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The Atmospheric Highway · The Climate Translation

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Most of us think of weather as something that moves through, a storm rolls in, and a
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few days later it's gone, a cold snap hits, and then the temperatures bounce back.
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The system feels like it's always in motion.
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But lately, some of you may have noticed something different.
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Heat waves seem to sit in place for weeks to months, rain keeps coming, or winter cold
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snaps occur where Arctic air pushes much farther south than it used to.
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So the question is, is the atmosphere starting to behave differently?
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At the center of that question is something we don't see, but it shapes nearly all of
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our day-to-day weather, the jet stream.
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It's a high speed river of air thousands of miles long that steers storms, controls temperature
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swings, and helps keep weather moving.
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Now, new research is asking whether that river is changing in ways that might make weather
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patterns more persistent and sometimes more extreme.
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Today we're going to take apart what scientists know and what they're debating, and why a warming
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Arctic may be playing a role in how this atmospheric highway behaves.
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Welcome to the podcast, I'm Dr. Mac, and this is the Climate Translation.
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To understand why the jet stream may be changing, we first have to understand what makes
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it work in the first place.
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The earth is constantly trying to balance heat.
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At the equator, the sun's energy is concentrated.
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The air is warm, and warm air is less dense and rises.
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At the poles, especially in the Arctic, there is much less incoming solar energy.
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The air is colder and denser and tends to sink.
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That difference in temperature between the warm tropics and the cold polar regions helps
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to set the entire atmosphere in motion.
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Air doesn't like inbalance.
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It likes to redistribute energy, and one of the most important features that comes out
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of that movement is the jet stream.
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The jet stream is a narrow band of very fast winds high up in the atmosphere, something
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like five to seven miles above the surface.
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The forms along a boundary where warm air to the south meets colder air to the north.
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In atmospheric science, we call this a temperature gradient.
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It's just a difference in temperature over distance.
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The stronger the gradient is, the stronger the winds that form along it.
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Here's a way to picture it.
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Imagine a slope and a stream flowing across it.
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If the slope is gentle, the water flows slowly, but if the slope is steep, the water speeds
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up.
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In the atmosphere, that slope is the temperature difference between the equator and the pole.
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The larger the difference, the steeper the slope, the stronger and faster the jet stream.
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And when the jet stream is strong, it tends to flow in a more direct west to east path
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here in North America.
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That keeps weather systems moving, storms passing through, cold air staying mostly to the
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north and warm air staying mostly to the south.
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This system, as a whole, stays organized.
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Climate change, however, is starting to complicate this system.
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The temperature difference, the slope we just talked about, that gradient.
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It isn't changing evenly everywhere.
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We know the Arctic is warming faster than the rest of the planet.
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That reduces the temperature contrast near the surface between the polar latitudes and
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the mid latitudes and the equator.
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In simple terms, it can make that slope less steep in the lower atmosphere.
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And that has led some scientists to ask an important question.
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If the temperature difference is weakening in some parts of the atmosphere, does that
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also weaken the jet stream?
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And some research is suggesting it can.
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A weaker jet stream can become more wavy.
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Instead of flowing in a relatively straight line, it starts to bend north and then bend south
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in larger loops.
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And those bends can slow down, allowing weather patterns to linger longer in a region.
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But at the same time, other research points to something different happening higher up
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in the atmosphere.
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Changes in temperature at higher altitudes may actually strengthen winds in those upper
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layers.
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So it's a really complex picture.
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Parts of the atmosphere engine may be weakening, while other parts may be strengthening.
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And that's why it's not a simple story.
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The structure of the system is changing, but when the structure changes, the behavior
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can change as well.
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And that's caused many scientists to wonder just how stable jet streams really are.
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So we have this interesting situation.
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Parts of the atmosphere engine may be strengthening, especially higher up.
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But at the same time, we're seeing evidence that the jet stream may be behaving more unevenly.
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So what's going on?
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This is where we need to talk about something called Arctic amplification.
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If you remember something from earlier episodes, The Frozen Vault, the Arctic is warming faster
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than the rest of the planet at about three to four times faster in recent decades.
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And that's important because, as I said, the jet stream is driven in part by the temperature
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difference between the cold Arctic and the warmer regions to the south.
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So when the Arctic warms faster than everything else, the difference starts to shrink.
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Let's go back to that slope analogy.
