Gravity Waves … not gravitational waves … move atmospheres and make pretty clouds.
Show Notes
- Introduction to Atmospheric Gravity Waves:
- Definition and differentiation from gravitational waves.
- Their occurrence due to a balance of buoyancy and gravity.
- Observations of Gravity Waves on Earth:
- Descriptions of how these waves manifest in cloud formations.
- Observation of gravity wave clouds in Florida and Illinois.
- Implications of Political Turbulence:
- Brief discussion on how political changes in the U.S. could affect science communication and research collaborations.
- Gravity Waves Across the Solar System:
- Mars: Observations from both ground and orbit, and their role in Martian atmospheric dynamics.
- Pluto: Gravity waves observed in Pluto’s atmosphere, visualized in images from the New Horizons mission.
- Venus: The massive waves driven by the planet’s fast-moving atmosphere as seen by Japan’s Akatsuki spacecraft.
- Mechanics Behind Gravity Waves:
- Factors influencing gravity waves, such as smooth air layers and displacement triggers like mountains or temperature changes.
- The role of these waves in the vertical and horizontal transport of atmospheric material.
- Unique Triggers for Gravity Waves:
- Discussion on rare triggers like total solar eclipses causing gravity waves.
- Gravity Waves Beyond Earth:
- Examples of gravity waves in the atmospheres of other planets like Jupiter, Titan, and Neptune.
- Spiral Arms of Galaxies:
- An analogy to how spiral arms in galaxies are a form of gravity wave.
- Interesting Tidbits:
- Gravity waves have been detected in a variety of contexts, extending our understanding of dynamic processes in planetary atmospheres.
- Despite the complicated nature of these phenomena, they share common principles across different celestial environments.
Transcript
AstroCast-20250203.mp3
Fraser Cain [00:00:48] Astronomy Cast Episode 742, Atmospheric Gravity Waves. 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. I’m the publisher of the universe today. With me as always is Dr. Pamela Gay, Senior Scientist for the Planetary Science Institute and the Director of CosmoQuest. Hey, Pamela, how are you doing?
Pamela Gay [00:01:10] I am doing well. I went from being very cold in Florida to not being very cold in Illinois. I think at some point, maybe I’ll be warm again, but wow, the winter this year is very determined to get its presence known. How are you up there in Canada?
Fraser Cain [00:01:32] Great. We had been unseasonably warm. I could have grown citrus here warm. We didn’t dip below freezing for more than a couple of days, barely. Then a cold snap just came in, but still, it’s just barely below freezing. Apparently, next week we should get the polar mass is going to move our way and then we should get a little more seriously cold. Although Vancouver Island seriously cold is negative 6 Celsius. I don’t know what that is in the 20s, I guess. It’s not too bad. Nothing is cold as Florida or Louisiana where you see snow and stuff. I think it’s important for us to just warn people that both you as a running CosmoQuest and such and me as a Canadian are about to go through an enormous amount of turbulence with all of the stuff that’s going on politically in the US.
Pamela Gay [00:02:38] We’re sorry.
Fraser Cain [00:02:39] Yeah. For you, you’re having to deal with the repercussions for the people you can hire, the programs that you can apply for, all of the grants you’ve applied for are all getting reevaluated, shut down, closed off. I’m about to go into a trade war with you. We are now enemies, which is going to suck. I don’t know what the repercussions are going to be and what the implications are going to be for our ability to hire Americans, which I hire a bunch of Americans, so that may have to change our coverage. I don’t really know what the ramifications are. We’re going to see how this goes. I just want to warn everybody listening to this in advance that you could see disruptions in our programs, in what we do. It’s just going to be us attempting to navigate what is now a much more complicated and uncertain time in what we do. I’m sure what I’m explaining to you is a conversation that you’re having across all of your organizations and companies and nations and all of that as we chart this path forward. For all of us, I hope we’re able to make this uncomplicated and undisruptive as humanly possible so that people can just watch the shows they like and enjoy the science. They do their science and get work done as friends.
Pamela Gay [00:04:15] All we want to do is communicate science. This shouldn’t be controversial.
Fraser Cain [00:04:20] Yeah, exactly. Have you ever looked up into the sky and seen bizarre cloud formations that look like waves on the ocean? These are gravity waves, and not to be confused with gravitational waves. They’re caused by a balance of buoyancy and gravity. Of course, these have been seen across the solar system. We will talk about it in a second, but it is time for a break. I think I just won my taxes.
