Wind is mainly the result of thermodynamic principles and the Coriolis effect, due to the Earth’s counterclockwise rotation. Warm air around the equator is lifted, which creates a suction effect for air masses coming from higher (or lower) latitudes. The high-altitude air mass moves either north or south until its temperature is low enough for it to “sink” and start to converge toward the equator. As these air masses move, the Coriolis effect shifts their direction. The outcome is a system of circulation known as a “cell”; three of which are between the equator and the North Pole and three others towards the South Pole. The most significant is the Hadley Cell, from which the “Trade Winds” result.
Global wind patterns have both a historical and contemporary significance for transportation. Historically, wind patterns were linked with the trade routes of sailships. For instance, a relatively stable wind pattern over the North Atlantic enabled ships to set sail from Europe using the dominant westbound wind on the southern part of the North Atlantic and return using the dominant eastbound wind on the northern part of the North Atlantic. A similar pattern exists over the North Pacific. The monsoon over the Indian Ocean has also been linked to maritime trade in the past, as ships sailed from the Middle East to Asia in winter and undertook the westbound voyage back in summer when the dominant wind direction shifted. With the progressive abandonment of commercial sailing in the 19th century, wind patterns have stopped playing a significant role in maritime transportation. Intercontinental maritime shipping now follows the great circle distance, regardless of wind direction.
The growing importance of air transportation is constrained by wind direction, particularly for long-distance hauls. Eastbound crossings over the North Atlantic and the North Pacific are shorter than westbound crossings because of the cumulative wind effect. For instance, a flight between New York and London is scheduled to last about 7 hours (from gate to gate) eastbound and about 7 hours and 45 minutes westbound. The scheduled difference of 45 minutes is the outcome of dominant winds. Thus, the westbound transatlantic flight consumes more energy than the eastbound flight.