In previous videos, I introduced this concept of Arctic amplification. This is the observation that temperatures at and near the surface of the Arctic are rising considerably faster than the rest of the planet. It's really an Arctic amplification of air temperature change, something that emerged maybe about three decades ago. Now, the thing about the climate system is pretty much everything is connected to everything. An interesting issue that has arisen is a possible connection between the Arctic amplification, that strong warming in the Arctic compared to elsewhere, and whether patterns in middle latitudes. Notably, we're talking about the cyclones, the cyclones that have their warm fronts and their cold fronts, and the shape of what we call the jet stream pattern. The idea here, is that the Arctic amplification may influence mid-latitude weather patterns by changing the jet stream. Now the jet stream is this band of high strong winds, fairly high in the atmosphere. What happens is that, storms will tend to develop along particular regions of that jet stream within kinks in that jet stream, what we call trough. Now the thing is, the argument anyhow, is with the Arctic amplification, we can make that jet stream wavier, so stronger kinks. The idea here is that, well, we changed the tracks of storms, we could change the intensity of storms. We could also get what we call stuck patterns where one part of say, North America or the United States gets stuck in a deep freeze with storms and things like that. Well over in Alaska, for example, it's too warm to start the I did a rod where they need to start it, because of this very wavy jet stream pattern. Now the issue, however, is still very controversial. There's some scientists out there saying, "Oh yes, this is already happening, and I know why I can tell you why." There are other scientists out there saying, "Not so fast. I don't really see it." It is a very controversial thing and there's a lot of research being done on it. Hopefully we'll have some answers soon. Now how it works, so if we look at the atmosphere, there's a temperature gradient from the South to the North. In other words, the atmosphere is warmer to the South than it is in the North. That's why it's nice and warm in Hawaii and cold in the Arctic. That of course, has to do with differential solar heating. The sunshine is more strongly in lower latitudes than in the higher latitudes. Now, the thing is, the temperature gradient gives rise to the jet stream, and the jet stream develops with a temperature gradient. That gradient between the South and the North, is particularly sharp. All right, so if we warm up the Arctic is the idea, we can influence that temperature gradient that influences the jet stream. The argument is it makes it more wavy, causes changes in storm patterns, and we can get the stalling patterns, we can get stuck in one mode or another. Where you get a deep freeze here, and it's very warm over here, that's the basic idea. Now this picture here is showing Arctic amplification. This is an illustration of temperature changes from 1961 through 2018. I could have added 2019 in here, but it's not going to change things. You can see where the warming has been is in the warm colors, the yellows and the oranges, and the reds. But look at where it's really gotten more the Arctic. That's your Arctic amplification that we're talking about. Now, here's a question, were scientists surprised to see the emergence of Arctic amplification? The answer is no. Really it was expected for a long time. In fact, it was predicted back in late 19th century that we would eventually see it and we have, it emerged over about the past three decades or so. It's a case where our theory has come very much into line with what the observations are actually showing. All right, let's talk a bit about this temperature gradient and the jet stream. This image here is trying to illustrate some of these linkages. You look on the x-axis here, its latitude going from zero latitude, that's the Equator all the way to the right, which is 90 degrees North, that's the North Pole. On the y-axis is altitude in kilometers. Now, the thing is, in the South, the air is warmer and basically less dense than the air to the North, which is colder and it is more dense. There is a temperature gradient between the lower and the higher latitudes. In other words, if I were to say eight kilometers up in the atmosphere, a lower latitudes, the temperature there would be considerably higher than an eight kilometers up in the atmosphere at a higher latitude there's a temperature gradient. That temperature gradient is particularly sharp in the middle latitude, that's where the jet stream lies. I'm trying to show, where that jet stream is. It's fairly high in the atmosphere. But that's key, because it really controls where the storms form and where they track. That's the key. But you can see just from this, what would happen if we warmed up the Arctic strongly, that dense air up there would heat up, expand, and become less dense, and the idea is that it would alter the temperature gradient, alter the jet stream, and alter the storms. That's the link. Now, I'm looking at it here in a little different way. What I'm looking now, there's two maps. The one front on the left is looking top down from the pole. It's looking at temperatures in January, middle of January, at 500 millibars That's basically a pressure level halfway up in the atmosphere, and it's showing the temperatures. Now, the temperatures increase as we go south or decrease as we go north. The cold air is in those purples and those blues. The warm air is in those warmer colors. That's the temperatures. Now, it turns out that that is going to set up a strong pressure gradient as well, and it's a pressure gradient that will initiate the wind. What we find is that the jet stream will tend to be found along that area where there's particularly strong temperature gradient, because that's where there's also a particularly strong pressure gradient. I'm trying to illustrate it in this figure here, where I'm showing in the red, a long-term average where that jet stream lies, and I'm trying to show it in that red line. That's where the temperature gradient and that pressure gradient are strongest. Now, this north of the jet stream, that's the cold air, that's the cold arctic air. South of the jet stream, that's the warmer air of the subtropics and the tropics. The boundary between them is where the jet stream lies. Now, the jet stream and the colder air to the north, the colder to the north of the jet stream, that's what we call the polar vortex. Now, you've probably heard on the news sometime about things like invasion of the polar vortex. Well, all the polar vortex is, is this area of cold air, north of jets stream, and the jet stream divides that cold polar air from the warmer air to the south. Now, that jet stream can change. It can change. It can become more sinuous or less sinuous. Here's just an example. I forget what month I'm showing here, but it's showing a situation with a more sinuous pattern. I'm, again, showing where the jet stream is lying from that red line. Now, the thing is the jet stream tends to determine where the storms form and how they track. They tend to track and move along the jet stream, and they form in certain places in the jet stream, notably ahead of the kinks. Those blue circles that I'm showing are showing the areas ahead of the kinks where we're likely to see storms and storm formation. That's relationship that we have, the storms tend to form north or just east of the kinks. Now, that particular chart, I said I didn't know when it was from. Here, I show it right there, it's for November of 2018. The idea, however, of the Arctic amplification is it changes the temperature gradient. What it does, the argument is it makes the jet-stream more wavy so there's stronger kinks where the jet stream dips to the south and the storms form ahead of the kinks. Also, it makes what we call stronger ridges where the jet stream moves far to the north. That's where it's warm, because you're in the warmer air. So the idea with Arctic amplification, in some areas, you have invasions of the polar vortex, which is just meaning that one of these kinks is now moving down south into your area. Whereas in other areas, you get strong ridges, and that's where we have the warm air, but that's the argument behind this whole Arctic amplification. The one on the left is calling what we'd call a stable polar vortex, where there's really not a lot of strong kinks. The one on the right is the wavy polar vortex, where there are a lot of kinks. The argument is the Arctic amplification can give you a pattern like the one that looks on the right. Now, here's a question. Was the term polar vortex invented by the media? Answer is no. No, meteorologists have been using the term polar vortex for a very long time. The media glommed onto this with these talks about the invasion of the latest polar vortex and things like that, and meteorologists tend to laugh at this because we say, "Well, all that's meaning is that there's an invasion of cold air coming down. You're getting into one of those kinks in the jet stream." Any case, it's an interesting story about how the media can take on these things. I hope you've learned a little bit about this link, potential link between the Arctic amplification and what can be happening down in middle latitudes. Now, I have to emphasize that this is still controversial, with a lot of scientists saying, "Yeah, absolutely, this thing is happening." Other scientists are saying, "Not so sure." Hopefully, soon we'll have more answers to this, because it is indeed a fascinating topic. Thank you.
