Not in recent memory have we had temperatures drop to as low as they have for the length of time that they've gone. It's been over a week since this unprecedented cold front, and it looks like it might go on for just a while longer. Over in the continental US, temperatures have gone below zero, even in usually warm Florida. For us here, it's been gloom and sweaters, with the occasional touch of rain.
What happened and how? Meteorologists are pointing to the collapse of the Arctic polar vortex due to sudden stratospheric warming (SSW). A polar vortex is a persistent, large-scale cyclone located at the earth's geographic poles. These gigantic storms form between the troposphere and the stratosphere, roughly between 15km and 60km above the earth. Typically they keep all the cold winds locked up at the poles. A sudden stratospheric warming is an event when the polar vortex slows down or changes direction.
This present SSW was caused by a major event owing to an extended increase of polar stratospheric temperatures. Although SSWs are a well-known phenomenon and occur with some frequency, the SSW we are experiencing now has caused the polar vortex to disperse over a wider area. Whereas the polar vortex typically forms around one or two cores, the polar vortex now has spread out into several cores, with a much wider reach.
Ironically at first glance, this event may be tied to global warming. Scientists believe that the continued loss of the Arctic ice pack is what is driving this collapse of the polar vortex. The loss of sea ice is leading to warmer oceans. What keeps the polar vortex strong is the difference between in temperatures between the Arctic surface and the upper atmosphere. With a warmer Arctic, the difference drops, leading to a much weaker and more spread out polar vortex, and, consequently releasing all that cold wind.
What does this all mean for us? It's somewhat reminiscent of the 2004 movie, "The Day After Tomorrow", which seemed pretty far-fetched at the time. Weather is a complex thing, and much more so climate. We don't know if this will go on or swing back. But the climate is changing, and the weather along with it, and now might be a good time to start planning for contingencies.