copied from an article from t.v. station ROCHESTER, N.Y. (WROC) — Every winter a new hype word is christened for winter weather. We all remember the ‘polar vortex’. This year, it’s ‘sudden stratospheric warming’, which believe it or not, has a close relation to the polar vortex.

There is a lot of complicated science behind how this works. We know for some of you the who, what, when, where, and especially the why is why you clicked on this. We recommend you start at the top and work your way down. For those who are less interested in the hard science behind it and more interested in how and if this could to affect you, jump down to the last section in the article where we bring it all together.


Most of what the News 8 Weather Team handles happens in the troposphere, or the lowest level of Earth’s atmosphere. This is the layer in which most, if not all, the weather that impacts us happens. Stretching from the surface to approximately 6-10 miles above our head, it’s the only layer of the atmosphere many of us, outside of the billionaires and astronauts, will ever exist in.

Above the troposphere lies the stratosphere. This is the second of a total of five layers in the atmosphere. The others being in order, the mesosphere, the thermosphere, and the exosphere after that it’s just space.

Every year above the arctic in the stratosphere, cold air, as cold as or colder than -75°F, pools into a mass of air that is contained by a strong band of winds that move west to east not unlike the jet stream that occurs in the troposphere. This mass of cold air and associated jet is called the ‘stratospheric polar vortex’ and is often centered over the north pole. This is not to be confused with the ‘tropospheric polar vortex’ which is just a build up of cold air near earth’s surface normally found trapped up in the arctic that occasionally spills south as a result of the stratospheric polar vortex.

Sudden Stratospheric Warming

There are a lot of ways this type of event can occur. Most focus on a weakening or even reversal of the direction from west to east, to east to west, of the stratospheric polar jet. We’ll discuss two ways this can happen which are both connected to a point. We’ll start with massive ‘waves’ that form in the troposphere that can bump along the bottom of the stratosphere and disrupt the stratospheric polar vortexes delicate balance.

Wave-induced sudden stratospheric warming

It takes a lot to disrupt the stratospheric polar vortex. To do it you need an exceptionally strong wave to form in the troposphere. These waves are often called Rossby Waves after the scientist whose research “discovered” them, or planetary waves due to their massive scale. The waves are also the same as the troughs and ridges you often hear us speak about when talking about our local weather.

These massive, planet spanning waves act much like a wave on the ocean does. When they crest they’ll often peak, and then spill out. The vertical motion of the peak can sometimes be enough to push air from the troposphere vertically into the stratosphere, as well as horizontally from south to north from the mid-latitudes towards the arctic disrupting the stratospheric polar vortex.

Both of these events contribute to a sudden stratospheric warming event. The horizontal south to north movement of air injects “warm” air into the into the mass of cold air which warms it. The other piece, the vertical motion of the wave, pushes air up into the stratosphere. Remember, what goes up must come down. When the air does come back down, it compresses and warms furthering the rapid warming. An example from NASA can be seen below of a stretching and separation type event, one of two types that can occur as mentioned above.

Northern hemisphere total ozone, potential vorticity on the 460 K potential temperature surface, and temperature on the 50 hPa pressure surface for 13 and 20 February 1989. This day is an example of a sudden stratospheric warming. (VIA: NASA)

Weakening of the stratospheric polar vortex

The stratospheric, and tropospheric polar vortexes, (remember they’re two different things), originate due to the Earth’s tilt. When the sun sets on the arctic circle for the last time each year, areas north of 66.5°N is plunged into darkness. Without solar radiation the region is plunged into unimaginable cold. Over time the cold air builds up around the arctic circle and as the contrast in temperature grows from south to north eventually the polar jet grows in strength around both separate polar vortexes.

The polar vortex is in the polar stratosphere, above the layer of the atmosphere (the troposphere) where most weather, including the jet stream, occurs. NOAA Climate.gov graphic.

From here on out we’ll return to our focus on just the stratospheric polar vortex to avoid too much confusion.

Eventually, as the season of darkness progresses, the sun does slowly return to the arctic circle. This causes the stratospheric polar jet, which contains the cold air, to weaken as the contrast between the “cold” and “warm” air weakens.

At this point, we start to see some crossover between these two different triggers for sudden stratospheric warming.

A strong stratospheric polar vortex, with a strong stratospheric polar jet, can often fight off most of the tropospheric waves that push into its domain. But as it weakens with the increasing sunlight in the arctic circle, it becomes more and more susceptible to being disrupted and collapsing in on itself. Sometimes this “collapse” might just happen on its own after enough warming from increasing solar radiation happens, but more often than not it will be taken out by repeated bumps from below before this happens. From here the process is relatively similar to before, but unlike in the previous scenario the stratospheric polar vortex wouldn’t have a chance to reform.

That’s great, but what does it mean for us?

The basic idea is that when the stratospheric polar vortex is strong, generally in the troposphere the jet stream is usually further north and stronger. This keeps much of the cold air trapped up north, regardless of where you are.

When the stratospheric polar vortex is weaker, or undergoing a sudden stratospheric warming event, sinking air from the stratosphere warms as it enters the upper troposphere where the jet stream is. When this area warms, it causes the jet stream to break down, allowing it to become more wavy and form the troughs and ridges you often hear us talk about on air. The troughs, or dips in the jet stream, are what allow the cold air to spill south.

In this case you can think of the jet stream like a dam. It holds back all the cold air like a dam holds back water. As the dam weakens, or the area around the jet stream warms, it weakens and eventually what’s being held back spills out.

Keep in mind though, there are a few things to know when talking about how a sudden stratospheric warming event influences our weather here at the surface. The time scale can be much longer than you think for one thing. From the onset of a sudden stratospheric warming event it can take anywhere from a few days to in some extreme cases up to two months for the impacts to be felt at the surface. Furthermore, these are relatively rare events on a yearly time scale. We often only see a sudden stratospheric warming event every other year.

The other important part is that it doesn’t guarantee an outbreak of cold air for your location. Where the jet stream ultimately dips, or where the break in the dam forms, isn’t going to happen in the same place every time. Sometimes it’s just being in the right spot at the right time.