The global circulation of air currents is the result of the Earth’s temperature differences that create air pressure changes. The prevailing air currents happen when air flows from a high pressure zone to a low pressure zone. These currents, which also affect the flow of ocean currents, influence both our local weather and global climate.
Most of the movements of air currents on a global scale happen in the Earth’s upper atmosphere. As the sun-warmed air rises, it diverges in the troposphere and moves toward the Earth’s poles in several giant loops called circulation cells. If this atmospheric movement did not happen, the poles would grow colder and the equator would grow hotter.
One of the driving forces of global air currents is the uneven heating of the Earth’s surface. The atmosphere is heated much greater and faster at the equator than at the poles. Hot air rises and cold air sinks, so air currents form when the atmosphere moves excess hot air from the warmer low latitudes to cooler high latitudes, and cool air rushes in to replace it.
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The equator receives the sun's direct rays and the air is heated and rises, creating a low pressure zone. Thirty degrees north and south of the equator, this warm air cools and sinks and moves back to the equator's high pressure zone while the rest of the warm air flows toward the poles. When air flows from high pressure to low pressure, the strength and proximity of the two pressure areas are known as the "pressure gradient.” The closer these pressure areas are, the stronger the pressure gradient, producing stronger air currents.
The Earth's rotation on its axis prevents air currents from flowing directly north and south from the equator. Instead, these air currents are deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, a phenomenon called the Coriolis Effect. With this rotation, three air circulation cells between the equator and the poles are created that keep the warm and cold air currents circulating in loops that feed each other. Meteorologists identify these as the Hadley Cell between the equator and latitude 30 degrees, the Ferrel Cell between latitudes 30 and 60, and the polar cell between latitudes 60 and 90.
When warm air masses in the south abruptly meet cool air masses from the north, the high air pressure gradients create very high wind speeds known as the jet stream, a narrow band of air that flows from west to east around the Earth at speeds reaching 200 miles per hour. Although the jet stream typically flows at 20,000 feet or more, the high wind speeds can still influence weather patterns on the surface.