Global Air Circulation Patterns We

Global Air Circulation Patterns

We know so little about the place that has been our home for thousands of years. There are so many unseen functions of the planet Earth that have such strong influences on all aspects of the creatures which walk upon it. The forces of the air and atmosphere are some of the most influential on global weather patterns. Understanding the atmospheric conditions of the Earth gives us a glimpse into our own home which was previous unseen. These conditions rule our everyday lives, yet go largely unnoticed or completely understood by most of humanity. The weather patterns we are so vulnerable to come from the interaction of three general zones, the Hadley, Polar, and Ferrel Cells, which consistently move and maneuver earth around the globe. Their interaction with each other affects the climate as well as individual weather patterns. Although they have been present since our existence on the Earth, these atmospheric conditions are not permanent. As they fluctuate annually, they are also threatened by human forces that have negatively impacted the natural ecology of the Earth.

The weather patterns of our Earth are regulated by a vast system of atmospheric conditions which force air and pressure up and down across the globe. The basic structure of the nature of atmospheric conditions comes from a familiar source, the sun; "The central feature of global weather is the redistribution of solar energy that falls unequally on Earth at different latitudes," (Manahan 2006:193). The sun heats up the earth's surface unevenly, causing mixed reactions between the warmer air of the tropics, which are closest to the sun at all times, and the cooler air of the icy poles. The earth moves hot and cold air around to mix them and keep temperature in check and regulate weather patterns. The three cells that dominate over atmospheric circulation have a fluid structure which does vary annually, yet generally stays similar in nature.

The largest of the three cells and most forceful in climate conditions as we know it is the Hadley Cell. Located over the equator zones, this cell moves hot air u into the atmosphere from the earth's surface, for hot air always rises higher than cooler air. The excess energy caused by the warmth in the air near the equator causes that air to rise until it hits the troposphere, where it "cools by expansion and loss of water, then sinks again," (Manahan 2006:193). This motion of hot air rising, cooling, and sinking again results in a high pressure zone. It also creates the Coriolis effect, or "The air in the Hadley cells does not move straight north and south, but is deflected by Earth's rotation and by contact with the rotating Earth […] which results in spiral-shaped air circulation patterns," (Manahan 2006:194). This circulation combined with hot air pressure can result in great weather instability in the region. Such patterns create the environment for large tropical storms and hurricanes as hot air cools and sinks with the warmer air. Yet as destructive as this force may be in terms of erratic weather patterns, it has also been the foundation of one of an extremely useful oceanic current system. According to research, "The movement of air in Hadley cells combined with other atmospheric phenomenon results in the development of massive jet streams that are in a sense, shifting rivers of air that may be several kilometers deep and several million kilometers wide," (Manahan 2006:194). These jet streams, found over both the Atlantic and Pacific Oceans, redistribute and influence weather patterns. They have created currents and trade winds which people have used as oceanic trade routes for centuries.

At the other extreme of the spectrum is the Polar Cell, located in the much cooler areas of the Earth. It is located in the most remote regions of the Earth, starting at around the 60th parallel. The Polar Cells are dominated by cold air caused by "Strong radiational cooling near the poles causes polar air to become cold and dense, which in turn causes it to sink," (Washington & Parkinson 2005:17). Cold air becomes extremely heavy and falls back towards the Earth's surface. The cell itself is extremely weak "although it remains detectable in times of averages of the air circulation," (Washington & Parkinson 2005:17). Like the Hadley Cell, the Polar Cell is driven by heating and cooling patterns. It helps balance the warmer air found in the tropical regions.

Unlike the direct Hadley and Polar Cells, the Ferrel Cell is an indirect cell which acts as a buffer between the two other cells. According to research, "The Ferrel Cell is an indirect meridional overturning circulation in mid-latitudes," (Vallis 2006:480). It is located in the mid-zones between the two extremes. The Ferrel Cells are present in both hemispheres within the middle and high latitudes. The flow moves towards the poles closer to the ground and it is and towards the equator in the middle; "cool air apparently rises in high latitudes, moves equatorwards and sinks in the subtropics," (Vallis 2006:480). Moving towards the equator it helps distribute colder air from the Polar Cells. It is also regulated by a friction which helps it keep moderate and controlled, creating a low pressure zone; it "is responsible for bringing mid-latitude eddy momentum flux convergence to the surface where it ay be balanced by friction," (Vallis 2006:481).