This message comes from Amazon One Medical.
When you're sick and your doctor can't see you for three weeks, well it might as well be three years.
Amazon One Medical has 24 -7 virtual care.
They know that colds can't wait.
Healthcare just got less painful.
Amazon One Medical.
You're listening to Short Wave from NPR.
Hey short wavers, producer Burle McCoy in the host chair today.
So every couple of years when I was growing up in the suburbs of St. Louis, Missouri my family and I would gather in our basement not for a party or game night but to take cover from a potential tornado.
As a kid living around tornado alley I thought this was normal.
If you're unfamiliar, Tornado Alley is just a seasonally shifting section of the US that gets a high level of tornadoes.
But I later learned that people who live outside of this area don't experience nearly the same amount of tornadoes.
It is really the global hotspot of tornadoes.
That's Sushmina Partak, a freelance science journalist who wrote about the science of tornadoes for the publication EOS.
And she says, the reason this region has at least 10 times more tornadoes than any other place in the world, is clear.
You have to blame geography for that.
So, tornadoes form from thunderstorms. And for them to do that, different types of winds need to blow at different temperatures in different directions.
You need cold, dry air coming in from one direction.
Like from the Rocky Mountains.
You need warm, humid air coming in from one direction.
Like the air coming up from the Gulf of Mexico.
And you also need like these strong gusts of wind that are a little bit higher up in the sky, that kind of like exert that force.
These winds moving at vastly different speeds and directions are called wind shear and they can lead to rotation within the thunderstorm.
So now you have a spinning column, a rotating thunderstorm, and if the conditions are right, that rotating column can stretch to the ground and that's how you have a tornado.
Technically, tornadoes can happen anywhere in the world and have been recorded on every continent except Antarctica.
But even taking into account the cold air from the Rockies and warm air from the Gulf, scientists still wondered why there were so many more tornadoes in Tornado Alley than anywhere else around the globe, especially considering Tornado Alley is very similar to a section of South America, at least geographically.
So the question researchers really had was like, if there's this like similarities and geography of these two continents, why doesn't Central South America have a tornado alley?
Today on the show, new research on why the US gets so many more tornadoes and what the findings might mean for reducing them in the future.
You're listening to Short Wave, the science podcast from NPR.
Support for NPR and the following message come from Betterment, the automated investing and savings app.
CEO Sara Levy shares how Betterment utilizes tech tools powered by human advice.
Betterment is here to help customers build wealth their way.
and we provide powerful technology and complete human support where technology can deliver ease of use and affordability and the people behind that technology can provide advice and guidance.
Learn more at Betterment .com Investing involves risk.
Performance not guaranteed.
This message comes from Amazon Health.
Have you ever been so sick that even the thought of standing up to go to the doctor made you even more sick?
Amazon One Medical has 24 -7 virtual care so you can get help while horizontal.
And with Amazon Pharmacy you can get medicine delivered fast right to your door.
You just have to make it to your door.
Thanks to Amazon, healthcare just got less painful.
Okay, Sushmita, let's talk about the research you reported on.
It was done by a scientist named Fooning Li when he was at MIT.
And Fooning and his colleagues studied tornado occurrence by using this historical data to model and simulate the interaction between land and the atmosphere.
Tell me about what they found.
So, so the starting point of their research was really like the geographic setup in Central North America and Central South America is kind of similar, but South America does not get as many tornadoes, even near as many tornadoes as North America does.
And so, they really wanted to figure out why there was this huge contrast. And what they found was, it was because of a surprising new ingredient, which is the roughness of the land surface many, many thousands of away from where the tornadoes were actually happening.
So when the easterly winds are coming over the Gulf of Mexico towards Central North America, Tornado Alley, that's a relatively smooth surface, like this vast expanse of ocean.
So, you know, winds don't really encounter any resistance.
They can, you know, build up a lot of speed and that's really important for wind shear, which is very important for tornado formation.
But in South America, what happens is those easterly winds are blowing over the Amazon rainforest. So you have a lot of vegetation, a lot of hills, so a very rough surface.
And because of this rough surface, the winds get broken down.
And so the tornado potential also gets suppressed.
Wow, so it really is like this big picture geographical reason for why there's a different amount of tornadoes in North and South America yeah and so it's it's really just like if you you have flat or you have not flat that's the big factor yeah and we upstream yeah and upstream being different for North and South America?
Oh just the region near the Yigw Northwest from where the easterly winds are coming in to those regions okay so is it like coming from the south in the northern hemisphere and coming from north and the su...
okay, okay. And to test this sort of hypothesis and to arrive at their findings, the researchers tested this out in a global climate model, which is like a computer simulation of the Earth.
You know, scientists use it all the time to learn about climate patterns and figure out how they'll change in the future.
