Earth’s atmospheric circulation distributes heat from the equator to the poles through three convection cells in each hemisphere. The rotation of the Earth, surface features, and ocean currents influence global atmospheric patterns. The Coriolis force causes winds to curve and produces rotational winds around high and low pressure cells. Seasonal changes and variations in land and ocean areas also affect atmospheric circulation. Accurate computer models have helped scientists understand climate and weather patterns and predict future changes.
Atmospheric circulation is the global movement of air, which distributes the heat received from solar radiation from hotter regions to colder ones. If the Earth did not rotate on its axis and had a smooth, even surface, warm air would rise at the equator and flow towards the poles. There it would cool and sink, creating a flow back to the equator along the surface of the Earth. There would be two large, uniformly rotating convection cells, one in the northern and one in the southern hemisphere. Instead of this simplified scheme, Earth’s atmospheric circulation is much more complex.
An oversimplified model of the Earth’s atmospheric models has one large convection cell in each hemisphere. In reality, there are three convection cells in each hemisphere. Warm, humid tropical air near the equator rises and flows off the equator forming the Hadley cell. Above the poles, cool, dry air descends, driving the Polar Cells. Ferrel cells are more variable and are found between Hadley and polar cells.
The rotation of the Earth, the tilt of its axis, surface features, ocean currents and local weather patterns all influence global atmospheric patterns. Instead of winds flowing in straight lines, the Earth’s rotation causes them to curve. The Coriolis force diverts the northern hemisphere winds to the right and the southern hemisphere winds to the left. It contributes to the formation of westerly winds in mid-latitudes and easterly winds in the tropics and polar areas. The Coriolis force also produces the rotational winds around the high and low pressure cells.
Seasonal changes in atmospheric circulation are caused by the tilt of the Earth’s axis. As the sun’s direct rays move north and south of the equator seasonally, circulation patterns change. Features on the Earth’s surface also affect global atmospheric circulation. A larger land area in the Northern Hemisphere and the corresponding larger ocean area in the Southern Hemisphere cause variations in the three convection cells in each hemisphere.
The many complex factors that influence atmospheric circulation have made it difficult for humans to adequately model global air circulation patterns. Only in the 20th century were accurate models of atmospheric circulation produced using computers and satellite data. These models closely resembled how the atmosphere actually worked, helping scientists better understand climate and weather patterns. Early advances in weather forecasting using computer modeling evolved as much more realistic and complex models allowed for more accurate forecasts. Atmospheric circulation models are used to understand long-term climate changes in the past and predict the effects of changes in the future.
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