Animations of the Stratospheric Polar Vortices
The stratospheric polar vortices are features of the winter hemisphere that span from about 10 km to 50 km above the surface. They are highly variable features of the atmospheric circulation: some years they grow in to extremely strong vortices that isolate the air within them from the mid-latitudes; other years they are disturbed by Rossby waves with lengthscales comparable to the radius of the planet.
The detailed evolution is well-captured by modern reanalysis products like ERA 5.
They can be visualized in terms of a quantity called `potential vorticity:' the polar vortex corresponds to regions of high potential vorticity (positive in the Northern Hemisphere, negative in the Southern Hemisphere). Potential vorticity is roughly conserved following the flow of the atmosphere (meaning that a parcel of air will retain the value of potential vorticity it has as it moves around), and air in the atmosphere roughly follows quasi-horizontal surfaces called isentropes. Animating potential vorticity on isentropic surfaces provides beautiful illustrations of atmospheric flow in the high-latitude stratosphere.
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Stratospheric Sudden Warming 2018
The Arctic vortex was strongly disrupted in February of 2018; this event has been linked to a range of surface extremes, including the `Beast from the East', a major cold-air outbreak over much of Europe, and the arrival of rain that ended a severe drought on the Iberian Peninsula.
The slight 'jumps' every 12 hours in the animation are a result of the data asimilation cycle used by ERA 5 to tie the forecast evolution to observations.
While the Antarctic vortex is less dramatically variable than the Arctic vortex, one can also see the effects of wave breaking at the vortex edge that constantly draws filaments of higher potential vorticity air into the mid-latitude 'surf-zone'. The ozone hole coincides with the vortex itself.
Another well-studied event, the Arctic vortex split dramatically in late January 2009. This was an extended recovery event (or 'Polar-night Jet Oscillation' event; see Hitchcock et al. 2013) characterized by the complete erosion of high potential vorticity air after the split. When this occurs it takes several months for the vortex to re-establish itself.
Although early-winter variability in the vortex tends to get less attention as it is less dramatic in a relative sense, the vortex can still be quite dynamically active. In the early parts of the 2016-2017 winter the vortex was perturbed by both wave two and wave one anomalies.