Pamela Gay [00:04:46] Yeah. I just switched to H &R Block in about one minute. All I had to do was drag and drop last year’s return into H &R Block and bam, my information is automatically there. I don’t have to go digging around for all my old papers to switch? Nope. Sounds like we just leveled up our tax game.
Fraser Cain [00:05:03] Switching to H &R Block is easy. Just drag and drop your last return. It’s better with Block. And we’re back. Do you have your classic favorite? Do you have times when you’ve seen
Pamela Gay [00:05:19] gravity waves? I sure have. Yeah. We live in a very flat part of the United States, a very, disturbingly flat part of the United States. And because of that, we get these nice, stable air patterns that when something disrupts them, it will cause clouds to form in this set of stripes across the sky. And those stripey clouds are driven by gravity waves. And this entire episode is actually inspired by the fact that last Friday, it was finally sunny in Orlando, go figure. And I drove out to Cape Canaveral because I wanted to get some pictures of the new Blue Origin facilities. And there was this amazing set of contrails radiating away from a point on the horizon. And one of these contrails was perpendicularly by a bunch of gravity wave clouds. And it was just the wildest thing. And so I’m like, okay, let’s talk about this because clouds can get formed by so many different things. And gravity wave clouds are found throughout the solar system and probably throughout the universe. We just don’t have evidence of that. And they’re cool.
Fraser Cain [00:06:43] Yeah. Yeah. And so like where I live, it’s the opposite of you. I live on the eastern side of Vancouver Island and we have a mountain range to the west of us. And so you’ll get these low cloud formations that will be passing over the mountains. And it’ll almost be like waves on the sea that you can see where the air mass is oscillating as it’s going up and down. And as it goes down lower, you get this condensation and then it goes up a little higher and then you don’t get any condensation and you get these just these weird clouds that roll. We see them all the time in certain times of the year when the conditions are right. In the springtime and in the fall, we get these big fluffy, what you would think are cumulonimbus clouds. They look like giant storm clouds, but they’re not. They don’t harken rain. But at other times of the year, yeah, we get these really weird cloud formations and it’s pretty cool.
Pamela Gay [00:07:48] That is excellent. And that’s the thing about gravity wave clouds is they’re driven to expand on what you said with buoyancy versus gravity by having nice, smooth layers in the atmosphere. And then something comes along and displaces one of those layers and it sets up a harmonic oscillation. And that harmonic oscillation of something rising and falling, falling too far and rising back up, that harmonic oscillation is what can drive these clouds. And when you have a nice, calm set of layers that then hit the top of a mountain, in your case, are disrupted by a temperature variation or something like that in my area, whatever it is that drives that localized instability, it then expands out and causes all these amazing clouds that we then see.
Fraser Cain [00:08:56] So what are the factors that will tell you whether or not you’re going to get this kind of an atmospheric effect?
Pamela Gay [00:09:04] So you can’t generally find them directly under the jet stream. There is just way too much turbulence going on. You need to have smooth, stable layers. You’re not going to find them at where a front has just gone through where everything is turbulent. You’re not going to find it over an area with a lot of thermal instabilities. You need to start out from the position of nice, smooth air, the kind of conditions that you want if you’re out flying an airplane, something without turbulence. And then in these nice, smooth conditions, you need something that is going to cause a displacement in the atmosphere. So the air hitting a mountain will do it.
Fraser Cain [00:09:52] Like a trigger mechanism.
Pamela Gay [00:09:53] You need a trigger mechanism. My favorite trigger mechanism is something that was theorized for decades and wasn’t seen actually until just a few years ago. And this is total solar eclipse driven gravity waves.
Fraser Cain [00:10:09] What?
Pamela Gay [00:10:09] Yeah. Yeah. This is one of those things that you have to be able to just launch weather balloon after weather balloon after weather balloon starting a few hours before the solar eclipse, ending a few hours after preferably like 12 hours before 12 hours after. And gravity waves will already be forming off and on if the conditions are right. But when the conditions are right, having the shadow, which is a sudden change in temperature sweep through is going to cause a rapid density change in the atmosphere. And that density change is a triggering mechanism. So you have air that was nice and warm in sunlight, suddenly in shade, in getting lower density. That displacement will drive horizontally moving gravity waves that propagate in the direction that the solar eclipse is moving across the planet.
