 Your blog topic is an interesting read, Ricky. I look forward to your expansion on this in the next blog.
##### 18. RickyRood
 And even worse it's in the NPS talk and the animation ... got to get my editor (sister) back in the mix.before long I'll be saying there's no their there or want no what to where when I'm there I'm not even very good at being clever ... Quoting 10. Patrap:Me tinks maybe datz a "spelling" error on the Image.It's "Ball"We dont get to say dat un here everyday.; )
##### 14. barbamz
 Thank you for the comprehensive explanations and graphics, Dr. Rood; very appreciated. And those penguins in the powerpoint file really made my smile :)Link
Member Since: December 31, 1969 Posts: Comments:
##### 13. RickyRood
 That's worse that a spelling error ... It's old man trying to do too many things cognitive slippage. That's how you end up at Dallas instead of Dulles ...Will change (after class).rQuoting 10. Patrap:Me tinks maybe datz a "spelling" error on the Image.It's "Ball"We dont get to say dat un here everyday.; )
##### 12. JohnLonergan
Member Since: December 31, 1969 Posts: Comments:
 Re: Comment 8Right wing Republican think tank staffers working on ways to spin the death of the oceans:Jellyfish - its the new omega-3 source; *** Now with no Omega-3's ***Jellyfish - Yummy in the tummy (just watch those poisonous spines)Jellyfish - You'll wish you never ate tuna.
##### 10. Patrap
 Me tinks maybe datz a "spelling" error on the Image.It's "Ball"We dont get to say dat un here everyday.; )
##### 9. SteveDa1
 Quoting 6. cyclonebuster:Try to roll the box towards the vortex? How do you roll a box?I don't get it either.It must be a typo; I think they meant ball.
##### 8. JohnLonergan
Member Since: December 31, 1969 Posts: Comments:
##### 7. Xandra
 Glaciologist Aslak Grinsted says the IPCC are too optimistic and over-confident in their ice-sheet predictions and that the ice sheet experts are actually more pessimistic.Optimistic & over-confident ice sheet projections in AR5 "AR5 process based model projections are much more conservative/optimistic and has much more narrow uncertainties than the ice sheet experts (Fig.1). There can be no good reason for why the AR5 authors have much greater confidence in their ability to project ice sheet loss than ice sheet experts themselves. Notably the best guess view of ice sheet experts nearly falls outside the AR5 process based range. The worst case scenario from ice sheet experts is more than 60 cm higher than the worst case from the AR5 process models."Figure 1: Projections of ice sheet mass loss over the 21st century under RCP4.5. The AR5 process based projections appear optimistic and over confident when compared with views of ice sheet experts.More from Aslak Grinsted:AR5 sea level rise uncertainty communication failure "I am disappointed in how the sea level rise projection uncertainties are presented in the IPCC AR5. The way the numbers are presented makes people believe 98 cm by 2100 is a worst-case scenario which it clearly isn't. The AR5 does have caveats which explains why it could be more, but unfortunately this is buried in language that clearly goes over the heads of most people."
##### 5. BaltimoreBrian
 Quoting 2. Astrometeor:Thanks for the set-up Dr. Rood, looking forward to the next blog sir!I feel as if Brian was tuned in with your new posting Doc, he plussed it before my computer could even load the blog...lol.Face it astro. I'm just older and faster ;)
##### 4. BaltimoreBrian
 This article just came up and it is important enough that I am adding it now.!!! How to detect pseudo-science B.S.
##### 3. RevElvis
 The Story of Solutions The Story of Solutions explores how we can move our economy in a more sustainable and just direction, starting with orienting ourselves toward a new goal.In the current 'Game of More', we're told to cheer a growing economy – more roads, more malls, more Stuff! – even though our health indicators are worsening, income inequality is growing and polar icecaps are melting. But what if we changed the point of the game? What if the goal of our economy wasn't more, but better – better health, better jobs and a better chance to survive on the planet?Truth-Out.org
##### 2. Astrometeor
 Thanks for the set-up Dr. Rood, looking forward to the next blog sir!I feel as if Brian was tuned in with your new posting Doc, he plussed it before my computer could even load the blog...lol.

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