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If the slope becomes less steep, the flow can slow down or become less stable.
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Now scientists are starting to ask an important question.
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If the temperature contrast is weakening near the surface, could that affect how the
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jet stream moves over time?
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Instead of flowing in a relatively straight west to east path, the jet stream can slow
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and begin to develop large, north, and south swings.
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In atmospheric science, we call this meridional flow, a pattern where the jet stream bends
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and moves dramatically towards the north and then towards the south.
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And when those bends get larger, the system can slow down and in certain situations, those
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waves can linger, and when they linger, so does the weather underneath them.
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So instead of a storm passing through in a couple of days, you might get several days,
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a week, maybe even longer, of the same conditions.
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A heat wave that holds in place, a stretch of heavy rain that keeps returning day after
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day after day, a drought that intensifies over months, or in winter, a jet stream dip
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that allows cold Arctic air to move much farther south than what we would expect.
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You've probably seen the headlines about this.
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The polar vortex outbreaks, or Arctic air plunging into the southern United States.
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What's happening is that the pattern that usually helps contain that cold Arctic air may
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at times become distorted.
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Now this is an active area of research.
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Scientists are still trying to study how strong this connection is, how often it happens,
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and how it interacts with other parts of the climate system.
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But what we're starting to understand is that a rapidly warming Arctic is changing the
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temperature structure of the atmosphere, and that change is influencing how the jet
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stream behaves, especially in terms of how much it bends, and how long certain patterns
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stick around.
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So we've built the pieces.
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We had this atmosphere highway, this jet stream, that usually keeps weather moving.
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We've talked about how that flow can become wavy and uneven.
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Let's talk about what happens when that highway slows down, or even backs up in certain
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areas.
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In climate science, we call this blocking.
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An atmosphere block is a pattern where the jet stream forms a large, stable loop, and
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instead of continuing to move weather systems along, it holds them in place.
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Imagine you're driving on the interstate, everything's moving normally, cars are flowing,
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maybe a little faster, maybe a little slower, but you're getting to where you need to go.
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Then suddenly you see brake lights, quickly the traffic begins to slow.
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What a blocking pattern does in the atmosphere, parts of the jet stream can slow down,
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enough that the weather patterns that are moving through get stuck.
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Consider the Mississippi River.
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In the north, the river is more straight, and water flows quickly and easily.
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But as it travels south, and the ground becomes more flat, it begins to meander and form
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large loops.
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The water has to travel longer.
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Sometimes it speeds up, sometimes it slows down, it can get stuck in whirlpools and bends
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that change the flow.
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In the atmosphere, flowing air is a fluid as well.
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It can also form bends and loops, slow down and speed up.
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And these are the waves that we see in the jet stream.
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Depending on where you are relative to those bends and waves, you can experience very different
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weather.
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If you're under a ridge, a northward bulge in the jet stream, you can get sinking air.
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That can lead to clear skies and lots of sunlight, but can also lead to heat building day after
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day.
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You may have heard this called a heat dome.
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And because that pattern isn't moving, the heat doesn't move either.
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What might have been a two or three day warm spell becomes a month long drought, maybe
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even longer.
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On the other side of that wave, you can have a trough, a dip in the jet stream that
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pulls cooler air southward.
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You can get extended cold spells, especially in the winter because it's not moving out
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quickly like it used to.
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And of course, then there's rainfall.
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If a storm gets caught in one of these slower moving patterns, it can keep pulling in
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moisture from the same source over and over again.
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You can get atmospheric rivers.
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So instead of a storm passing through in a day or two, you can get repeated rounds
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of rain over the same area, over and over day after day.
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That's when the flooding risk really increases because it's raining in the same place for
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an extended period of time.
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Recent research, including studies looking at the winter jet stream behavior, suggests
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that certain patterns have become more variable or more persistent over time.
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In other words, we may be seeing more situations where weather systems tend to linger longer
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than we expected, based on the average in the past.
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But just like we talked about in the last segment, it's still an active area of research.
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Scientists are still working to understand how much of this is tied to Arctic warming,
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how much of it is natural variability, and how much these patterns may change in the
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future in a warming world.
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But what we can say is this, when the jet stream slows down or becomes more wavy, the impact
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can be obvious, longer heat waves, more persistent cold snaps, more atmospheric rivers, storms
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that don't just pass through, but stay.
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At this point, I want to talk about the polar vortex.
