Polar Night Vortex

Scientists: Lorenzo Polvani, R. Saravanan
Animators: Mark Taylor, John Clyne, Dave Kennison

Abstract

In early winter, cold temperatures result in the formation of a strong circumpolar flow in the stratosphere, known as the Polar Night Vortex. This vortex produces favorable conditions for ozone depletion.

Description

The breakdown of the Stratospheric Polar Night Vortex is an atmospheric event that occurs once or twice each year in the polar wintertime stratosphere. As the polar vortex is formed, sharp gradients of potential vorticity at the vortex edge isolate polar air from the air at lower latitudes, producing conditions favorable for wintertime polar ozone depletion. Rossby waves propagating upward from the troposphere along the edge of the Polar Vortex grows exponentially in amplitude, eventually tearing the vortex apart.

This simulation of vortex breakdown has been computed at NCAR with SEAM, an spectral element atmospheric model, running on a 64 processor HP SPP2000, (Sioux). The computation required 2.5 days to compute 16 simulation days.

The imagery and animations below depict the flow of the Polar Vortex by visualizing Potential Vorticity (a variable that acts as a tracer) over the 16-day simulation. In the second and succeeding images, the height of the data has been greatly exaggerated to better show the rich vertical structure contained in the vortex. In reality, the vortex is only a few tens of kilometers thick - a pancake-thin region that can extend over much of the Northern Hemisphere.

Isosurfaces of Potential Vorticity

This image shows a satellite view of the earth from space with three isosurfaces of Potential Vorticity mapped over the Northern Hemisphere from day 16 of the simulation. Brighter colors correspond to increasing Potential Vorticity. The animations at right, show the entire 16-day evolution.

Isosurfaces of Potential Vorticity with Height Exaggerated

A stereographic projection of the Northern Hemisphere from day 16 of the simulation is seen above with the data field exaggerated 200 times in the vertical direction. The animations on the right show the mapping projection as it is warped from satellite view to orthographic, followed by the scaling of the vertical axis.

Volume Rendering of Potential Vorticity with Height Exaggerated

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This image depicts a volume rendering of the Polar Vortex. The vertical axis is exaggerated 200 times to better show the vertical structure of the vortex. The view is looking down from directly above the North Pole.

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