Ferrel cell

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Main article: Atmospheric circulation

The Ferrel cell is usually shown between the Hadley and Polar cells, e.g. atmospheric circulation. It is named after William Ferrel, who was concerned with describing the surface flow in the Temperate zone of air that came from the Horse Latitudes, namely the Westerlies. In the region of the Atlantic ocean the Westerlies are the northern part of the general circulation of air about the high pressure system that sits over the Horse latitudes. The main 'problem' with the Ferrel cell is that it is thermally indirect.

However, the true atmospheric circulation is rather more complex than the simplified zonal mean pictures would lead one to suspect... It is possible to argue that the Ferrel cell does not exist.

[edit] North American westerlies

In general, the surface flow of the Westerlies over the U.S. does not follow the expected flow. In the Temperate latitudes, ground winds are of cyclonic, and anticyclonic, systems which typically have durations of a few days. In the Northern Hemisphere, the high pressure centers of the polar anticyclones are encouraged southward along the east side of the Rocky Mountains, and tend to move slowly southeast. The low pressure centers of the cyclones, particularly from the warm southern waters, move slowly northeast. Their average, and slow as to be imperceptible, westerly component of motion is, as a practical experience, overwhelmed by their strongly felt veering component (the vectors of which statistically add to zero). The resulting flow has no constant direction and is different from that expected over open ocean.

[edit] Jet streams

In the zone of the Westerlies, pressure-driven warm ground-air flowing north is forced to rise over pressure-driven cold ground-air flowing south. The Coriolis effect, causes the north moving air, which is forced to rise at cold and warm fronts, to veer to the right and form westerly jet streams aloft. The flow of air aloft is not acted on by any pressure that could cause it to flow back to the subtropics. But as friction slows its motion, the air aloft above the Polar front can move north to become the downward settling frigid air of the Polar zone. From there it flows outward over the ground as the Polar easterlies.