Ep. 516: Polar Vortices

Posted on Jan 31, 2019 in Planetary Science, podcast | 0 comments


It’s cold right now. Okay, fine, here on Vancouver Island, it’s actually pretty warm. But for the rest of Canada and big parts of the US, it’s terrifyingly cold. Colder than Mars or the North Pole cold. This is all thanks to the break up of the polar vortex. What are polar vertices, how do they form, and where else to we find them in the Solar System?

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Show Notes

Polar vortex
What Is a Polar Vortex?
What is the Polar Vortex?
Subtropical Jet Stream
Venus polar vortices
Venus Express Vortex reports
Polar vortices across the solar system
Saturn’s hexagonal polar vortex
Jupiter’s octagonal polar vortex
Physics of standing waves
Titan’s polar vortex

Transcript

Fraser Cain: Astronomy Cast, Episode 516: Polar Vortices’. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos. Where we help you understand not only what we know, but how we know what we know.

I’m Fraser Cain, publisher of “Universe Today,” with me as always, Dr. Pamela Gay, a senior scientist for the Planetary Science Institute, and the director of Cosmo Quest. Hey Pamela, How ya doin’?

Dr. Pamela Gay: I’m doing well, how are you doing?

Fraser: Good, where are you, right now?

Dr. Gay: I am in the visitor’s office at the Planetary Science Institute’s headquarters, in Tucson, Arizona. It is a very boring room, in a very exciting building.

Fraser: Right, so you are a senior scientist for the Planetary Science Institute, and now, a senior scientist at the Planetary Science Institute.

Dr. Gay: Exactly.

Fraser: Right, that’s the thing that people don’t realize, of course, is that in this new virtual world, Pamela’s always on the move. Normally, working from home, but every now and then you get a chance to actually go into the office, and hang out and visit with people there. Actually, I’ll get into weather in a second. But, what’s it like? How big is the place?

Dr. Gay: So, I haven’t actually figured out how many people are located here. It’s in the tens, I can tell you that much. Planetary Science Institute in general, has over 100 PhD’s and all their support staff. This means that like Susie’s gonna be working at the Planetary Science Institute.

Nancy gonna to be working at the Planetary Science Institute, and part of the reason that I’m here is to work on transforming all of your donations, all you wonderful people out there in the audience into offers of employment, to all of our staff. So, your Patreon contributions are the reason Susie has a job and can pay tuition for her daughter in college. So, if you’ve thought about supporting us on Patreon, and have never really done it; you need to go to Patreon now, and help Susie get paid.

Fraser: Perfect. All right, so it’s cold, right now. Okay fine, here on Vancouver Island is actually pretty warm, but for the rest of Canada and big parts of US it’s terrifyingly cold. Colder than Mars or the North Pole cold; this is all thanks to the breakup of the polar vortex. Where polar vortices? How do they form, and where else do we find them in the solar system? So ironically, of course, where you were, just days ago, was at the heart of the polar vortex. How bad is it, back at home? Your husband, when you talk to him what kind of frozen state is he experiencing?

Dr. Gay: I really have survivor guilt this week. It has been getting to a wind chill of -25 Fahrenheit, which is minus tens of degrees centigrade. It is so cold our dogs are not allowed outside for more than five minutes. Because, their eyeballs and noses, and things like that will start to freeze, in bad ways. We’re in St. Louis where normally this time of year is right around freezing, plus or minus a few degrees. To go from right around freezing to an air temperature of – before the wind chill happens – about 0° to plus or minus 5°F, to -15° plus or minus a few. It sucks.

Fraser: Yeah, here normally we hover like in the three, four degrees centigrade. What’s that? Sort of in the in the mid-thirties–

Dr. Gay: Yeah.

Fraser: – for the Fahrenheit folks. We can have cold snaps that’ll takes down to about -10 like a really bad winter cold snap is -10 Celsius, which is in the low teens, I guess, for you, or the lots. But, yeah this polar vortex is hitting the folks in the US. I’ve heard wind chills in Chicago of minus–

Dr. Gay: Minus 40. Yeah, okay.

Fraser: – Fifty-five. I’ve heard -55. And, Winnipeg, which is just a really, really cold place, is experiencing just insanely cold weather and they are blaming this on the polar vortex, or more specifically the polar vortex not doing what it’s supposed to be doing. It’s moved, so what is a polar vortex?

