What the Polar Vortex Will Do to Earth this Decade

When I started my Milankovitch cycles  video with a reference to Game of Thrones, I didn’t realise exactly how apt my analogy  was. In that TV show, the armies of the Night King in the north are trapped behind a giant  wall. Just like in the TV show, it turns out that on Earth there exists a powerful, icy  force to the North that is seeking to overflow its bounds and rush southward.

That powerful  winter is also kept at bay by a mighty wall, one that allows the nations to the South  to enjoy relatively tranquil conditions. And just like in the TV-show, that wall  eventually gets breached, in a wave of ice that sweeps down and threatens the lives of all  those in its way. You might not recognise what I’m talking about.

Where is this wall? And  what is the icy winter it protects us from? The answer to the first question is a name that I  find particularly cool; the Polar Night Jet.

And it turns out that the Polar Vortex it protects us  from is a biting chill not to be underestimated. What is the Polar Vortex? And how does the Polar  Night Jet protect us from it?

I’m Alex McColgan, and you’re watching Astrum. And today we’ll learn  more about this climate-shattering phenomenon, and what happens whenever the Polar Night Jet  breaks down and the polar vortex is unleashed. There are actually two polar vortexes: one  at each pole of the planet.

And even there, each vortex comes in two parts: a tropospheric  polar vortex, spinning in the section of the atmosphere known as the troposphere, from ground  level up to about 10 or 15 km. This is where 75% of the total mass of the atmosphere resides.  Above that lies the stratospheric polar vortex, a technically separate weather phenomenon  that has its own size, seasonal cycle, and influence on the global climate.

Each of  these massive cyclones sits over the pole, spinning with the planet’s rotation, with  wind speeds that can reach up to 240 km/h. Why do these winds happen? The first piece  of the puzzle is temperature difference.

At locations like the equator where sunlight is  most concentrated, the air is warmed and starts to rise. As it does so it creates an area of low  pressure beneath it that draws air into it from its surroundings like a giant vacuum cleaner.  Meanwhile, at places like the poles where it’s much colder, air contracts and falls, creating  zones of high pressure where air molecules want to spread out like a crowd of school children being  released into an open field.

So naturally, with these two forces at play, there is a tendency for  air to rush from the poles towards the equator. Freezing cold winds are constantly trying  to escape from the North and South Poles. This model is a little simplified, though,  as wind does not travel in one continuous line from the pole to the equator.

Instead,  because air from the equator cools and falls much sooner than the pole (at around latitude  30°), and air from the poles warms and rises much sooner than the equator (at latitude 60°),  there are 3 cells of air on each hemisphere that air circulates in. The Polar cells (the air  masses above the poles) and the Hadley cells (the air masses above the equator) both cycle  in the temperature-driven way I described. However, the middle cell – known as the Ferrel  cell – is not temperature driven.

Like a gear, it is dragged by the rotation of the other two  cells and rotates opposite to their motion. In terms of our northern polar vortex, this means  that once the air from the pole heads south, it’s met by warmer wind travelling in the opposite  direction. And when two air fronts of different temperatures meet, they clash rather than  mix.

So, the Polar vortex is trapped, bounded, clashing against winds coming in from all sides.  There’s more at play here, though. If this was on its own, the cold air from the North could just  slide underneath the warm air from the south, not really being trapped at all.

There is a second  force at play that redirects those winds, spinning them up into a vortex that keeps them circling the  poles rather than coming down towards the equator. Where does the spin come from? It’s due  to something known as the Coriolis force.

In a simple, flat world, cold wind from the  poles would travel towards the equator, while warm wind from the equator would float over it  towards the poles. But the world isn’t a simple, flat sheet – it’s a rotating sphere. You are  travelling right now at somewhere between 0 km/h if you’re at a pole (and decided to watch an  Astrum video while you were there ), and 1600km/h at the equator, from the west to the east.

You  might not notice this fact because everything next to you is on average travelling at  the same speed, in the same direction. But what happens if you were to travel  from the equator towards the pole? Conservation of momentum states that you  would still be travelling eastward at the same speed as previously, but suddenly the Earth  beneath you is not travelling quite so fast.

Remember, at the pole, you’d have 0 eastward  speed, but would simply be rotated slowly. If you keep all your eastward momentum from  the equator and travel towards the pole, suddenly it will appear compared to everything  else like you are travelling east really fast. In practice, this means that air that travels up  towards a pole from the equator (whether towards the north pole or the south) will not go straight  up, but over large distances will start to curve towards the east.

This rapidly eastward-travelling  air is why you get jet streams. There are at least 4 of these, straddling the gaps between the Hadley  cells, the Ferrel cells and the Polar cells. The Subtropical Jet stream lies between the first two,  and is a little weaker, but the jet streams we are interested in are the polar jet streams, ringing  the frigid air off that develops in the North and South poles.

These ribbons of air circle the globe  in an almost continuous path, a little underneath the boundary between the troposphere and the  stratosphere. They are only a few kilometres deep, but can be hundreds of kilometres wide, and in  their hearts, the wind can travel at 400 km/h. As a reminder, over 120 km/h is getting  into strength level of hurricanes.

The jet stream around the south pole  is fairly stable. Its powerful winds overrule the polar winds trying to leave  the polar air mass, whipping them along with it and dragging the entire polar cell  into a massive, antarctica-spanning vortex. At this point a keen-eyed observer might have  noticed a flaw in this model.

If conservation of momentum means that air going from the equator  towards the pole veers towards the east, why is it that air travelling from the pole towards  the equator doesn’t do the exact opposite? It has zero momentum, moving to zones that have  considerably more momentum – comparatively, it should be quickly left behind, appearing to  start spinning to the west. This is true, but cold wind has much more friction to contend with  as it starts to slide underneath the warm front, and then drags along the ground.