Fraser Cain [00:11:12] It’s really cool. So, you know, you talked about how these can be seen on other worlds in the solar system. So where do we see these kinds of events across the solar system?
Pamela Gay [00:11:29] The best picture I’ve seen captured of them is actually Pluto’s super, super thin atmosphere. So do you remember when we got those images that had the atmosphere not quite backlit, but kind of backlit? We could still see a crescent Pluto and there were these haze layers in the atmosphere. Those haze layers were caused by the propagation of gravity waves vertically through the atmosphere.
Fraser Cain [00:12:05] I thought I had given you a softball and I thought you were going to talk about a different planet, but some images that I’ve seen, but absolutely. That’s great. I hadn’t even thought about those.
Pamela Gay [00:12:18] That was a softball. I mean, it’s an amazing, stunning image. Pluto, yes, it has amazing topography, extremely high highs, extremely low lows, but its atmosphere doesn’t have a whole lot to displace it. And so it’s able to get these waves setting themselves up in the atmosphere.
Fraser Cain [00:12:43] All right. We’re going to talk about this some more, but it’s time for another break. And we’re back. So the image that I was thinking of was some of the stuff we’ve seen on Mars.
Pamela Gay [00:12:57] Okay. So Mars has all sorts of different gravity waves going on. They have spotted them in a variety of the different levels of the atmosphere. They have started to figure out that it’s gravity waves that are allowing effects from the lower atmosphere to propagate up to the upper atmosphere. There have been pictures from Curiosity of clouds with that distinctive set of troughs and peaks that are running parallel to each other for basically from everywhere you look out to the horizon. Gravity waves are just like another day in the Mars atmosphere. And it’s amazing that we know that the science here works on other worlds, but then Mars has just such a thin atmosphere that it’s amazing that we can see these effects in its clouds and we can.
Fraser Cain [00:13:55] Sometimes I, you know, I mean, we are a video podcast because we record on YouTube, but it would be great to show people like images. So if you’re like in front of a computer, do a Google search for gravity waves Mars, and you’ll see just these incredible images of what really looked like ocean waves in the cloud structures on Mars. And as you said, you know, these have been observed from the ground from Curiosity, but they have absolutely been observed from above with varying orbital spacecraft. And so what role do we think that these gravity waves have in the sort of evolution of the Martian atmosphere? We know they can go from clear skies all around to global dust storms.
Pamela Gay [00:14:46] So during the Martian winter, they’ve been able to catch these clouds forming directly above Curiosity. Very first winter, it was one of the things that Curiosity caught. We are now realizing this is how lower atmosphere material is able to get pushed up into the upper atmosphere. So one of the things we’ve been really struggling with is how is it that you can have dirt devils, dust devils, whatever you want to call them, and all these low level ground effects, then normal dust storms, and then shoot, there’s dust all the way to the top of the atmosphere. And we’re going to do a separate episode on just everything we now understand about dust storms because it is mighty. I think you actually know more about this than I do right now. So if you can give a summary, that would be amazing. We both read different things.
Fraser Cain [00:15:52] Well, the paper that came out fairly recently was just them starting to understand what are the factors that come together to cause these global dust storms on Mars, because you’ll get regional dust storms, but there’s very weird conditions that end up with you getting this entire global dust storm. And this was the kind of event that killed opportunity. You know, although the wind doesn’t blow very hard, because it’s 1 % the density of the atmosphere, you get this decrease in the sunlight available to the solar panels. The rover was already almost out of electricity anyway, barely able to survive through the cold winter nights on Mars. And so this delivered the death blow as one of these global dust storms. And now it looks like people have done enough modeling of the dust storms on Mars that they’ve been able to realize that it is unseasonably warm conditions that lead to the, it gives you a higher likelihood of the global dust storm forming and going to the entire planet. And so now you can sort of see if you’ve got unseasonably warm temperatures, that’s more likely to lead to these regional dust storms linking up and eventually creating this planet wine storm. So it’s like, the way we described it in the universe today story was if the weather’s nice on Mars, panic, because it’s going to, you know, because the dust storm comes next. So there’s this situation on Mars where we have these diurnal tides. You get this change in the atmosphere between day and night. And then these tides interact with the atmospheric waves. And at different altitudes.
