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Definition:
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The term polar vortex is used to describe several different features in the atmosphere. It most commonly refers to a planetary-scale mid- to high-latitude circumpolar circulation. There are distinct tropospheric and stratospheric circumpolar vortices. The tropospheric polar vortex is usually defined by geopotential contours that lie within the core of the tropospheric westerlies.1 The tropospheric vortex edge is generally between 40˚ and 50˚ latitude (Fig. 1), and the vortex exists throughout the year but is strongest during winter when the air within the polar vortex is the coldest. The term 'polar vortex' is sometimes used in reference to smaller-scale (meso- to synoptic scale) vortices that usually occur within the tropospheric polar vortex in polar regions near the tropopause - for example, tropopause polar vortices. 2. The stratospheric polar vortex exists from spring to fall and usually extends from just above tropopause to the upper stratosphere (see Fig. 1). The stratospheric vortex generally increases in size from the lower stratosphere to the upper stratosphere where its edge is located around 50˚ latitude. The stratospheric vortex breaks down, and the circumpolar flow reverses, during summer. 3. Circumpolar vortices have also been observed on other planetary bodies (e.g., Mars, Venus, Saturn, and Titan). 4.
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