Dr. Gay: Worlds like our own Earth, that have variations in temperature between the equator and the pole will end up with these convective cells. This is super easy to see in images of Jupiter. Where you see these bandings of lighter and darker material that are actually counter-rotating around the world. Well, here on earth we have a series of jet streams.

We have the tropical jet streams and the polar jet streams, and these are demarking the areas where we have our own alternating bands. Our own convective cells within the atmosphere. Ideally, you have this great – the pole is super cold, and you have this nice low density super cold mass of air that is counter-rotating at the top of the world; at the bottom of the world. There are jet streams on both sides that are locking those in.

Then, you have another band of warmer air, another band of even warmer air and you have these alternating bands with these jet streams, and everything stays put, because of thermodynamic differences. The colder the Arctic, the warmer the equator; the happier the planet.

Fraser: And, that’s what happens normally. We should definitely, sort of, go down the rabbit hole for a moment just to talk about how it’s all gone horribly, horribly wrong, right now. But, then go back into more normality, and sort of deal what it’s supposed to be. How is everything gone horribly, horribly wrong, right now?

Dr. Gay: Well, the reason that you are in a good place, in St. Louis, where you and I normally have about the same whether–

Fraser: Yeah.

Dr. Gay: – is those Rocky Mountains serve as a buffer, for you. You’re on the correct side, and death for me. Because, the jet stream is sort of like, I don’t know where to be. The temperature gradient isn’t what it should be. And, that blob of cold air sitting on top of the world, instead of being a tightly focused cyclone of air, has fragmented into multiple low density, low-pressure pockets; and those pockets are wondering free, and they’re coming my way instead of your way. ‘Cause they’re just drooping down those Rocky Mountains.

The air coming off the Rockies is shaping where they end up going. This isn’t just a North American thing. We also find that the Ural Mountains in Russia cause a similar effect to occur. Where Siberia periodically, also gets a polar vortex sitting on top of it, and it’s just the jet stream no longer being correctly shaped. Because, there aren’t the thermal gradients to drive where it hangs out, as there should be.

Fraser: So, you get this situation – I mean, I sort of think, and I don’t know if this is the exact same situation, but you opened the door to one of those big walk-in freezers, right and warm air from where you are goes into the freezer and the cold air spills out. And, normally the – all of those temperature gradients, all of those spinning bands that are going across the planet, that are routing around the landforms on the earth, are acting like this natural barrier.

They are the walls of the freezer that are keeping that incredibly cold air properly up in the poles, and down in the poles where it belongs. But, in this situation you can see the simulations. NASA does these amazing simulations of where the wind patterns are going where the warm air is and where the cold air is, and these beautiful, almost artwork like maps showing these arrows of where things are, and temperatures and so on.

And, you can see these jet streams which normally stay – they push up along, as you said, up along the mountains and they curl away off into the ocean on both sides. That’s one of the reasons why Iceland is so reasonably warm is you get this jet stream that passes right above Iceland when it normally should be -40 it’s freezing or just a little below.

Dr. Gay: Our oceans also hold onto thermal reserves, which is why you can be so far north. You’re roughly 400 and something, not 500, but you’re a lot of miles north of Chicago and Milwaukee. Even though you’re more north than Chicago and Milwaukee, you never have that blistering cold weather–

Fraser: Yeah.

Dr. Gay: – those two cities get.

Fraser: Yeah, and thanks to being beside the ocean. So, normally – just in a normal year, all these things are in lockstep. Occasionally, I remember – what was about three or four years ago – Susie will tell exactly; when they were getting like -10° in Atlanta, where she lives. It was just mayhem, and same situation. That’s normally a very warm place, and so you got another situation where the polar vortex had fragmented and moved around.

So, let’s address the elephant in the room. People have said, where’s our global warming? Everything is so incredibly cold. This is because of global warming, right? This is a result of climate change.

Dr. Gay: This is where we have to remember–

Fraser: Maybe, probably.

Dr. Gay: No, it is– it flat out is. The science of this is that as the average temperature of the planet increases we’re seeing the ices that normally cover the Arctic sea or melting. Instead of reflecting light back up away from our world in wavelengths of light that are happy to radiate away, instead, the heat is getting sucked into the oceans that are no longer capped with that wonderfully reflective ice.