Pamela Gay [00:17:43] And gravity waves in general are most common near the Martian poles. They can occur absolutely everywhere. Curiosity saw them straight above it. But in general, the conditions that are right, the nice stable atmosphere, something causing a trigger, those circumstances are most common along the poles. There’s an article in science about this. I’m going to do something I don’t think I’ve done before on astronomy cast and just read you guys a quote that I love about this. The Martian environment is the exotic wrapped in the familiar. The sunsets are blue, the dust doubles enormous, the snowfall more like diamond dust, and the clouds are thinner than what we see on the earth. And that is from a March 23rd updated article talking about gravity waves. It appears in the journal science. And these conditions are essentially allowing these super thin, all but transparent wispy clouds to have this undulating structure. And that is both you have the horizontal propagation, which is what we’re seeing in the clouds. There’s also vertical propagating gravity waves, which is how things are able to get through the different layers in the atmosphere. And so there’s a lot of complexity going on. And one of the unfortunate things is we don’t exactly have a fleet of weather balloons that we can release from the surface of Mars to study these things in the same kinds of details that we’re just starting to be able to do here on earth. But at least we can image them, even if we can’t directly measure the temperature pressure and humidity variations that are involved in them.
Fraser Cain [00:19:47] All right, we’re going to talk about this some more, but it’s time for another break.
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Fraser Cain [00:20:23] And we’re back. So we talked about Mars, we’ve talked about Pluto, we’ve talked about Earth, but there are more worlds with atmospheres in the solar system. So where do you want to go next? Venus, Jupiter, Titan?
Pamela Gay [00:20:35] I was going to say Venus. So Venus has the biggest waves. The clouds are moving at 100 meters per second.
Fraser Cain [00:20:54] Right. Like it’s important for people to understand it takes four days for the air on Venus, the atmosphere on Venus to rotate once while it takes for the sun to come back to the same spot in the sky. It’s 225 days. It’s like 247 days for Venus to turn once on its axis. But the air turns, the weather turns every four days.
Pamela Gay [00:21:17] 100 meters per second is a kilometer every 10 seconds. That is just like mind -boggling to me. And we can see in images from Japan’s… You’re going to correct my pronunciation. Thank you. Thank you. I didn’t have to say it badly. You just said it. Japan’s Akatsuki spacecraft. Planet C. I’m going to go with Planet C. I can say that. Has been able to pick up these sets of waves that are taking up roughly a third of the planet’s hemisphere that we can see at any given moment or the spacecraft can see at any given moment. And these waves that are taking place in the clouds where you have these winds at tremendous speeds, the waves are stationary. And this is the kind of thing that causes me to think I chose the easier field going into astronomy as compared to meteorology.
Fraser Cain [00:22:30] Right. Was that, sorry, was that like a direction you were thinking of going?
Pamela Gay [00:22:36] No, never. But usually you’re like, I’m an astronomer. I went the hard path. No, compared to meteorology. And no one ever says, this is not rocket science. This is not brain surgery. This is not meteorology. Meteorology is the hardest of all of these folks. So in trying to figure out what’s going on as near as they can tell, the weather patterns going over mountains or as probably it was big old volcano on the surface of Venus was able to trigger an upward propagating gravity wave that created standing waves in the atmosphere. So we are seeing a super complex situation.
Fraser Cain [00:23:32] Yeah, you’ve got these winds whipping around Venus every four days, 100 meters per second. You’ve got what looks like a mountain range in the Ishtar -Terra region of Venus. Yeah. And so as the winds are whipping around, you’re getting this oscillation that gets kicked in and it is a permanent standing wave. And so you think about places, there’s this amazing river in Germany that we saw where the water was sort of going down this sluice gate and it was the standing wave. This was in Munich, yeah? In Munich, yeah. People surf it. Yeah, exactly. I was going to mention the
Pamela Gay [00:24:11] exact same thing. What city was it? Yeah, it was in Munich. That’s right.
Fraser Cain [00:24:15] Right by the Science and Technology Museum. Yes. So people were surfing in this. It’s a standing wave. And so you’ve got this standing wave, this standing gravity wave in the atmosphere of Venus. And it really, again, I wish we could show you pictures, but it looks like someone has kind of wrinkled up a side of Venus to create this standing wave.
