Saturday, January 19, 2013

Complete Polar Vortex Collapse Possible in Lower Stratosphere

It now appears that lower levels of the stratosphere could begin to see a collapse of the polar vortex, in a  forecast coming out just a day after I showed how the upper stratosphere had experienced its polar vortex collapse, as seen in this article. (By the way, the unit 550 K refers to the isentropic level, which equates to nearly ~90 millibars- one of the lowest levels of the stratosphere)

The phenomenon of the polar vortex collapse involves just what the name implies: collapse of the semi-permanent polar vortex. The polar vortex is the low pressure system that sits over the Arctic, regulating how much cold air escapes south into lower latitudes. When the vortex is weak, the grip on cold air is weaker, so the cold air escapes south (this is also known as a negative AO). When the vortex is strong, cold air is held up north especially strong, so warm air prevails in lower latitudes (a positive AO is described here).

The polar vortex can become so weak that it needs to split up into multiple vortices. When this happens, it's like you're holding paper on a windy day, but you release your grip on the papers. You only manage to retrieve a few. The cold air does a similar action in which the cold is released and flows to southern latitudes, but some cold still remains within the vortices. The cold isn't the only thing going to southern latitudes in this situation, though- when a split happens, the vortices tend to drift south to wherever the atmospheric pattern will allow them to go. Some recent forecasts have one vortice entering much of the United States, but that's a post for another time.

This forecast, also from the ECMWF and also for the Day 10 forecast, shows potential vorticity values for the 850 K level (~15 millibars). As you can see, there are no more oranges or whites or reds. Why is that? The polar vortex has disintegrated. I kid you not, this is the classic example of the polar vortex completely demolished. There is no polar vortex at this level. If this was in the lower stratosphere, one could only imagine what cold would be unleashed upon the Earth in such a situation.

I have been seeing increasingly-weak forecasts for potential vorticity values in the lower levels of the stratosphere, telling me this could be a sign that a collapse of the polar vortex is impending. A certain, trustworthy indicator tells me cold will be in the vicinity, the question is where does it manage to penetrate into the US.

Andrew

8 comments:

Simon said...

Nice post Andrew. If it completely disintegrates, how does it manage to start up again, and how long might it take?

Anonymous said...

I don't think the PV is disintegrated because oranges and whites aren't on the color legend but correct me if i am wrong andrew.

Andrew said...

Simon: It would take a long time to get back going, if it ever were to for the rest of winter.

Andrew said...

Anonymous at 3:30: The lack of oranges and whites means there is no polar vortex.

Tim Johnson said...

The GFS model is way different. It shows the vortex staying near Alaska. Do you see the vortex over Alaska or will be in the U.S or will it be completely gone?

Anonymous said...

Andrew how would you go about creating a seven day forecast for the Chicago area? I'm an aspiring met:)

Andrew said...

Anonymous at 5:28: You just look at the models for precipitation, temperatures and winds. I can't really describe it, it's more of a learning thing than a Q and A

Andrew said...

Tim: I have not had time to study the Alaska portion at this time.