The oceans are warming up; they’re radiating infrared, which does not escape through our atmosphere, and so instead of having this wonderful cold area that is reflecting all the warming light away, the ocean is absorbing the heat. The same is happening with the land. We’re also seeing the permafrost, the tundra – these areas of frozen Siberia, Alaska – these areas are melting, and so now the ice reserves, the temperature reserves of coldness in the soil is also going away.

So now, we have heat being trapped in the land, we have heat being trapped in the ocean. We generally see the polar vortex lessen in summer. We always have seen, since we had satellites in the air, that some of the Arctic sea broke up in the summer. During the same period, we’d see the jet stream become more erratic in its behavior.

Dipping down further towards the south, and that jet stream ducking southward is a sign of a polar vortex that is no longer tightly confined; that has weakened, and fragmented. And, one would think this is if you’ve seen hurricane images. As that hurricane deteriorates into a tropical storm, it fragments into multiple pieces, and you can still see hints of the structure in that tropical storm. But, it’s only when it’s a fully formed cyclone, that you have that beautiful spiral structure.

The polar vortex is actually a cyclone of air movement. It’s just not a storm movement, but it has the same physical structure. When the needed conditions aren’t there, it fragments into multiple pieces. Just like as that hurricane turns into a tropical storm, you’ll get bands of rain going in all directions.

When the polar vortex fragments, you get blobs of cold air going in various directions. It all comes down to what the thermal gradient is. Right now in the winter, we’re not seeing that completely frozen terrain; we’re not seeing completely frozen Arctic sea. This means we don’t have that amazingly cold, thermal gradient that amazingly strong vortex of cold air. Instead, we have this fragmenting system.

Fraser: Right. For the people who are like, “Boy, I sure wish we could have some global warming right now.” Don’t worry, in the summer time everything will be on fire, and there’ll be horrendous droughts. So, it’s these extremes, now. Where you get you get a winter that doesn’t behave like a winter is supposed, and you get a summer that doesn’t behave like a summer is supposed to and the two go hand-in-hand.

So, we freaked out about global warming and climate change in other episodes, so you know we’ll save that for a future episode. So, let’s talk more about some of the science of these polar vortices, because we find these across the solar system. What are some other places where we see these polar vortices?

Dr. Gay: Venus is one of the more intriguing ones, because it doesn’t have just a single polar vortex, per pole, like we have here on earth. Rather, this slowly, slowly rotating world. It still has the effects that lead to a polar vortex, but it actually is a double vortex at its pole. Now, this is where it’s important to remember that cyclones are caused by two air masses at two different temperatures; one cold, one hot and that freezer analogy you gave of you open the door and you feel the cold air get displaced out towards you as the hot air rushes in.

Now, in that case you this linear exchange of temperatures. With a rotating planet, the Coriolis force is like, “No, I’m gonna make you rotate,” and that Coriolis force is what drives hurricanes; what drives the polar vortex to move the way it moves, and to give us the spiraling storm patterns. If you look at the current images coming down off of satellites like the Terra satellite, showing amazing storms coming off of the Great Lakes region.

Now, with Venus you still have–

Fraser: Yeah.

Dr. Gay: – the Coriolis force. Because, it is still rotating, but it’s day is longer than its year; and this super slow rotation means that the Coriolis force is like, “I think I’ll rotate. I think I will do something,” and it doesn’t lead to this tightly focused storm such as we see here on earth, on top of both of our poles. They instead, and with this super cooled, double vortex.

Fraser: There isn’t anything right now, but we got some pretty great photos that came from the Japanese spacecraft that at Venus ,right now. I can even say it, Akatsuki?

Dr. Gay: I’m gonna let you do that.

Fraser: Yeah, I’m sure someone is gonna fix that. But, you’ve got this – you can’t see it in the visible light. Here, you can see the cloud movements, and you can see with visible light, but with Venus you need to use infrared–

Dr. Gay: Yeah.

Fraser: –to be able to peer through these really thick clouds, and you get these – just these amazing, as you said, double polar vortices that, sort of, go around each other with all these other high-level clouds that are swirling around it. So, for the longest time– my dog is freaking out upstairs. I apologize for anyone who can hear this.