Pamela Gay [00:24:39] And it’s that exact same scenario of you have an extremely fast moving fluid. We model atmospheres as fluids. It hits a disrupting surface, the mountain on Venus, the sluice gate under the bridge in Munich. And that disruption creates a wave form that appears stationary, although the molecules that are in it, the fluid is constantly moving. The shape of the fluid is unchanging. And it’s this fabulous combination that on Earth is caused by all the features of the geometry of the water. But on Venus, it’s a gravity wave. It’s a buoyancy versus gravity versus landscape issue. And it’s just amazing.
Fraser Cain [00:25:38] We can rattle off other examples of ones that are seen on Jupiter, on Titan, Saturn, Neptune. Neptune has the fastest winds in the solar system. So these exist across the solar system. But I want to kind of blow people’s minds. And that is something that doesn’t have anything to do with atmospheres, but also has something to do with gravity waves. And that is the spiral arms of galaxies.
Pamela Gay [00:26:01] Oh, I wasn’t planning to go there. But yes, that’s exactly what they are.
Fraser Cain [00:26:06] Right. Yeah. Yeah. So when you look at galaxies and you see the spiral arms, you are looking at gravity waves, standing waves. They are not that the stars themselves are turning around in the galaxy in the shape of that wave. It is this wave of material that is propagating through the galaxy.
Pamela Gay [00:26:28] And it’s disrupting the motions. So the way to think about it, I’m, as always, looking for things to use to talk with my hands. Okay, we’re going to pretend that this pencil case is a fragment of the arm. Sorry, all of you who are listening, a fragment of the arm of the Milky Way. As a star is orbiting along, it has a nice, smooth, stable motion. But as it gets closer and closer to that arm, the gravity of the excess material within the arm will accelerate that star toward the arm. And as the star is trying to come out the other side of the arm on its continual flow, on its continual orbital motion about the Milky Way, the excess mass inside that arm slows it down. So essentially its motion is disrupted by the gravity of the arm. So it gets accelerated in. It lingers in the arm because gravity is not letting it escape. And then it gets out and it continues its smooth motion. And so this kind of disruptive behavior of gravity waves is something we see over and over and over again.
Fraser Cain [00:27:52] All right. Thanks, Pamela.
Pamela Gay [00:27:54] Thank you, Fraser. And thank you, everyone out there. Hugh, right now, your patronage means more than ever before because we’re able to communicate science in this difficult world without having to worry about it because of you. This week, I would like to thank Abraham Cottrell, Alexis, Bore Enthro Lovesvall, Bart Flaherty, Bresnik, Brian Kegel, Bury Gowan, Daniel Donaldson, Dwight Ilk, Felix Gutt, Galactic President, Superstar McScoopsalot, Georgie Ivanov, Greg Davis, Greg Vield, J. Alex Anderson, Jean -Baptiste Le Matenet, Joanne Mulvey, Jonathan Poe, JP Sullivan, Just Me and the Cat, Kim Barron, Larry Dotz, Les Howard, Lou Zealand, Marco Iorossi, Matt Rueker, MHW 1961, Super Symmetrical, Mike Heisey, Paul D. Disney, Paul Esposito, Pauline Medelink, Peter, Philip Walker, Planetar, Rando, RJ Basque, Robert Cordova, Ruben McCarthy, Scone, Sergey Manilov, Simon Parton, Steven Miller, Tim Garrish, and Zero Chill. Thank you all so much for being here, for letting me mispronounce your names, and we will see you next week. Thanks, everyone. See you next week. Astronomycast is a joint product of Universe Today and the Planetary Science Institute. Astronomycast is released under a Creative Commons Attribution license. So love it, share it, and remix it. But please, credit it to our hosts, Fraser Cain and Dr. Pamela on our website, astronomycast .com. This episode was brought to you thanks to our generous patrons on Patreon. If you want to help keep this show going, please consider joining our community at patreon .com slash astronomycast. Not only do you help us pay our producers a fair wage, you will also get special access to content right in your inbox and invites to online events. We are so grateful to all of you who have joined our Patreon community already. Anyways, keep looking up. This has been Astronomycast.