Atmospheric circulation
The smaller-scale weather systems – mid-latitude depressions, or tropical convective cells – occur chaotically, and long-range weather predictions of those cannot be made beyond ten days in practice, or a month in theory (see chaos theory and the butterfly effect).
The work produced by that engine causes the motion of the masses of air, and in that process it redistributes the energy absorbed by the Earth's surface near the tropics to the latitudes nearer the poles, and thence to space.
The large-scale atmospheric circulation "cells" shift polewards in warmer periods (for example, interglacials compared to glacials), but remain largely constant as they are, fundamentally, a property of the Earth's size, rotation rate, heating and atmospheric depth, all of which change little.
As the air moves poleward, it cools, becomes denser, and descends at about the 30th parallel, creating a high-pressure area.
[3] The poleward movement of the air in the upper part of the troposphere deviates toward the east, caused by the coriolis acceleration.
At the ground level, however, the movement of the air toward the equator in the lower troposphere deviates toward the west, producing a wind from the east.
[4] Part of the air rising at 60° latitude diverges at high altitude toward the poles and creates the polar cell.
The air of the Ferrel cell that descends at 30° latitude returns poleward at the ground level, and as it does so it deviates toward the east.
As the air at the surface moves toward the equator, it deviates westwards, again as a result of the Coriolis effect.
These ultra-long waves determine the path of the polar jet stream, which travels within the transitional zone between the tropopause and the Ferrel cell.
The sheer volume of energy that the Hadley cell transports, and the depth of the heat sink contained within the polar cell, ensures that transient weather phenomena not only have negligible effect on the systems as a whole, but — except under unusual circumstances — they do not form.
While the Hadley, Ferrel, and polar cells (whose axes are oriented along parallels or latitudes) are the major features of global heat transport, they do not act alone.
This entirely ocean-based cell comes about as the result of a marked difference in the surface temperatures of the western and eastern Pacific.
The process begins when strong convective activity over equatorial East Asia and subsiding cool air off South America's west coast create a wind pattern which pushes Pacific water westward and piles it up in the western Pacific.
While he was never successful in doing so, his work led him to the discovery of a link between the periodic pressure variations in the Indian Ocean, and those between the eastern and western Pacific, which he termed the "Southern Oscillation".
This and the corresponding effects of the Southern Oscillation result in long-term unseasonable temperatures and precipitation patterns in North and South America, Australia, and Southeast Africa, and the disruption of ocean currents.
Meanwhile, in the Atlantic, fast-blowing upper level Westerlies of the Hadley cell form, which would ordinarily be blocked by the Walker circulation and unable to reach such intensities.
These winds disrupt the tops of nascent hurricanes and greatly diminish the number which are able to reach full strength.
[13] El Niño and La Niña are opposite surface temperature anomalies of the Southern Pacific, which heavily influence the weather on a large scale.
In the La Niña case, the convective cell over the western Pacific strengthens inordinately, resulting in colder than normal winters in North America and a more robust cyclone season in South-East Asia and Eastern Australia.
There is also an increased upwelling of deep cold ocean waters and more intense uprising of surface air near South America, resulting in increasing numbers of drought occurrences, although fishermen reap benefits from the more nutrient-filled eastern Pacific waters.