This seems  to slow it down enough that the countervailing jet stream overrules it. It’s important to note  this tension at play, though, as it becomes much more important in the Polar Night Jet. The Polar  Night Jet is the Jetstream that bounds the vortex at the North pole.

Specifically, it bounds the  stratospheric polar vortex, keeping it in check during the coldest part of the year for the North  – the polar night. Here during the winter months, the sun is absent from the sky entirely,  creating even more freezing temperatures. Interestingly, this colder climate creates a  deeper pressure difference between the air around the pole and the air further south, which actually  strengthens the forces that create the Polar Night Jet, meaning that during the coldest part of the  year, this freezing air is usually well contained.

However, this does not always hold true.  There are things that can disrupt a Jetstream. There are certain zones, such as the boundary  between sea and land, or the presence of a large mountain, that can cause disruption to wind. 

Coastal environments create their own winds that can suck in jetstreams, while mountains  force an air current to move around it. Even other weather phenomenon such as El  Nino, which you might recognise from one of my recent videos, can have an impact  on the path the Jetstream takes. As the Jetstream is not fixed down, but is a balancing  point between a range of opposing forces, hitting such obstacles causes it to deviate  from its course.

And once it starts deviating, it will rock back and forth like a string that  has begun bouncing. It shifts, no-longer is in balance, overcorrects itself, and is no longer  in balance again, and overcorrects itself again, in massive planetary waves that cause the polar  night jet to meander around the Earth, rather than travel in a straight line. And these oscillations  can reach a point where there is a breach.

The first sign of this comes in the  form of a Sudden Stratospheric Warming, most common in late winter. An SSW even can  represent a time where temperatures rise in the polar region by as much as 50°C over the  course of just a few days. Something within the system of the Jetstream can be so thrown  by this that it leads to the southern-moving westerly winds overpowering the Jetstream,  partially or completely reversing its flow.

No longer contained, arctic wind moves south and  meets warmer and warmer air, and pushes faster and faster south to attempt to balance the gradient.  The entire jet stream buckles, and suddenly, it pivots. It massively reorients itself,  travelling down the planet so that regions like Europe and America – usually safely on the warm,  temperate side of the polar night jet – suddenly find themselves in the domain of the polar  vortex.

The forces of winter have arrived. In fairness, not all of these events are  devastating. With sufficient preparation, you can simply put on some warm clothes, or try  to avoid going outside for the month or so that the polar winds are overhead.

As long as you’re  ready for cold, it’s not the end of the world. However, sometimes the outcome is serious. In  the UK in 2009-2010, the Big Freeze saw parts of Scotland reaching temperatures as low  as -22°C, the coldest in nearly 40 years, with widespread transport disruption,  event closures, and power failures.

Sadly, this in turn lead to the death of 25  people. In the US, the 2019 January-February north American Cold wave saw a polar vortex move down  across much of the country, with similar outcomes. Some areas saw temperatures as low as -50°C if you  also take into account windchill factor from the blustery, freezing winds.

Snow storms raged.  You could get frostbite from being outside in just 10 minutes. Sadly, another 22 people died,  with hundreds more needing frostbite treatment.

Responsible was the ranging polar vortex. In  time, the imbalances in the global temperatures restore themselves, and the jetstream returns  to its previous position. However, it’s worth noting that some level of Jetstream breakdown  occurs in the north 6 times every decade.

If you live in the Northern Hemisphere, you will  likely see many more of these events over the course of your lifetime, although hopefully  not all as powerful as those two examples. In the South, you are likely safer –  there have only ever been 2 instances in recorded history of the Southern Polar Jet  Stream breaking down in the same way as the Northern one. It has happened, though, and the  mechanisms behind it are not fully understood.

It’s difficult to say, as global temperatures  gradually rise, what influence this might have on the Jetstreams. Some evidence indicates that they  are travelling further poleward on average, year on year, although this is apparently not unheard  of in the planet’s history. There is some more evidence that the jetstreams have strengthened  since 2002.

If so, we should be grateful. Although unpleasant, the biting cold of the polar vortex  usually is only a passing weather phenomenon. We see it return north within a month.

But if the  Jetstream were to go, the polar vortex would come down from the North to stay, and we’d truly know  what it is like to live in arctic conditions. The more I’ve learned about the subject, the more  I’ve discovered that the winds of our planet are this fascinating weave of interplaying forces  and effects that tug and pull on each other, finding perfect balances and yet constantly  shifting in rhythms and patterns. And yet, it does so practically invisibly.

So much  is going on that we simply do not see, down here on the ground, just because air  is, well, air. And yet, I’ve learned its importance. The Polar Night Jet is not just wind  with a cool name.

It is a bastion of protection, a wall against the frozen wind. It really  makes you think of the incredible majesty of the world around us – how much is going on that  protects us, that we simply do not see. If you’ve enjoyed learning about the jet stream and  the polar vortex, don’t worry; there’s more to discover.

Jet streams as a phenomenon were  not always understood, and there’s an excellent article on them called “Searching for the River of  Wind” on the website of today’s sponsor, Nautilus. Nautilus is a fantastic science publication  that I’ve become really impressed with lately, for its accessibility, strong narrative sense, and  fascinating insights. Its award-winning authors are scientists from many different disciplines,  so you get cutting-edge research on all sorts of topics, including one near to the heart of any  Astrum viewer; Space!

Don’t just take my word for it, though – in a rare event, Nautilus is offering  a 15% discount on their yearly membership, so now’s the perfect time to go see for yourself.  Click on my link in the description below! Thanks for watching!

If you liked this video,  you’ll love these other videos on the various cycles of Earth. A big thanks to my patrons and  members. If you want your name added to this list, check the links below.

All the  best, and see you next time.