ORLANDO, Fla. – Polar vortex. Sudden stratospheric warming.
The winter buzz words are back. But what do they mean?
Here’s the deal. You may hear polar vortex and sudden stratospheric warming thrown around a bunch during the cool months. They are scientific and meteorological things, however, they are often talked about incorrectly and used to hype things up.
So what are they?
A sudden stratospheric warming event is just that; a sudden warming of the stratosphere miles above our heads.
This event disrupts the stratospheric polar vortex, weakening it significantly. As a result, cold, polar air at the surface can plunge through the U.S. including into Florida.
What is the polar vortex?
This is where it gets a little complicated.
The polar vortex is always there. It sits high above the surface, about 10-30 miles, in the stratosphere over both the north and South Pole.
We’ll focus on the North Pole since that’s what can indirectly impact us.
This feature is most prominent during the cold months in the northern hemisphere.
When the vortex is strong or stable, the cold remains tightly-packed closer to the poles with warmth expanding in the south.
During a sudden stratospheric warming event, the polar vortex in the stratosphere weakens, sometimes enough to reverse the westerly winds that spin around it.
This can start the process of Arctic air spilling into the Deep South.
This, however, is not the polar vortex that impacts our weather directly.
Wait, there’s another one?
There is also a polar vortex in the troposphere, the layer of the atmosphere where humans live.
This polar vortex can also weaken after a sudden stratospheric warming events as the weakness in the stratosphere propagates downward.
This typically happens a couple of weeks after the warming in the stratosphere takes place.
This weakness or displacement of the tropospheric polar vortex often leads to the jet stream becoming very wavy. A wavy jet stream leads to the potential of cold air outbreaks and storms.
Sometimes these significant cold air outbreaks reach the Sunshine State.
The tropospheric poler vortex is measured by the Arctic Oscillation.
When the AO is positive the vortex is strong and the cold air remains locked in at the poles.
When the AO is negative the vortex is weak leading to the wavy jet stream.
The overall weather pattern tends to be cold and stormy when Arctic Oscillation is in its negative phase and the tropospheric polar vortex is weak.
It’s important to note that impacts at the surface do not always occur after a sudden stratospheric warming event.
Significant sudden stratospheric warming events occur every 1-3 years.