So in this global climate model, you can sort of tweak different parameters to see how things will change.
And so what the scientists did was they replaced the Gulf of Mexico with forests to make it kind of rougher.
And when, when they did that, they saw that tornado potential in the US in Tornado Alley, it went down.
And similarly, when they smoothed out the Amazon forest, tornado potential in Central South America went up.
And I say tornado potential here, because the model cannot produce tornadoes exactly.
It can only simulate the environment, the instabilities that lead to a tornado.
So that's just a small but important caveat.
Okay, and speaking of caveats, this I mean, this research seems like it's pretty straightforward, pretty solid.
Yeah, it is. It is pretty solid.
And I asked another scientist who is not part of the research about limitations.
And she was like, this, this, this feels like a pretty solid study.
And actually she studies how land cover in the vicinity of the storm, like a mile or two miles radius of the storm changes tornadoes.
And so she was actually surprised, she was actually very fascinated by this, that land cover and terrain so far away from the actual storm can also affect tornado potential.
Okay, so it's like people hadn't thought to look this far upstream.
And how far are we talking?
We're talking about hundreds of miles away from where the tornadoes are actually forming, from where the storms are actually forming.
Wow. So the researchers did this work, solved kind of a big mystery in why Tornado Alley gets so many tornadoes, what could be some implications of their research?
There aren't a lot of implications, because, you know, we as humans do a lot of things that can change the roughness of the terrain.
Like when you cut down forests, it's like smoothing out the surface.
that's already happening in the Amazon with deforestation, or when you set up large -scale wind farms on a vast platypus, it can make the overall surface rougher.
That's happening in the Midwest. So the authors of the study really want to, bring attention to this point that, there are a lot of different things that affect tornadoes and that lead to tornado genesis.
And one thing that's not been looked into until now is this large scale surface roughness or the roughness of the terrain, very, very far away from where the storms are forming.
So this was a big takeaway.
And then I know climate change is linked to increases in extreme weather.
So heavy, extreme rainfall, heat, drought.
And I've read that last year it was actually the second most active tornado season in recorded history.
Wow. Do scientists expect instances of tornadoes to change as our climate warms?
So the short answer is we don't know how climate change will affect tornadoes.
Now, research does suggest that we'll have more storms in a warmer world.
And there are some studies that suggest that climate change may be shifting tornado alley in the U .S. towards the east, but tornadoes are very complex. they are so unpredictable and they are so complex that it's hard to attribute changes in tornadoes to climate change.
It's, you know, very easy to say, oh this, this heat away was caused because of climate change, or this like really heavy spell of rain can be attributed to climate change.
But you can't do that very easily with tornadoes.
And they're also still kind of mysterious.
Like we don't fully understand what factors have to come to play in what exact measures for a tornado to form.
So all this makes it hard to establish a clear definite link between climate change and tornadoes.
But that said, I think in order to understand how climate change will affect tornadoes, we have to first understand how tornadoes are formed and what leads to a tornado hotspot.
And the findings of this study get us a little bit closer to that.
And so I think going forward, I think a broader takeaway is that when we think about how a changing climate will affect storms in general, including tornadoes, we should not only think about rising temperatures but also changes in terrain because that also affects storms and severe weather.
Sushmita, thank you so much for coming on the show to talk to us about tornadoes.
Thank you so much for having me.
Short waivers will drop a link to Sushmita's full article in our episode notes.
And if you liked this episode, please follow us on the podcast platform you're listening on.
It really helps our show.
This episode was produced by me, Burleigh McCoy, and edited by our showrunner Rebecca Ramirez and by Jeff Brumfield.
Tyler Jones, check the facts and Quaise Lee was the audio engineer.
Beth Donovan is our senior director and Colin Campbell is our senior vice president of podcasting strategy.
I'm Burleigh McCoy.
Thanks for listening to shortwave from NPR.
This message comes from thrive market.
The food industry is a multibillion -dollar industry, but not everything on the shelf is made with your health in mind.
At Thrive Market, they go beyond the standards, curating the highest -quality products for you and your family, while focusing on organic first and restricting more than 1 ,000 harmful ingredients, all shipped to your door.
Shop at a grocery store that actually cares for your health at thrivemarket .com slash podcast for 30 % off your first order plus a $60 free gift. This message comes from Thrive Market.
The food industry is a multi -billion dollar industry, but not everything on the shelf is made with your health in mind.
At Thrive Market, they go beyond the standards, curating the highest quality products for you and your family while focusing on organic -first and restricting more than 1 ,000 harmful ingredients.
All shipped at your door.
Shop at a grocery store that actually cares for your health at thrivemarket .com podcast for 30 % off your first order plus a $60 free gift.
