The circumpolar vortex is characterized by standing wave phenomenon of upper-air long waves (sometimes called called Rossby waves) consisting of three to six alternating ridges of high pressure ridges extending poleward and low pressure troughs extending equatorward radiating outward from the pole ( Fig. 1.1.4) This configuration of ridges and troughs is slow moving to relatively stationary over time for periods several weeks to months.
Most relevant to North America, are two troughs corresponding roughly with the Aleutian Low and the Islandic Low. Similarly interleaving ridges correspond roughly the Pacific High and the Bermuda High.
The polar front, from this more detailed view, has the form of loops separating the high and low pressure portions of the standing wave pattern.
The pattern of upper-air long waves is subject to periodic changes. Over a 3 to 8 week index cycle, the north-south amplitude of the trough-ridge protrusions grows to a point where small cells of low and high pressure budd off from the main vortex. These then dissipate and the whole process begins again ( Fig. 1.1.4) The polar front thus follows this cycle.
Cellular boundaries are associated with jet streams -- relatively confined, high velocity winds in the upper-air. The polar jet stream is associated with the polar front. The polar jet stream follows the movements of the circumpolar vortex (See above.) in the upper atmosphere and guides the position of the polar front at the surface. The subtropical jet stream is associated with the 30o cellular boundary.