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I seem to see something about this every winter nowadays.
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It was brought up whenever there's a major snowstorm moving through, or an intensely
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Arctic air moves into regions that are not used to it.
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But increasingly, it's also being used to discuss why some areas are getting very mild
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winters, or winters where there's little to no precipitation at all.
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Let's define what the polar vortex is.
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What we are describing is a large-scale circulation of very cold air that sits high in the atmosphere
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over the Arctic, especially during the winter months.
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The strongest part of it exists in the stratosphere, several miles above where our everyday weather
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occurs.
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Think of it as a broad region of spinning cold air centered over the North Pole.
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Under normal conditions, that cold dense air stays contained in the Arctic, and one of
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the reasons it stays there has to do with the jet stream.
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When the jet stream is relatively strong and flowing in a more east to west path, it encircles
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this dense air mass and helps to contain it, and keep it largely contained to the higher
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latitudes.
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But it's not a perfect system and it never has been.
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There have always been times when the cold Arctic air pushed southward into the United States
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and a Europe or Asia.
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So when people experienced a cold outbreak, they knew it wasn't anything new.
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What's changed, or at least what scientists are actively studying, is how often these
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patterns occur, how long they last, and what's influencing them.
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When the jet stream develops larger waves, those meridianal flowing north to south swings
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we talked about, it can create pathways for colder air to move much farther south than
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usual.
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Instead of staying tightly wrapped around the pole, parts of that cold air can spill outward
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along those dips in the flow.
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Then you get the headlines, that Arctic Blast, that Polar Vortex Outbreak, that Record
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Cold in the Southern US.
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When that cold air dips south in some areas, it then provides a pathway for a warmer air
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from the south to ride up the trough of the jet stream.
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So then you can end up in a situation where part of the country is dealing with extreme
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cold, while others experiencing unusually mild conditions.
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For example Florida may be dealing with freezing temperatures while parts of Oregon and Washington
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are seeing warmer than average temperatures that trigger early plant growth.
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There's also research looking at how the warming Arctic can affect the air mass across
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North America as a whole.
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Now, it's tempting to think of this in simple terms.
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Cold air is dense and warm air rises, but the reality is a lot more complex.
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What really matters here is the temperature difference between the Arctic and the regions
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to the south, that gradient.
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That contrast helps organize the structure of the atmosphere, including both the jet stream
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and the polar vortex.
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As the Arctic warms faster than the rest of the planet, the contrast changes, and when
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that happens, scientists are studying how it may affect the stability of our large-scale
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circulation patterns.
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One way to picture it is like a spinning top.
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When conditions are stable, the top spins smoothly in place, but if forces around it start
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to shift, even slightly, the spin can become less steady.
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It can wobble, it may stretch, and may drift from where it normally sits.
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That's similar to what scientists observe during certain effects, where the polar vortex
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becomes disrupted or displaced.
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When that happens, the cold Arctic air can go down into Florida, or Texas, or Mississippi,
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in places that aren't built to handle it.
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This is a topic scientists are still researching.
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Researchers are studying how these disruptions occur, what drives them, and how they may
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change in a warming climate.
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So when we connect this back to everything we've talked about, the jet stream, the
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waviness, the persistence, we start to see a bigger picture.
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Everything is connected, they're all part of the same atmospheric system.
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And small changes in that system, due to climate change, can show up as very real differences
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in the weather we're experiencing on the ground.
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The jet stream can be thought of as the steering system for our planet's weather, but what
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we're learning is the system doesn't always behave the way we expect it to, especially
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on a warming planet.
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The patterns that used to move through quickly, sometimes slow down.
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The boundaries that used to feel stable start to bend.
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And when that happens, weather changes.
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Heat waves stick around longer than they used to, rain continues and doesn't move on.
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A cold snap reaches farther than you might expect.
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We are seeing the atmosphere changing, and it's forcing us to rethink what we consider
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normal.
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Science tells us how the system works, but what we're seeing now is what happens when
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that system starts to shift.
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And those changes don't just affect the forecast, they affect how we live and how the world
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around us responds.
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I'm Dr. Mac, and this has been the Climate Translation.
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If you have a question about the climate you've been too afraid to ask, or if you have
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a differing opinion, I want to hear from you.
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I can use your viewpoints in future episodes.
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You can reach me at theclimatetranslation at gmail.com.
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I'll see you next time.