Atmospheric teleconnections what the heck is that all about? Well, let's learn a little bit about these things. What are the key point? What is an atmospheric teleconnection? What it is, is a connection between climate and weather conditions between widely separated locations on our planet. Now this several important ones that affect the Arctic, the North Atlantic Oscillation, the NAO, sounds like a good name for a rock band. Something called the Arctic Dipole Anomaly and then also something called the Pacific Decadal Oscillation. So let's learn a little bit about these. First, the North Atlantic Oscillation. What is this? It's a correlation or covariance we would say, a relationship between the strength of the Icelandic low and the Azores High. Basically what this teleconnection is telling us is that when the Icelandic Globe is strong, that means the pressure is low. The Azores, High high pressure area is strong and vice versa on the Icelandic low is weak, the Azores High is also weak. Turns out that why is this important is that it has really big effects on patterns of Arctic temperature and precipitation. Now let's learn a little bit more about this. Take a look at the right hand side of this figure, which is showing when the NAO is in what we call a positive-mode. Now what you'll see there is these two circles that are marked H and L. Now age is high pressure, we learn that earlier, L is low pressure. What we have that H down there, okay? That is the Azores High and so basically an area of pretty semi permanent high pressure and remember that the circulation around a high pressure cell is basically clockwise. Now to the North you see that L, that is marking the location of the Icelandic low. This is an area where there's just generally lots and lots of cyclones. Cyclones moving into their from the south, cyclone forming there right within that region as well. Now the issue is that H and L, okay? The strength of those H and Ls you could even think of it as the size of the circles, okay? Is big when the NAO in the positive-mode. What this is saying is that when the North Atlantic oscillation is an appositive mode, that Icelandic low is strong, the pressure is low. Now, also, when the NAO is in a positive-mode that Azores High to the South, that's also strong, really high pressure. Now the flow around the low pressure is counterclockwise, the flow around the high pressure is clockwise. So between those two it's kind of an eggbeater effect because the winds are going to be blowing pretty strongly from West to East, which is affecting storm tracks. And what happening here is when there's North Atlantic Oscillation is positive, it's pumping all kinds of warm moist air well into the Arctic. The contrast is when the North Atlantic Oscillation is in its negative mode that shown on the left. See how the circle for L and H are smaller? What this is really just trying to illustrate is that the Icelandic low is weaker and the Azores high is also weaker, that eggbeater effect. In other words, the clockwise flow around the high pressure the counter clockwise flow around the low pressure is not so pronounced. So you're not really pumping all this warm air up into the Arctic anymore, and storm tracks are also shifted. So this is what we're talking about when we're talking about the North Atlantic Oscillation an oscillation between the positive-mode on the right. And then negative-mode on the left. Now we can describe this simply in terms of an index, by really just looking at the pressures in the middle of that Icelandic low and in the middle of that Azores high. We can determine an index, and if it's positive it means the NAO is in a positive-mode. If the index is negative, it means it's in a negative-mode. Remember, positive-mode, strong Icelandic lows, strong Azores high negative-mode, just the opposite. Now we have a record of this going way back into the 1800s and what you can see is it bounces around from positive, negative, positive, negative. Now this we're looking at winter December through March and these are the seasons. These are the months the season, winter basically, when the North Atlantic Oscillation tends to be best expressed, And what you can see is it really bounces around. One winter it's positive, the next winter, it's negative, and so on. You can have runs of years where it tends to be positive, runs of years where it tends to be negative. And we can relate this to big scale changes in patterns of temperature and it churns out precipitation across the Arctic. Here's an example. Now on the left, I am showing the sea level pressure anomalies when the North Atlantic Oscillation is in a positive mode. What I mean by this, this is the pressure compared to average. So I'm taking the average pressure everywhere, and then I'm just looking at the case when the North Atlantic Oscillation is positive. And I'm making a map of just the difference between the NAO positive and average. And what you can see, here Greenland is in the upper left quadrant, is when the NAO is positive. What we have is very much a below average pressure over the North Atlantic sector that's shown in those blues and purples. That makes sense because the Icelandic Low is strong. Now compare that one to the right. That's when the North Atlantic Oscillation is negative, weak Icelandic Low. And so you can see the pressures over that North Atlantic sector in particular are well above normal. But they're really well above normal across really most of the Arctic. Now here's the associated pattern of temperature anomaly, that's departures from average. On the left, when the North Atlantic Oscillation is in that positive mode, and what you can see is temperatures are well above average. They're in those yellows and the oranges across basically most of Northern Eurasia. So it's a really big signal when that North Atlantic Oscillation is positive. But on the other side of the Arctic, we see that temperatures are below average that's shown in those purples, that's around Greenland, Baffin Bay. Now the picture on the right is showing just the opposite. That's when the North Atlantic Atlantic Oscillation is negative. You can see basically it's the reverse pattern. Temperatures over Eurasia, well below average, while those over Greenland, Baffin Bay, that sort of region, are well above