Talk:Atmospheric circulation/Ferrel cell critique
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In the atmospheric circulation article, as in almost all textbook illustrations (with the exception of Laing, Fig. 145, p. 370 and Fig. 14.7, p. 373), a Ferrel cell is shown turning between equatorial Hadley cells and Polar cells as would a cog if all were such. Ferrel, after whom the cell is named, drew no such picture. He 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. In general, the surface flow of the Westerlies over the U.S. is a good example of statistics as a “Lie and More Lies.” In the Temperate latitudes, ground winds are of cyclonic, and anticyclonic, systems which have durations of a few days. In the Northern Hemisphere, the high pressure centers of the anticyclones tend to move slowly southeast and the low pressure centers of the cyclones 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). In other words, a sailor trying to use the Westerlies to sail east across the Pond, will be sorely disappointed and to make headway had better know the art of tacking in what will be mostly contrary winds. 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, named after Coriolis, who never published anything about wind systems, 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. These streams are a ragged lot as the front between cold arctic air and warm subtropical air is a ragged one. 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.
In short, the Ferrel cell does not exist. Air that flows north moves aloft along the Polar front swirls east and settles at the poles to move south and make its way as an unsteady ground flow back to the tropics.
The U.S. Air force at the end of the Second World War had bombers built to fly higher than the Japanese Zero’s operational height (above which the plane stalls). Plans were greatly compromised when these high flying fortresses encountered aloft jet streams that brought their ground speed, when they attempted to fly west to Japan, to near zero. The embarrassment may have been avoided if the design-engineers had not been schooled in the existence of the Ferrel cell. In such a system, no jet streams are possible. This is so, as the south flow of air at the top of the supposed Ferrel cell would veer to the right to meet the north flow of air that veers to the right at the top of the Hadley cell. The two opposed flows would cancel and there would be no subtropical jet stream. So anyone who bothered to think about the three dimensional flow pattern of the air would not have anticipated the existence of jet streams. Unfortunately, the lack of thinking things through has allowed the Ferrel cell, which does not exist in reality, to have iconic status in illustrations of global wind systems.
[edit] Reference
- Laing, David (1991). The Earth System: An Introduction to Earth Science Wm. C. Brown ISBN 0-697-07952-X