We thought that Venus was just dull and bland; that everywhere on the entire planet was the same temperature, and it is. But, there are still, in the upper cloud tops is really great movement and it’s still because Venus is turning. It has a tremendous atmosphere, and you get these motions. But, the coolest ones are on, I think, Saturn.

Dr. Gay: Yes. So, Saturn’s we can’t fully explain. Because, they’re actually hexagonal in shape. Where there are standing waves, as best we can tell, built up that cause essentially, flat sides going around the eye of the vortex. Here on Earth, we can’t generally just look at a pole and go, “Yes, there’s a polar vortex.” Because, it’s clear air that happens to be moving. You can’t see the wind unless there are clouds in it.

Cold air on earth over the poles is super dry. It’s only when that cold air sweeps across, for instance, the Great Lakes and picks up moisture off the Great Lakes, and then buries Ohio that that lake effect snow of the dry air going over a warm body of water, picking up the moisture, dumping the moisture; then we can see it.

So, these Terra images we’re seeing allow us to see the cold air picking up the water, clouds forming. While, on worlds like Venus where you have clouds everywhere; on worlds like Saturn and Jupiter where you have clouds everywhere, the exact structure of these polar vortices is obvious in the images, without having the model out the winds.

Venus, you have to look at different wavelength, but with Saturn, it’s just there, in visible light. Actually, allowing you to look down the eye of this polar cyclone and see deeper into the layers of this world’s atmosphere.

Fraser: I’m putting – for the people who are watching the live show – I’m just putting up a picture of it, beside you so that they can see what this looks like, and it is just the weirdest. It’s the weirdest thing, because it is absolutely this hexagonal shape with swirling clouds, and tiny storms, and then in the middle it just goes down to this–

Dr. Gay: Hexagon.

Fraser: Yeah, yeah, the hexagon. You say it’s a mystery. Right, we don’t know completely–

Dr. Gay: There’s lots of conflicting theories. The words “standing wave” is used pretty consistently. So, whatever the physics is, it involves probably something that generates standing waves.

Fraser: Right, and people have been able to sort of simulate this. You’ve probably seen this at a science center where you take this big disc with some kind of material inside of it, and you spin it–

Dr. Gay: Yeah.

Fraser: – and you get these interesting shapes in that; from these fluids turning–

Dr. Gay: Yeah.

Fraser: – of different densities, and so on. So, there is something going on, as you said, a standing wave that has something to do with densities and different kinds of fluids. We see something kind of analogous on Jupiter as well. I think it has its own version of its own–

Dr. Gay: Yes, and we even actually see this on Mars, sometimes. Hubble has been able to image colossal polar clouds over the poles on Mars that shape out vortices. Here again, we have to wait for there to be clouds in the right place, but Mars with its atmosphere does sometimes put on a show.

Fraser: I’ve got a research article here talking about the stability of Mars angular polar vortex. Of course, they’ve got 1% the atmospheric density that we have here on Earth. So, there’s only so far that you’re gonna get. Would you expect to find this on Titan? Literally, any place that is rotating with an atmosphere you would expect to find this kind of a structure.

Dr. Gay: It all comes down to how much of a temperature gradient do you get. With Titan, what I don’t know is how the interplay of reflected light off Saturn, of its extreme distance from the sun, its small size, its tilt; I don’t know how much that will drive vortices. So, if it has them, they’re probably – I’m not going to say probably. I don’t know they could be wussy, they could be strong. It all depends on how all these different factors interplay

What’s interesting is most of the worlds we’ve talked about, you have cold polar vortices, because the pole isn’t exactly pointed towards the sun, in general. And it’s at such a great angle, that the light does hit it is coming in at a severe angle. When you look at these convective cells, the numbers of the convective cells are such that, the pole is cold.

But, Saturn likes to fool us; and Saturn with its hexagon, it’s the only warm polar vortex that a world has. So, the question becomes, as we look at worlds and we go from planet to moon; are we going to find cold or warm? These are things that as people pour through all of the Titan data, now that Cassini’s over; what are they going to piece together and find?

Fraser: In one of my sadnesses, is that we don’t have any spacecraft at Uranus and Neptune.

Dr. Gay: Yeah.

Fraser: I would assume, that both of these will be absolutely fascinating for future observations. Because with Uranus, the whole planet has rolled over on its side–

Dr. Gay: Yeah.