average. So you see this flip flop going on as the NAO goes from positive to negative, from negative to positive. And we see that it's associated with these big scale patterns of temperature anomalies. Now here's a question. How long have the effects of the North Atlantic Oscillation on weather conditions been recognized? The answer is that it all goes all the way back to the days of the Vikings. They didn't have something called the North Atlantic Oscillation. They didn't have ways to measure it like we do today. But they certainly knew the effects of the North Atlantic Oscillation from their travels from Northern Europe across to Greenland. So what really goes back quite a long time, at least a recognition of the effects of the North Atlantic Oscillation. Now here's another of these teleconnections called the Arctic dipole anomaly. What this is talking about is a pattern of high pressure over the Arctic Ocean, North of Alaska and low pressure over eastern Siberia. This one's basically a summer pattern. That's when you see it's best expressed in summer, big effects on temperature over the Arctic associated with low September sea ice extent. In summers when that Arctic dipole anomaly is present or positive, we tend to have low September sea ice extents. You can again see these big effects on Arctic weather climate patterns sea ice. Now here's what it looks like. What I'm showing here is the sea level pressure pattern on the left for the summer of 2007. And the summer of 2007 is really the exemplar of the Arctic dipole anomaly. What we have over the Arctic Ocean, North of Alaska, high pressure that's shown in the yellows and the oranges. And to the left, you see in this figure over Eurasia, in those purples and blues, low pressure. Now remember, over high pressure, winds tend to be clockwise. Low pressure, wind tends to be counterclockwise. So between those high pressure and low pressure patterns, the winds are basically coming from the south and winds from the south are warm. So it's pumping all kinds of heat up into the Arctic because of the high pressure and low pressure patterns, and that's what you see on the right. This is looking at the departure from average of temperatures over the Arctic during the summer of 2007. And you can see between that high pressure and the low pressure pattern, you see how warm it was. And that's shown in the yellows and the oranges and the red, well, well above average. Makes sense, this ate up a lot of sea ice. Summer of 2007, well, in 2007 in September, turns out at the time. And that was the record low sea ice extent for September. It's sense been surpassed by the year 2012, but it was pretty remarkable at the time. And what was happening is with that dipole anomaly pattern, it was pumping all kinds of warm air into the Arctic Ocean, especially over the East Siberian Sea. And it was just melting a heck of a lot of sea ice. Also the winds associated with that, it was blowing the sea ice away from the shore and shoving it into the northern parts of the Arctic Ocean, resulted in very very low sea ice extent. So when we think about years and we're ask ourselves, might there be very low sea ice extent this September, one of the things we look for is what the Arctic dipole anomaly is doing. Here is just one more, the Pacific Decadal oscillation. Now this has an index based on North Pacific sea surface temperature anomalies. Again, these are departures from average. And the Pacific decadal oscillation tends to vary more decade to decade. It's kind of a longer lived pattern than the North Atlantic oscillation which shifts around pretty quickly, and the Arctic dipole anomaly, which can do the same sort of thing. Tends to vary more by decade. Positive mode, what we find is warm over Alaska, also warm over the Arctic Ocean. When the Pacific decadal oscillation, or the PDO as it sometimes known as, is in a negative mode, tends to be cold over Alaska and also cold over the Arctic Ocean. This is just showing the pattern of sea surface temperature anomalies when the Pacific decadal oscillation is in a positive mode. You see that on the northern North Pacific around Alaska, very very warm. Kind of a cold pool south of there, and then very warm in the tropical Pacific Ocean. This has some relation, as it turns out, to something that some of you may also heard of, which is the El Nino pattern as well. But the Pacific decadal oscillation is something that tends to vary over a longer time scale. And so what we see here, here's an index of the Pacific decadal oscillation going all the way back to like 1900. This goes back quite a ways and you can see yes, certainly it varies from year to year. And but what you see is it tends to get stuck preferentially in one mode for awhile, then it tends to get stuck in another mode for awhile. So it tends to stick around in one mode, typically longer than we would see for something like the North Atlantic oscillation. Now here's a question. Are the phases an intensity of different teleconnections likely to change as the climate warms? And the answer is certainly at least to my mind is maybe. It's really kind of an open question. There's some evidence that this would happen. There's some evidence that, well, maybe a bit, but maybe they're going to change a bit, but not a whole lot. We'll see, this is actually an open question in climate science about how the phases and intensities of these different teleconnection patterns might change through time. Now, just for briefly, here's the temperature anomalies for the Pacific decadal oscillation in the positive mode on the left, and the negative phase on the right. So when that PDO is in a positive phase, you see how warm it is over Alaska. And you see it's fairly warm, that's in those yellows, over a lot of the Arctic Ocean, but see it's below average temperatures over a lot of Northern Eurasia. On the right it's showing the temperature anomaly pattern associated with the negative phase of the Pacific decadal oscillation. And you can see now it's cold over Alaska, cold over a lot of Canada. So the lesson here is that these teleconnection patterns have big effects on patterns of Arctic temperature and precipitation. We really talked here just about the temperature effect, but yes, precipitation patterns are also involved. So thank you very much.
