Importance of the Polar Vortex

Good afternoon

Most of the time on sundays I find myself wanting to research or write about a related aspect of the current pattern and today is no different.


Since there is a buzz going around about a possible stratospheric warming event I thought i would write about the relationship between the Arctic Oscillation...North Atlantic Oscillation and the Polar Vortex. These features are very important regarding sudden stratospheric warming and the Polar Vortex is the engine that drives NAO/AO. The polar vortex and the AO/NAO are directly related to each other and a general rule of thumb is a strong Polar Vortex equals a positive AO/NAO and a weak Polar Vortex equals a negative AO/NAO. A negative Arctic Oscillation (weakPV) generally means colder temperatures in the eastern United States during Boreal winter and a Positive Arctic Oscillation (Strong PV) generally means warmer temperatures in the eastern United States during boreal winter.

A strong Polar Vortex tends to be more concentated near the pole and circular in shape... it will generally keep the cold air bottled up near the polar regions (as seen in the past 60 days)... but a weaker Polar Vortex will become less concentrated near the polar regions and will become elongated and may even split into several smaller vorticies (as seen in the current pattern)...these smaller vorticies tend to move away fron the polar region and this allows higher pressures to settle in near the polar and arctic regions (yet to be seen). As higher pressures take hold near the pole... lower pressures and Arctic air are transported southward via the smaller vorticies that once were a strong polar vortex.

Strong Polar Vortex
 
Weak Polar Vortex




There is also a direct relationship between the AO and the NAO due to the NAO being measured in close vicinity to the Arctic region. When stratospheric warming occurs lower pressures are generally replaced with higher pressures in the Arctic regions. This usually means some type of blocking occurs in the high lattitudes of the NAO region due to these higher pressures. When this blocking pattern occurs the colder temperatures of the Arctic are forced southward into the eastern United States by a buckle in the jet stream caused by this blocking pattern that is the negative NAO/AO.


To illustrate just how related the NAO and AO are.. here is a graph showing the fall readings of the AO and NAO indicies. Notice how they behave in a very similar fashion to each other




Hopefully this little writeup will help somebody get a better understanding of how the Polar Vortex is the most important feature regarding a cold and snowy pattern here in the eastern United States. I have been watching this feature becoming weaker and displaced here on our side of the globe lately... this and the recent changes in modeling of the AO indice is a VERY good sign that the NAO/AO could be headed to a more conducive value for us winter wx lovers this season... only time will tell.