Fraser: – and it spends half the year with one pole facing the sun and then half of its year with the other pole facing the sun. What must that do? Where the rotation is perpendicular to the way it’s being illuminated from the from the sun, that must create some really bizarre atmospheric effects.

Dr. Gay: Coriolis effects. Yeah.

Fraser: Yeah, we see some of the storms on Uranus, but we really do need in order to hang out there and spend a long time, being able to orbit it. Of course, even just by following it on the plane of the ecliptic, it should come naturally into a nice polar orbit that would allow it to go around and see the North Pole and the South Pole, and the North Pole and the South Pole.

Then, you get Neptune which is farther out, colder, receives less heat from the sun. What kinds of atmospheric stuff are happening there? All we see is, we got a couple of images that were taken by the Voyager spacecraft, and the best of the Earth-based telescopes, can do. Those would be ideal places to go and understand.

Dr. Gay: With Uranus, we just never get to see that far side that is not pointed at the sun. The orbits don’t let us get there, from here. Unfortunately, right now the energy that the Delta-v required to go from on your way out to Uranus and Neptune, to then, going from going towards it now being in orbit around it. That’s a huge Delta-v.

No one’s been willing to build the spacecraft that has the capacity to do the Delta-v for a get there quickly, and no one has the patience to build one for the get there slowly and require less energy to get into orbit.

Fraser: Right, yeah. I reported on this several times. There are a couple of proposals in the works. Let’s talk a bit about extrasolar planets. Because, what were really finding with our discoveries thanks to Kepler, and now Tess, and all of the other spacecraft is just the extremes that are out there. Would we expect to see extreme versions of polar vortices from some of these worlds? I’m thinking about things like, hot Jupiter’s and things that are tidally locked to their to their stars, and things like that. What kind of unusual situation could we expect to see?

Dr. Gay: I have a light. I have a light, so I can really do this demo well. So, if you have a rotational axis that is pointed towards your star, you probably gonna end up with something weird doesn’t involve strong polar vortices. If however, you are perpendicular to your light rotating around rapidly, so, more rapidly than we generally see.

So, Jupiter has roughly a nine-hour. Saturn, is again several hours, in rotation. These rapidly rotating worlds see very strong polar vortices. So, imagine having an earthlike world that’s rotating much faster. It’s going to have much stronger polar vortices. It’s going to have much stronger Coriolis forces, and that starts to get much more exciting. Perhaps, more exciting than you might wish to live on.

Fraser: Yeah, yeah.

Dr. Gay: But, I’d still like to see that.

Fraser: And, then you all to imagine those worlds. For example, water worlds, where they have no continents. The planetary bands can go all the way around the planet. But, you would almost expect then, the puller vortices to be very well behaved

Dr. Gay: Yes.

Fraser: Because, you’re not getting get these changes. You’re getting a lot of movement, north or south, as the as the jet streams attempt to move around–

Dr. Gay: This is exactly what we see on Jupiter.

Fraser: Yeah, yeah. Perfect bands in opposite directions; side by side by side, chopping up the planet into little slices.

Dr. Gay: It’s our silly mountains and landscape that makes it so hard to predict the weather.

Fraser: So, we could have a nice dependable winter weather system, if we flattened all the mountains?

Dr. Gay: And, made sure that the temperature gradients were constant.

Fraser: Filled in the oceans, flattened of the mountains, and just made everything perfectly the same.

Dr. Gay: I think this is something that we just need to get on.

Fraser: Yeah, all right. We’ll put that in our list of geo-engineering suggestions.

Dr. Gay: Okay.

Fraser: All right. Thanks, Pamela. Enjoy the warmth.

Dr. Gay: I am. I really am.

Fraser: We’ll talk to you next week.

Dr. Gay: Bye-bye.

Announcer: Thank you for listening to Astronomy Cast, A non-profit resource provided by the Planetary Science Institute, Fraser Cain, and Dr. Pamela Gay. You can find show notes and transcripts for every episode at Astronomy Cast. You can email us at info@astronomycast.com, tweet us @AstronomyCast, like us on Facebook, and watch us on YouTube. We record our show live on YouTube every Friday at 3:00 p.m. Eastern, 12:00 p.m. Pacific, or 1900 UTC. Our intro music was provided by David Joseph Wesley. The outro music is by Travis Searle, and the show was edited by Suzie Murph.

[End of Audio]

Duration: 29 minutes
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