Atmosphere And Weather

Factors that Affect Wind Direction and Speed



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Simply put, wind is the movement of air. It is created by air moving from zones of high pressure to zones of low pressure. Air pressure refers to the weight of the Earth's atmosphere pressing down on Earth's surface. Winds blow due to several factors: the sun, the shape of the Earth, rising warm air and sinking cool air, and the rotation of the Earth. Winds can be created by the temperature differences between land and sea. Winds may also form up and down mountain slopes.

Wind Direction

Sunshine gives off energy, but it does not land evenly because of the fact that the Earth pretty much has a spherical shape. If the Earth were flat, all areas of the Earth would receive the same amount of sunlight. However, the curved nature of the Earth causes some areas to receive more sunlight than others. The equatorial areas clearly receive more sunlight than the polar regions of the planet.

Air heats up much more quickly at the equatorial regions and as it rises cool air rushes in to take its place. While this is taking place, the cold air over the poles is sinking due to the fact that cold air is denser than warm air. (This means that its molecules are packed more tightly together.) A current forms between the air rising over the equator and the air sinking at the poles.

The air over the equator rises and moves towards the poles where it cools and sinks. This air then moves back toward the equator where it heats and rises once again. This process is a continuous cycle and is referred to as convection current. Smaller sections of this current are called convention cells.

Interestingly enough, the rotation of the Earth also has an effect on the wind's path. As the Earth rotates the wind is deflected. This means that the wind's path is bent as the Earth turns underneath convection currents. This rotation skews their path creating an effect called the Coriolis Effect.

The Coriolis Effectwas named after a man named Gustave-Gaspard de Coriolis. Coriolis was a French physicist who lived from 1792 until 1843. He first identified the Coriolis Effect in 1835.  According to science writer, Desonie, the Coriolis Effect is the tendency of an object to move sideways as an effect of the Earth's rotation.

Reader’s Digest Weather describes major wind flows over the Earth as “the general circulation of the atmosphere or global wind patterns”. Both the northern and southern hemispheres of the Earth experience three major circulations of air: the Hadley cell, the Ferrell cell, and the polar cell. The Earth's rotation deflects air differently in each cell and the regular wind patterns (or directions) that occur as a result of the Coriolis Effect are called: Polar Easterlies, Westerlies, and Trade Winds.

Wind Speed

Wind speed depends on several factors as well. A major factor that determines wind speed is the difference between the areas of high pressure and low pressure. The greater the difference between the two zones, the greater the wind speed will be. In other words, when air is drawn from a large area toward a small center, stronger winds will be generated. This is what happens during hurricanes and tornadoes.

Another factor that affects wind speed is location. According to Smithsonian's Earth, the wind is always stronger over the ocean than it is over the land. The friction on land created by hills, trees, structures, and other types of obstructions has a tendency to slow wind down. There is much less friction over water than there is over land and winds can blow uninterrupted over much greater distances. High-altitude winds such as winds over mountains can also have exceptional strength and speed.

Wind, the movement of air across the planet has an awesome effect on everyday life. It is one of the major factors that determine weather and climate across the world. Wind speed and direction are determined by many things and the entire process can seem quite complex. However, one thing remains perfectly clear; wind is a most powerful force.


References:

Desonie Ph.D., Dana. (2007). Atmosphere: Air Pollution and Its Effects. New York: Chelsea House.

Luhr, James F. (2007). Smithsonian Earth. New York: DK Publishing.

Reader's Digest. Weather: New York/Montreal: The Reader's Digest Association, Inc.

Science 5: Teacher Guide. (2007). K12 


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